On October 19, 1992, at its headquarters in McLean, Virginia, the United States Central Intelligence Agency held its first in a series of intelligence history symposiums, open to the public, historians, and the press. Inspired by the view that the study of intelligence is frequently overlooked in the analysis of history, the CIA brought together on this day the major participants in one of the defining events of the Cold War. The Cuban Missile Crisis of October 1962. Thirty years earlier, on October 15, 1962, in an unmarked warehouse in Washington, a photo analyst for the CIA was examining aerial photographs of the rugged terrain of Cuba. To the untrained eye, these photographs seemed innocuous, but CIA photo interpreter Vincent di Renzo saw something very menacing in the oblong shapes hidden in the woods just northwest of the Cuban village San Diego de los Paños. By measuring the size and shape and comparing them to manuals of Soviet missiles, smuggled out of Russia by spy Colonel Oleg Pankovsky, he could confirm that what he saw was equipment associated with the SS-4 ballistic missiles. With a range of 1,100 nautical miles and a payload of nuclear warheads, they represented a major threat to the balance of power between the United States and the Soviet Union. For these missiles could reach as far north as Washington DC and as far west as Dallas, Texas. At 11.45 the next morning, intelligence officers Arthur Lundahl and Ray Klein told President Kennedy that the Soviet Union was erecting offensive missiles on the island of Cuba. The President's manner was business-like as he turned to Lundahl and asked, Are you sure? Lundahl replied, Mr. President, I am sure of this as a photo interpreter can be sure of anything. In the next 13 days the President would be brief daily on the status of the missiles, with new surveillance of Cuba showing what progress the Russians had made overnight and how many hours before the missiles were operational. Armed with this information, Kennedy could buy valuable time to plan a strategy on how to confront the Soviets. Today historians continue to look at the Cuban Missile Crisis and its key players to discover the lessons of diplomacy in the modern era. But until the CIA's symposium, much of the first-hand experience surrounding the crisis was based on speculation. What follows are edited excerpts from this symposium. The panelists first discussed the intelligence activity which led to the discovery of the missiles. As Deputy Director of Plans at this period I was charged with espionage, counterespionage and covert action. That year, 1962, saw Cuba in the forefront of our activity. Having lived through the trauma of the Bay of Pigs, we recognized that its failure hung over the Kennedy Administration and dominated the work of all of us in the Plans directorate. Let me emphasize, President Kennedy wanted to get rid of Castro and his communist government, period. Operation Mungoos had been in effect for a year before the crisis. Secret agents were being recruited and trained for work in Cuba. The Opa Laca Interrogation Center was processing refugees from Cuba as rapidly as sound interrogation procedures permitted. Tales of Soviet weapons being seen on the island filled the press, the radio, intelligence channels. Senator Kenneth Keating of New York was making life miserable for the intelligence community by asserting repeatedly on the Senate floor that offensive missiles were arriving in Cuba at a time when every analyst was bursting his britches in an effort to verify the truth of these allegations. To say that the agency's operational arm was stretched taut and thin is to understate woefully. Given these circumstances, all of us were hard pressed to verify the multitude of reports we were getting about sightings of missiles and other types of Soviet offensive weapons and equipment. It was a mammoth undertaking. But where possible, we checked every weapon report against U-2 photography of Cuba and against other intelligence sources. Samuel Halperin, Task Force W official, and Warren Frank were involved in the gathering of intelligence in Cuba. We all felt we'd said so over and over again we have to get some intelligence first. We have to know what's going on in the island, who's doing what to whom, because after the Bay of Pigs we were left without any assets at all in the island. We then started to create an organization with a station down in Miami or south of Miami called JM Wave, which at one time was the largest station the CIA had in the world until the Vietnam activities in 65 and there on. The station in Miami was set up as originally I guess as sort of a cleanup to the Bay of Pigs activity. We had a lot of disadvantages for the one thing we had no agents in Cuba. There was no embassy there, which is usually the place you start to do some research or something. So it was kind of a tough assignment. We had some advantages though. There were a lot of Cubans in Miami and these were the first wave of emigres, as is common in most places where a communist system took over, were the professional managerial business class. These people got out early and had remained in contact with their families and friends and associates in Havana, so there were a lot of contacts existing. In September and October of 1962, field sources reported missile-like objects moving through Cuba. We had at least 75 to 100 reports of long missiles, not the sand but the palm tree sized missiles. These were observation reports and we had good observation reports from the unloadings at Mariela, which were not disseminated by Washington. And there's no photographic proof of this of course because it was done in the middle of the night and the U-2s didn't fly at night. So these things were ignored. We had many reports on these SS-4s which turned out to be being stuck on corners. They couldn't negotiate the corners because it was called traffic jams. They had to back up and everybody in Cuba is a little country. People find out about these things, so there wasn't that great a secret. The problem of noise or having too many reports of different quality kept the legitimate reports from reaching policymakers. Our view in Miami I think was consistently that Washington had locked itself into a position with the national intelligence estimates that the Soviets wouldn't do this, wouldn't put missiles in Cuba. And this we felt tended to prejudice them against our reports in which we had a great number, we can discuss this a little later, of missiles in Cuba. The first reports we got of large missiles in Cuba were of missiles the sizes of palm trees. Well we got a whipper snapper in from Washington one day saying a palm tree, this is meaningless, a palm tree can be a six inch seedling or a 120 foot royal palm. Therefore all these reports are rejected. When the Cuban talks about a palm tree the national tree in Cuba is a royal palm which is 60 to 80 feet. Ray Hofstetler then analyst at CIA headquarters spoke about the problem of verifying the many and often conflicting sources. Prior to January 1962 we had already received some 200 reports of missiles in Cuba. Of course this was before there were any missiles at all. The problem of separating the wheat from the chaff was a problem of trying to correlate events of cross-check checking the references and of trying to pull up out of an enormous amount of confusing misleading sometimes contradictory reporting what the patterns are upon which you might base a judgment as to the facts extend at the time. On the one hand you had refugee reporting coming in a lot of it helpful. Indeed a lot of it helped us to pin down areas which later were to be photographed and targeted for technical coverage. You had agent reports on the island coming in and you had technical collection both in aircraft flown imagery and in signals intelligence which we have not talked about this morning and actually which we're not going to talk much about at all. But nonetheless there are a variety of different sources coming in. All of these had to be cross-checked to try to determine pin down what the facts were. Another situation which I think you heard well depicted today both in Vince's discussion and in Warren's discussion is the problem of being able to determine what a single report means. In this case let me say that a picture is not worth a thousand words. A picture brings to anybody a new piece of information against a background of understanding. And I think the impression that I had that I would like to share with you is that trying to figure out what the facts are when you have reporting from so many sources is indeed a daunting task. It was popular opinion that the Soviets would not put offensive missiles in Cuba. John MacCone the new director of the CIA felt differently and demanded close U-2 surveillance of the island. Now MacCone had been sensitized to Cuba ever since he took office and he also ended up with a very firm personal conviction about the possibility of the introduction of Soviet missiles into Cuba. His reasoning I think is worth a brief review. He says Khrushchev knows the state of the strategic balance and he knows that we know. Now how can he possibly redress it? Well he has an absolute plethora of IRBMs and MRBMs he's got more missiles than he has targets. He has never deployed one outside the borders of the Soviet Union but in Cuba he has a piece of real estate where he can do that without fear that falling into unfriendly hands those missiles could be redirected toward Moscow. If he said I were Khrushchev I would put offensive missiles in Cuba. I would then bang my shoe on the table and I would say let's talk about your overseas bases. Let's talk about Berlin and let's talk about any other subject that I choose. Dr. Albert Whelan shared MacCone's suspicions. Because I was new to CI because I'd never read clandestine reports I used to stick around here every night until about 9 o'clock reading a big stack of them myself rather than asking the staff to read them for me. I recognized full well that the Cubans were trying to stimulate us to take action to liberate their country and that there was a great deal of falsification and fabrication going on. I was struck however by several reports several clandestine reports that are not unfortunately in your package. It described a convoy this was prior to this was in early September a convoy of very long devices moving through Cuban towns and having to turn corners on these small village roads which are characteristic of the Caribbean area that I knew something about and having in order to negotiate these turns to remove mailboxes and light poles and I said to myself a fabricator would not have thought of that and I was convinced at that moment that there really were very large objects probably missiles certainly not SAMs that were going into Cuba. It seemed to me that with this data unless one could refute it there was no reason not to jump to the conclusion that they had probably taken a very big gamble after all they put a big defensive ring in place. It did seem to me that it was a pretty sensible move if they could take the missiles that they had already built and had deployed in Eastern Europe transport them across the ocean, install them and then suddenly they would be added to the strategic balance. We were about even at that time about but by doing this they could effectively increase and would have had they continued their strategic inventory of nuclear tip rockets by about 50% virtually overnight and so it was a bold move but one with a big payoff it seemed to me. I knew that a special national estimate was being prepared and I went to Sherman Kent virtually on the eve of that estimate. I presented the best case I could to Sherman he was courteous to me I think Sherman liked me. He knew that I knew something about missiles but after listening courteously he said well the die is cast and we're going in a different direction and I felt at least that I had my moment. In the five weeks prior to the crisis reconnaissance flights over the most sensitive areas of Cuba were grounded due to the loss of a U-2 over China and a fear of State Department officials of an international incident. John McCone who was on his honeymoon in France at the time was unaware of this until he returned. He immediately convinced an interdepartmental group to allow one more U-2 flight and on October 14th at 731 a.m. Major Richard S. Hazer boarded a U-2 reconnaissance plane and flew Mission G3101. He returned with eight cans of film containing 464 frames of imagery. The film was processed and sent to the headquarters of the National Photographic Interpretation Center. Former Chief NPIC Information Branch Dino Brugioni and Analyst Vincent DiRenzo discussed the process of identifying the missiles. About 2 p.m. I received two cans of imagery with the target sheet titled Possible Missile Associated Installation. I looked at the target area on the imagery and noted groupings of equipment scattered along the tree lines. I had the team begin a systematic analysis of the imagery. We needed location, precise geographic coordinates, equipment ID and counts. The scattered collection of vehicles and tents was similar to and yet different than very early deployment of SAM sites and SAM support equipment. Size and shape of the long canvas cover trailer was very unusual. The shape was different and the length being 65 to 70 feet long and 9 feet wide. Especially the length was almost twice as long as any trailer associated with any Soviet defensive system. There were no breaks in the canvas support frames to indicate two or more vehicles parked together or that two or more trailers might be parked end to end. This was a single unit and it was designed to carry one long object. The pattern started to develop in my mind. The signatures didn't fit anything in any of the systems that we were expecting and what we saw being deployed in Cuba at the time. There were no parent ties to any normal military field units nor electronics and nothing fit dummy or decoy activity. There was just too much activity. Yet the equipment appeared to be missile related. With that I started to weigh the possibilities of an offensive system. We assembled all the information we had on the system and at that point being convinced that we had the SS-4 missile plus the associated equipment, I called Dino and asked for some additional support to make sure that we considered all possibilities. We looked at his specialized files of SS-3, SS-4, SS-5. We checked the various photos, prints, details that he had. After seeing again the parade photos together with the photogrammetric measurements Dino had, I was convinced without a doubt we had the SS-4 system. I turned to the team members and said this is an operational field deployed MRBM site. They checked the site, made measurements and fully agreed we had our first MRBM site. Richard Helms then described the details of briefing President Kennedy. On October 16, President Kennedy was informed that Soviet offensive missiles had been found in Cuba. It was a bombshell. He was shown photographs of SS-4 medium range missile launching installations under construction at San Cristobel in western Cuba. To the untrained naked eye the photographs looked like a football field being excavated. From the missile manual that Pankovsky had transmitted in 1961, the intelligence community knew all the operational details of the liquid-fueled SS-4 missiles. What the photo reconnaissance team saw in the U-2 aerial photographs was a characteristic deployment pattern or a footprint of the SS-4s that was shown in the missile manual supplied by Pankovsky. Pankovsky's manual assisted the intelligence community to estimate for President Kennedy how long it would take to complete the installation. We looked at power and fuel lines, launching moons and all the other details which were in the manual. The assessment gave President Kennedy several extra days. The big issue of the moment was whether to send in our air force to take out the missile bases and the army to invade the island. With the aid of the material Pankovsky delivered, we were able to tell the President, quote, this is what we've got here and it will take them X days to be ready to fire, unquote. It gave President Kennedy time to maneuver. I don't know of any single instance where intelligence was more immediately valuable than at this time. After what Ray asked Robert Kennedy and McGeorge Bundy how much they thought that single piece of evidence was worth. Both men agreed, quote, it had fully justified all that the CIA had cost the country in its preceding years, unquote. Missile expert Sidney Graybeal and Albert Whelan described the daily briefing of President Kennedy. And essentially what they were looking for was a question of are these missiles ready to be fired? The answer was no. The question was how long would it take? As was pointed out earlier, Pankovsky had provided us invaluable information on how these missiles operated in the Soviet Union. This is the first time they'd ever been shipped out of the Soviet Union. How were they packed? Cosmoline, what was the difficulties that unpack them? We knew they had to be erected. We knew that the war had to be mated. We knew they had to be fueled. We knew roughly the time factor it would take operating inside the Soviet Union. And we explained this to the President. There are many unknown factors in this. But when the question came up, how long would it take? It would take two hours roughly to make the warhead. But to make the warhead then you have to erect and do the fueling. So you were talking hours, even when the missile was in good condition and had been brought out. We were unable to confirm the nuclear warheads there. But it was our opinion, contrary to what McNamara wrote in the New York Times piece recently, that the CIA advised them that the nuclear warheads were not there. What we advised was we had no evidence that the nuclear warheads were there. But I think most of us felt that they wouldn't put these missiles there in the position they were in without the nuclear warheads. And as Dino pointed out, we could see all the necessary equipment, even though you didn't have the nuclear storage facilities and the security. The key thrust of all of these questions though, an important point here, the President really wanted to know how much time did he have to act? For me, the most challenging questions that Kennedy put to me were, and he pointed his finger right at me a number of times, he wanted to know how long he had to make his decision. And that really turned on how long it would take to bring the missiles to operational configuration. And in this, we were fortunate in having the Pankowski material. I'd known enough about this operation to know, to believe them. And the manuals were absolutely important, absolutely essential, because they really told a field commander how to set these things up and what the timelines were. And so with great confidence, I could answer the President's question and give him a hard answer, which I think he deserved. The panelists then discussed the process of estimations and why on September 19, 1962, roughly a month before the crisis, the CIA's Board of Estimates issued a statement concluding that the Soviets would not install offensive missiles in Cuba. I remember spending all of one Saturday morning with Sherman Kent after the estimate prepared going through every one of these reports and trying to figure out which ones were. And still we had these four or five reports that appeared legitimate, but in our view was not enough to change the basic thrust of the estimate. We had somewhere in the order of two to three thousand reports. And Sammy mentioned before some of these reports that were very accurate, that they collected in Cuba, but were never disseminated. You've got to remember that at that time the analyst looks for hard facts. Every one of these reports that reported missile activities, we would take to NPIC, and NPIC would look for the photographic information and all of them that they could confirm with photographs were negated. However, remember, and the material passed out to you shows that the U-2 was not permitted to fly in the entry of the Cuba during this extended period of roughly three weeks. At the time, I didn't know all of this as an analyst, I was told that weather was keeping the U-2 down and we weren't able to fly due to weather conditions when we were pressing for more of the Cuban flights. Roger Hillsman During the summer of 1961, when the satellites showed that the so-called missile gap was in our favor and proved it, we had a knock-down, drag-out discussion in this town, which Dick, you will remember well, trying to decide whether we're going to tell the Soviets that we knew the truth. Now, the intelligence community didn't want to tell me. You don't want to reveal any of your sources. But they were turning the screws on Berlin, and the decision finally was to tell them in as low-key a way as possible. I think we handled it well. Now, my point is this. Everybody in town and in the intelligence community knew that this would scare the Soviets very much. And that they would do something desperate. We knew they had plenty of MRVMs. We knew they were running out of their ears. We knew they had plenty of IRVMs. We thought there would be a crash ICBM program, but none of us, me included, thought that they might move those MRVMs. We didn't even raise the question and discuss it, or at least I never heard discussed at UCIP or elsewhere. Now, that, I think, was a real estimating failure. And the reason I say so is that by the time that the president and the White House and the policymakers were alerted to the possibility, the decision had been made. The ships were on their way. Kennedy began to talk to Gromyko. He made his speeches in September. I can't believe, I can't believe that Kushov or any major chief of state is going to reverse that major decision that's already been made and being implemented on the basis of a few talks with Gromyko or a couple of public speeches. But if Kennedy had made those speeches in January or March or February before the decision was made, the missiles may not have showed up in Cuba at all. Hillsman argued that estimators have a different role than policymakers. As an example, he used Winston Churchill in World War II, predicting that the Germans would attack Russia. Well, Churchill makes much that the British national intelligence estimate of the time did not predict, I mean, the German attack on the Soviet Union until just about two weeks before it occurred. But he says, I, Winston Churchill, immediately cabled, and this is in February, immediately cabled Stalin to expect the German attack. Well, now that's a policymaker's right to take one agent report and put a lot to it because he is making a policy act. He's saying something to another head of state. If he proves wrong, he pays the policy cost. But if an intelligence estimator says that one agent report indicates to me the Germans are going to attack the Soviet Union, he is preempting the head of state. And that's one of the reasons it doesn't happen. Now, what difference did it make? First of all, I once, I confronted Joe Newbert, who was one of our senior Sovietologists in the State Department, along with Hal Sollenfeld, about why were you wrong about the September 19th estimate? Why were we wrong?  You can only estimate that he's going to behave sensibly and logically.  He said, you can't ask an estimator to do that. So my point is, don't feel too bad about the September 19th estimate. It was a correct estimate. The Soviets made a mistake. You can't estimate that they're going to make mistakes. The floor was then open for discussion. Chester Cooper, I agree that the Soviets made a mistake in putting the missiles in Cuba. I would submit that we made a mistake in saying that they wouldn't put the missiles in Cuba. My sense is that we got paid, not for trying to predict what was logical, but rather to predict what was likely to happen. Anybody can predict what was logical. And the Office of National Estimates was supposed to obviously consider what was logical, but also consider what might happen in any case. Okay, but Chad, if the September 19th estimate had said, we think the Soviets will put missiles in Cuba. Now, I didn't assign that estimate, so I'm able to defend it a little bit better than some of the rest of you guys. But if we had had an estimate that said, the Soviets are going to put missiles in Cuba, what would the United States have done differently than what it did? Let me say something. Intelligence and policy are different fields. Intelligence in the Central Intelligence Agency has to make estimates. They have to make probabilities. They're very problematical. Now, policy is different. John MacCone talked about policy. He talked to the president. He sent messages to the president. And he understood that he didn't know exactly what would happen, that policy is a different relationship with the president than the CIA and the intelligence community. We have a question on the right here. Charles Davis, if we do not take the risk of being wrong or of saying the other person would make a mistake, that means that we'll never make a correct estimate. We wouldn't have made a correct estimate when the Germans invaded Poland. When this particular crisis occurred when the Arabs attacked Israel for 17 times. We will never make a correct estimate unless we take the risk. Charlie, I'm going to take that as a statement. Not a question. I'm going to recognize the person in the back on the right. Had the September estimate been different, do you think that Dean Ross's arguments that you two flights shouldn't have continued over Cuba would have held sway in the government? Seems to me that one of the great revelations today is that there was a whole month there when a number of people were making the right call but yet intelligence assets were not used to discover the information required to achieve closure. So maybe that estimate did have an effect on requirements. Maybe I will answer that one because I have read the summaries of the Executive Committee meetings that have been released by the Kennedy Library and Ross's point of departure was the loss of a U-2 over China which had occurred just in advance of the meeting where scheduling of the U-2s was to occur and that was primary in his mind. He was concerned about another international incident. Of course, he had no idea that there were missiles in Cuba and it seemed imprudent to simply delay for a while. The delay was put in place and was not broken until as Walt Elder tells us, McCone came back from his honeymoon, discovered it. I think you expressed it rather moderately. My understanding from eyewitnesses is that it was an explosion on the seventh floor of the CIA and he then persuaded the XCOM to re-institute the flight. So in a way it was an accident. Two historians were asked to give commentary. George Herring from the University of Kentucky. But I do see running through intelligence crises or intelligence failures, whatever you want to call them, problems of intelligence from Pearl Harbor through the missile crisis, through the Tet Offensive in 1968, through Kuwait even, one sort of thread that we have alluded to a couple of times and talked about and I think perhaps would do well to come back to over and over again and that is the inability to conceive of an adversary or a potential adversary to do something as apparently rash as a surprise attack on Pearl Harbor or placing missiles in Cuba or the like. Maybe as Roger Hillsman suggests, we can't estimate that the other person is going to make a mistake and one could argue that in each of these cases, ultimately it does turn out to be a mistake but still I think this is an issue that we need to raise and need to grapple with. I as historian don't. I can sit back as the Monday morning quarterback and simply say why and stop there but I think it is an issue. It comes up so often. It seems to be the fundamental flaw that it must be considered. Graham Allison, former dean of the Kennedy School of Government at Harvard University, an author of The Essence of Decision. I think while this is ancient history, it still remains the best window we have, cloudy as it is, into the real risks of nuclear war and the kind of calculations that leaders make in these circumstances. I think the missile crisis also serves in a nutshell as a good symbolic reminder of the major strengths and the major weaknesses of American intelligence, particularly in this domain of analysis and estimates. Let me begin with the bottom line so we're not confused. This was a success. Net a substantial success. Intelligence succeeded in identifying for the president and the policy-making community before weapons were operational that could threaten the U.S. the presence of these weapons. Indeed, looked at in historical terms an extraordinary success. That's the bottom line. But let me talk then first about strengths and then secondly about weaknesses. In strengths, this exhibits clearly the major strength of American intelligence if we try to put it in a big historical picture, which is technological magic. The capturing of pictures from overhead reconnaissance of activity on the ground in 1962 was an act of stunning technological virtuosity, not approached by any other country in the world, never achieved previously in history. Today it's almost impossible for us who become familiar with it to understand what it meant or the frontier that had been pressed by this. If you ask yourself, what if? This is a way to bring this home. What if this technological capability had not existed? If not, the judgment recorded in the September 19 estimate that the Soviet Union would not install offensive missiles in Cuba, would have stood, the missiles would have become operational, Kennedy would have faced a fait accompli, and the outcome would have been quite different. So that's the first strength. The second strength is what Dick Helms pointed to today, namely quality human intelligence. And I'll only say on that that I agree entirely with what he said. Let me turn quickly to the weaknesses. Weaknesses in analysis and estimate. And I'll underline three in the notorious September 19 special national intelligence estimate about which the other members of the panel have spoken. First, the point for us here is in the first failing that organizational indicators that provided indelible clues for intelligence, especially organizational SOPs, were difficult to interpret but weren't captured and interpreted in this instance. Second failure. The failure to acquire and interpret the significance of these indicators reflect a second weakness, which is a weakness of mirror imaging as against really getting within the skin or seeing the world through the eyes of the opponent. Third failing. Alternative futures. This notorious special national estimate of September 19, which is included in the materials, concludes that the Soviet Union will not make Cuba a strategic offensive base, will not put strategic offensive missiles in Cuba. Now, as we've heard in both panels this morning, John McCown, the director, had a different idea. Bud Whelan had a different idea. But the intelligence estimate is very categorical. If the intelligence estimate had been prepared to consider alternative futures or maybe even put in an addendum that said, let us discuss a possible alternative, asking what the consequences of such an alternative would be and trying to identify what the indicators that such an alternative might be emerging would be to which the intelligence collectors should have been especially alert, one might have gotten a different outcome. And there, I would like to applaud a new policy of the agency or at least one of its directors, I understand it, who recently in a speech said the following, when assessing events or developments where the outcome is truly unknown, we must do better in exposing the policymaker to uncertainty, to alternative possibilities, and to different points of view, even while providing our best estimate. David Grease then summarized the lessons of the symposium. I won't keep you long. There are just a few points I'd like to make at the beginning. I mentioned that we were here to learn. Let me just mention a few negative points I think we've heard in a few positive ones. First, the problem of noise in the world of intelligence. So many reports. Which are the true ones? That problem has not left us. Second, mindset, the analysts who worked on those estimates who used American style logic to estimate what the Cubans will do. That problem is still with us. Compartmentation, one part of the agency knowing something that the other part doesn't know. Always a danger. And finally, forgetting the impact of U.S. policy on the adversary, something that our policymakers and our intelligence people still do. On the positive side, teamwork. Once we got going, the teamwork was fantastic. Another point, self-examination. The very fact that we're willing to argue in front of you, in public, with the press here about our own shortcomings and mistakes and try to learn from them. And finally, the synergism, which I think is the hallmark of American intelligence between old methods of intelligence like espionage and new methods of intelligence like technical collection from U2s and satellites and so forth. This is what is different about American intelligence. The analysis that comes out at the end puts the two together and makes our product a little different than that of others.


YouTube team keep it clean. What's going on? It's engraving here with another video and in this video Shout out to my guy manual you banks because he linked me the the tweet on Twitter The Ravens they signed a star wide receiver to the team and a former NF a former Texans receiver They signed a star to the team to help with this wide receiving corpse that has just been an absolute mess But before we get into who that is and this video is not going to be long because I'm almost at work already But let me introduce myself me. I'm engraving vids and this is my YouTube channel engraving vids and good morning to everybody I didn't know so much so many y'all gonna come through so fast and especially this early in the morning But anyway, like I said, this is it my name is engraving vids and this is my YouTube channel engraving vids And I'm a Ravens fan, but even though I'm a Ravens fan on this YouTube channel We talk Ravens all the time, but we just talk football period So if you're Ravens fan, it's the perfect place for you. Make sure you subscribe Or if you just love football period make sure you subscribe turn notifications on and leave a like on the video Click the thumbs up button See we got 20 people up in here, but we only got 10 likes is I guess only half of y'all like the Like the receipt or not only happy. I like the video or something man. Make sure you click that thumbs up button but anyway You also follow on Twitter Instagram and snapchat all three are engraving vids now the wide receiver that we signed is A CFL star Canadian football league star. He played under Mark Trespin's Argonauts or Argos, whatever And he was actually in the NFL before it's Debbie F. Posey Now when he was in the NFL before he played for the Houston Texans He played for the Houston Texans and a lot of you guys may not remember that name. I remember his name I remember him But the reason that a lot of you guys may not really remember him is because he didn't really do much He never broke out. He was never he never became a quote-on-quote star He never really did anything in the national football league. So this signing I Don't know what to make of this signing a lot of the things that the Ravens have been doing recently I'm not really taking much from it because they're they're starting to try out people and Assign people to spots where they need to sign people because back of QB is something that we need Receiving something that we need but they're not I feel like these are just camp guys right now These are just camp guys right now, and they're getting ready. I don't even think that this guy makes the active roster Once it comes down to the final 53, but hey, we'll see we'll see what we get there We can't say anything now, but I don't I wouldn't make too much of this signing I wouldn't look too deep into it. I wouldn't try to be like, oh man Is this gonna be for show a pair of replacement or is this gonna be the guy replacing Mike Wallace? I Wouldn't wouldn't look deep into that at all because the Superbowl was literally just two days ago the off-season free agency starts in about a month a little over a month and It's still a lot a lot lots to go down in between now and then and and the regular season So don't think too much of this signing don't make too much of this signing Don't think too deep in it. Don't be like, oh man, is this gonna be the guy that takes us over the top Because it's not it's not just to be honest. It's not Um, it's just a sign and probably like I said, probably a camp body for once. Um, that time comes around I mean, obviously you hope for more for the guy. Um, you hope for more for the team But like I said, don't don't think too deeply into this thing because Uh, it's it's most likely not gonna really be anything. Anyway, appreciate y'all. Thank you Thank you so much for y'all coming through this morning. It was 30 people up in here Early the early morning. I didn't I didn't expect that I expected maybe like five Maybe 10 people to show up this morning, but I appreciate y'all man. Thank you. So I'm about to head into work now Appreciate y'all. Thank you. Make sure you subscribe to the channel if you haven't already leave a like on a video If you haven't already and turn the notifications on so when we go live Even randomly like this in the morning. I missed doing these morning streams But anyway, let me get to work now


Today, I was sent a secret mystery box from a viewer. What's up, guys? We're back with another epic video. And in today's video, I have a massive box here that was sent to me by a viewer. I opened it up real quick, but he has a read first thing. So we're gonna keep that in there before we actually get to it. You might be wondering, what's a secret mystery box? I mean, aren't all mystery boxes a secret? Yes, technically they are. But the secret part about this is they're not actually a secret. So one of my viewers actually told me, hey, you need to check out walmart.com because they've been selling these mystery boxes and they're supposed to have a chance at all the legacy packs. If you guys remember those, it's like you could have an entire box of just like old school reprints. He found out apparently on the Walmart one, every time he buys from there, they're all the reprints. So it's like the one in five seated chase, he's getting it every single time. So I naturally went on Walmart myself and went to buy some. Apparently they were out of stock. So I was like, well, I guess I can't get any. And he said, hey, how about I just send you a couple? So we don't actually know if these are like all mystery like reprint packs or whatever. But according to him, every single time he bought from there, it was. So we're about to find out today if we have the secret hack to getting all legacy packs. Hey, Phil, excited to see what you pull out of these boxes. I opened five and they all had at least five legacy packs. So he's five for five. I'm like, it's like 20% chance usually, but apparently not. Also with an interesting history and after a long journey, this item's being passed on to you so that you can give it away to the community. That's an interesting story, which you are free to share. Challenge to the comments section, spot the error with this item and take your guests down in the comments. Feel free to follow him on what not that you were training and on Instagram. So go check him out. Let's see what he sent us for the giveaway. We have a CGC slab. Okay, that means, I mean, he said error, didn't he? So CGC is known for their errors. We have done a CGC return recently. Go check it out if you guys missed that one. That's pretty awesome. All right. We have a CGC graded card. Let's see what it is. All right. It's the forbidden chalice signed by Ruxen 34. So yes, this is a card I've personally experienced. I think this was actually in the vlog where I signed this card. So if you guys remember the Charlotte vlog, I met up with Uber trading and he had this card. He asked me to sign it. I was like, are you sure you want to do that? And he's like, oh yeah, let's go for it. So I think it was like a PSA for something. It actually got worse because of this. Apparently no qualifier for Ruxen 34 signature. Not that famous, I guess. We don't get to be on the label. That would actually be pretty sick. But a signed by me, this is on the card, not on the slab. So I signed this while it was raw and then he got it graded. We'll re grade it because it was a PSA. So this is really cool. You guys can win this now. The Ruxen 34 signature. Ultimate rare, by the way, for Ben Chow. So that is super cool. I'm really excited for that to be the giveaway. Just like the video, be subscribed, turn on notifications. Let me know what you think about this secret mystery box. Do you think that they only sent out a certain amount so that it would be the one in five seated rate and they just kept all of those like in a different area or something? And now out of that specific warehouse they're using, they're just sending out the good ones? I don't know. I'm not sure why that happened. All right, so here are the mystery boxes in question. They can potentially have six legacy packs. I don't even think these were the ones I was thinking of. I wonder why these have so many legacy packs. There was one where it was like, it said like you had a chance to get all five. I don't even think this is it. So this is interesting that it's just all legacy packs. Let's just see if these are the same. I'm excited about this. He also sent us some chaos boxes. I'm gonna save them for a different video because you know, this is a ton of content with these three. Let's get into it and I'm excited about this. Notice how excited I am because I said it two times. All right, here we go. Moment of truth. Let's open this thing up. We have opened a bunch of these, if you guys remember, we never had like crazy mystery luck on it. Like we didn't get like five legacy packs ever when we did it. And I got a lot of these from my like local Walmart. So maybe that's why I didn't really buy from Walmart.com. So Walmart.com might be the hack. I don't know, we're about to find out. We're gonna open it up like this. Let's start off with the deck. We can do that. We've got a mechanized madness, which you know, we get this one quite a bit out of here. This is a pretty common structure deck to get. Actually a pretty cool deck. I've made a deck myself out of it and played with it a lot. Pretty fun. Okay, next one, let's go. We have a Legend of Blue Eyes pack. Oh my goodness. It's actually starting. So we either pulled out the one legacy pack or they're all in here. So let's start off with Legend of Blue Eyes. Let's see what we can do. I think this is the pack trick. We have Ayame with the Missouri zombie. We've got the witty phantom, Wasteland, the R-Mail, Two-Mouth Dark Ruler, Fire Yaru, King of Dark Abyss. Just kidding, that is not the right way to say that. Giant Soldier of Stone and the Beast Fangs. All right, so we're starting it off with nothing on that one. And I also wanna remind you guys while we're doing this, first let's do another reveal. Let's see what we can get out of here. Second pack, this feels like a legacy pack. It is, it's an invasion of chaos. He found the hack. He found the secret way to get all the packs. This is insane, okay. All right, this is cool. Let me know in the comments if you have ever done this before and you've ever had luck like getting all of these like super hack packs. You know, this is nuts. We have a Molten Zombie. We have a DNA transplant. Oh yeah, I was gonna remind you guys do not respond to any scammers in the chat in the YouTube comments. I mean, don't send them any money for shipping or anything like that. Giveaways are announced in the YouTube community tab. We're all the way caught up, by the way, which is awesome. Grand Maju Day eyes at heart of the underdog. Be gone, naive. And berserkerilla, okay. And will it be a chaos monster? The thing in the crater. So I mean, it's a thing in the crater. That's not a chaos monster, okay. All right, is it possible that there's another one in here? Come in, come on, no way, right? No way. Invasion of chaos. This is nuts, dude. This is so weird because I've opened so many of these. Remember these are the ones we got Stardust Overdrive and Docs and stuff like that? We would always get the same packs. Like we get the same few packs every time. We would never get like, you know, we get one legacy back. That was it, okay. A drama block, very nice. So far we haven't pulled anything. Tower of Val, we got the fin rear. Sacred Kran, we've got the multiplication of ants. A hero emerges, very nice. Be gone, naive, with the giant hand right there. Very nice, okay. We've got the mad dog of darkness and from darkness, secret rare. It's the wrong one though, unfortunately. But still, secret rare, very cool, we can guard. This got a reprint in tactical masters. Nobody really knows why. I mean, it's just randomly in there. All right, fourth pack. I've readjusted, my back was killing me. Let's see, it feels like, oh my gosh, three IOC packs. These mystery boxes are insane. Oh my goodness. I know you guys are gonna be checking Walmart after this. But when I checked, there was none. So I don't know, maybe they're re-stocked. I don't know, I'm gonna double check myself because I would like to get a couple of these. Spatial collapse, we got a seal feed. Crimson ninja, chaos end, heart of the underdog, Joey Wheeler. We got the Grand Maju Day Isa, somehow still relevant. Primal seed, the Getsu Fuma. Come on, here's where we want the other secret rare. Can we get two secret rares out of three packs? Let's go. Agale, Lizard. All right, actually not that bad. You know, you get to return a monster to your opponent's hand. Not that bad for old school. Okay, we got two more packs in here. There's a blister, and then there is a legend of blue eyes pack. Two LLB, three IOC. That's insane value right there. Okay, Uber trading. Once again, shout out to him for hooking me up with these for a video. Really, really cool. He was actually a really, really nice guy when I met him in person too. So really, really nice. Trip, wire beast. We got the basic insect, the Furious Sea King. Petite Angel, the Green Phantom King. Awesome, lesser dragon. Mountain, very nice. Okay, and this is like a magic gathering. We got Final Flame, very cool. And here we go. A spiked, or spiked Cedra. I always call it spiked, but it's not spiked. It's just spiked Cedra. He spikes, that's it. No spike, duh. It's he's doing it now, not in the past. Okay, I gotta stop. Okay, one more. Is this probably a mystery pack, isn't it? It's a mystery pack. So is this gonna be a legacy pack too? All right, we're about to find out. I mean, we can't really complain at this point. Oh, and this is not a legacy pack. This is a, oh, Battles of Legend, Lights Revenge, that's not bad either. It's in a Radiant Mirror Force, pretty cool. What can we get? Evil Swarm, Exiton Knight, number 62. Which is a Black Force, very cool print of that. Wolf, Lightsworn Beast, that might actually be worth a couple bucks. And then Gladiator Beast, Tamer Editor. He's an editor. Do you think he can edit for the Poker Rux channel? Don't worry, we already have an editor. We found another one. Speaking of that, go check out the Poker Rux channel. If you guys are interested in my Pokemon Challenge videos, we've been doing stuff on Twitch. It's been really fun. I haven't been as consistent recently, but we've been doing at least one to two streams a week. It's been pretty fun. Next box, this is gonna be somewhat of a long video. I'd say like probably in the 20 minute range. So I know a lot of you guys really like it when I go for 20 minutes or whatever, which I personally, as a YouTube viewer, really like 20-ish minute videos as well. But I know some people, it's just too long. You want it to be 15, 10 minutes, all that stuff. But you just gotta do what you gotta do. When Uber Trading sends you three loaded mystery boxes, you just gotta open them up. You know what I'm saying? Limited holiday edition. It's almost the holidays, guys. So keep that in mind. It's almost holiday time. Let's see if this one's loaded as well. First pack, we are starting with an IOC pack. So this is a good sign for being loaded. Okay, let's go. Can we pull something good? So far we've pulled a secret rare. It was the wrong secret rare, not the one we want, but it's still a secret rare we can't complain. Thunder Crash, let's see if we can get something really cool. Molten Zombie, we've got the Hyper Hammerhead. Neo Bug, very cool. Ojama Yellow, Burning Algae, Inferno, very cool. Fumashuriken, and here we go. The thing in the crater. The crater still has a thing in it. Man, guys, don't you hate when there's a thing in the crater? It's just really killer, man. We gotta get that thing out of our crater. You know what I mean? Let's just keep going. Vicious chaos. Let's go, let's see. One, two, three, four. What can we pull here? Will it be epic? Oh, Monju, that's pretty epic, okay? It had 50 reprints recently, but still nice. Ojama Black, the Tower of the Ba-ba-ba-ba-bell. We've got the Fenrir, the DD Boarded Line. We've got the Gale Lizard, very cool. Smashing ground, Curse of Darkness, and here we go. We won a foil here. Can it be the Democ, the Black Luster Soldier? Remember how long it took us to pull that? That was insane, it's pulled again. And of course, CDs, what we want mainly. The Bogainian, that's almost more insulting than the thing in the crater. It's an eyeball with a spear. No, it's a crossbow. I always thought that was a spear. It's a crossbow, okay. Interesting, very interesting. At least he doesn't have an issue trying to figure out which eyes is dominant eye, I guess. So, he's fine there. Legend of Blue Eyes, next pack. I've never made a bad joke before. I'm just reminding you guys, they're always funny. Let's keep going. Remove Trap. We've got Dissolve Rock, Dark Energy, La Fiend Reflection Numero Dose, Las Cater Armor. We've got the Turtle Tigre, the Drooling Lizard, Metal Dragoon, all right, here we go. What will it be? It's a King Fog! Oh, come on, man, where are the L.O.B. foils? Come on! This is not perfect ratio like that video the other day when we opened L.O.B., go check that one out if you missed it. Still a lot of packs. Oh, we forgot to get our deck first. Oh, a Mechanized Madness. Why does this seem heavier than the other one? I don't know. Two Mechanized Madness, so we've got a few of those. Very nice. We got two packs here. What is this one? We have a Legend of Blue Eyes pack back at it again. This is the one. This is the one we've been waiting for. The other ones, they were only playing. This is the serious pack. This is the one with the Blue Eyes White Dragon. Here we go. Red Eyes Black Dragon, Dark Magician, something like that. We've got a Wasteland. We've got the Steel Ogre Grotto, number one. Fire Gorase. We've got the Ray Intibitura. Man-Eater. Fire Yaru. Forenzied Panda. The Fusionist, a classic. And here we go. Will it be our first foil out of L.O.B.? No, it's gonna be a root water. A water with a root, very nice. All right, the water with a root. And now we have Invasion of Chaos. So, so far we've pulled one foil and it was the Seeker Rare Invader of Darkness. So, I would love to change that. I would love to pull something that's not, you know, garbage. So, here we go, Special Collapse. Oh, Jammaheltedurk. I'm just kidding. I was not trying to insult Invader of Darkness. I also didn't mean to call you a Duracane. I'll just keep going. Monju of the 10,000 Hands. Almost a playset, nice. Griven's Featherduster, the Dimension Distortion. Very cool. Spirit of the Pog, very nice. Will it get unbanned? If it's banned, is the Spirit Band?  I don't know. I don't know what's going on. Giga, Gaga, Gigo, very nice. We have a Chain Disappearance and here we go. Anti-Aircraft Flowers. So, if you've got a problem with aircraft, there you go. But that is not a foil. That leaves us with our final pack of the Mystery Box. So, so far that Mystery Box had no pulls. Not looking amazing there, but that's okay. We have a Mystery Pack. Will it be something epic? Let's go. We got Invoked Magellanica and that looks like a pharaoh's servant pack. It is our first pharaoh's servant pack. Invoked Magellanica for those Invoked decks. Very cool. You know I'm definitely playing Alistair at the YCS. 100% happening. All right, let's keep going. Because I have not played Yu-Gi-Oh in months, I would say, at this point, besides like some casual goat duels and like Edison and stuff like that. All right, bubonic vermin. Let's go. The Regulation of the Tribe. So, if you see me at Niagara and you ask what I'm playing, you already know. Let's go. DNA Surgery. Very cool. Drill Insect. We've got the Gamble. Dark Bat. The Haya Boosa Knight. All right, is this it? Our first foil of the day. Will it be the Genzo? Come on, Genzo time. Let's go. Ooh, Mirror Wall. I do love this card. Mirror Wallet. Very cool. Wally, very nice. We like that Super Rare. That is a beautiful one. All right, we got a foil. Not too bad. And the final box of this video. I hope you guys have enjoyed this. Somewhat of a longer video. Shout out to Uber Trading for hooking us up with these at cost, basically, is what he paid, which is, you know, not that much compared to, like, getting much legacy back. So, definitely pretty good deal for us. Plus, he sent that insane giveaway. The Forbidden Chalice. It definitely has an epic story. He had it as a PSA graded card, cracked it out, brought it to me in person. I opened it up, or I signed it. I didn't open it.  So, it has definitely a history behind it, which is pretty cool. It's always fun when there's a specific card that has a history. And it's a lot easier to track when they have a signature on them. So, our first pack. We have a Legend of Blue Eyes. Very nice. It's always funny to see, like, sometimes I'll see my signature other places, like, one time I signed a card for this dude and then apparently ended up on Facebook Marketplace, like, a week later. So, I was like, oh, okay, interesting. Let's see how this goes. Really weird when that kind of stuff happens, but I guess it does. RML, very cool. We got the Dark Gray. Powerification. One-eyed Shield Dragon. The Thirteenth Grave. Very nice. We got the Miserizame. Is it Yame? No! We gotta have the original packs from Miserizame. Yame. We got the Root Water. Fajir. Very nice. Here we go. Final card. Got an Umi. So, Ferris servants had one pack. It got a foil. IOCs had, like, 10 packs. They got a foil. LLBs had, like, 10 packs and got nothing. So, let's see if we can break that streak. Back to IOC. Let's go. IOC. I remember when people used to say that packs out of these were weighed. I was like, guys, there is no way they're spending time weighing Reaper at packs. But, yeah, they definitely don't. A Chop Man. But people actually thought that for a while with the conspiracy. Chaos Necromancer. We got the DNA transplant. The Griffin's Feather Duster. Primal Seed. Gale Lazzard. O'Jama Yellow. Very cool. We got the Mad Dog of Darkness. And finally, will it be the CED? The Balloon Lazzard. All right. Okay. Balloon Lazzard. Okay. Very cool. Definitely looking for a Balloon Lazzard. That's my go-to. What's our deck? A Mechanized Madness. We have a complete Machina deck now. Three sets of every card or three copies, not sets. Okay, next pack. We have a Legend of Blue Eyes. Come on, L.O.B. This is your chance. Just pull something. That's all you gotta do, man. Let's go. We got the Sogan. Very nice. Steel O'Groo Grotto number one. Legendary Sword. Imm Warrior Numero Uno. Green Phantom King. Lesser Dragoon. Mountain. We have the Dragon to Capture Jar. And we have a Spike Cedra. He's not spiked. He's spiked. He is spiking us like a volleyball right now. That is painful. All right. Next up, we have IOC. Come on. We have not had great luck with our pulls today, but there's still chance. One, two, three, four. Here we go. Pack trick. I know some of you guys hate it, but the drama. It increases the drama. Let's go. Chaos Necromancer. Coach drama. Coach drama. Okay. Maybe he's in a drama. What do you guys think? He looks more like, this looks like he is literally the guy from Rocky, except for a goblin. Let me know. Does he look just like Mickey or whatever his name is? Energy Drain. We've got the Dawn Turtle. Grand Maju De Iza. Serpent. Sea Serpent. Warrior of Darkness. Raiyukoki. This is actually a great card if you're playing some zombie old school decks. Stray Lambs. And Gigant is another really good card. But unfortunately, that is not a foil. Okay, we're down to a couple packs. I think we have the random pack and then one more. We have one more IOC pack. So that would be, I think, struck out unless it's in the mystery pack. Okay, IOC. Just one more pull. One more pull is all we ask. Let's do this. We have an Earth. Shit. Dawn Tortell. Tower of the Bell. Fiend's Hand and Mirror. A Hero Emerges. Begone. Nave.  It's talking to you. Heart of the Underdog. Here we go. Compulsory Evacuation Device. A very good card. And this is the moment of truth. Let's go. Krenmaju Day Eyes. Oh man, no. This is officially it. It includes one booster and one rare card. What will it be? Please be a good pack. Please be a good pack. Let's go. Come on. Please be something good. We have the reveal. Let's not spoil it too much. Let's do it like this. Oh, that was pretty smooth. Okay. Whoa, first it is a Cross Souls. That's pretty cool. Look at this. Yeah, so it's literally stuck. Okay, actually came off pretty well. It's that kind of sticky stuff, but it kind of comes off. Trifortress Top, or Trifortress Ops, okay. All right, this is actually a pretty sick pack.  So it's not that old. I think 2015, 16, something like that. So let's just see what we can pull to end this thing. Let's not get that stuff on the mat. All right, one, two, three is what we're gonna do. These feel like Hero cards. They feel very slick. Performapal Thunder Rhino. This doesn't really fit any of the other cards who have a legacy. Magma Dragon, we've got the Deskpot 004. Super Every Samurai Soulbuster Gauntlet. Very nice. The Fiend at Griefing. Age M Chain, very nice. We've got the Moon Mirror Shield. Is it up next? Let's see. Oh, a Secret Rare, El Shaddoll. And Neutilus? I've never seen this Shaddoll card before, or El Shaddoll, I guess. But that is really cool. I'm guessing it's not that great, but it's a Secret Rare, which is, you know, that's a great rarity, and we're taking that. And it's not nothing to think, maybe it's guaranteed supers, that's it in a set. Very, very cool. That's a way to end it. All right, so not the best pulls ever, but that insane hack. I mean, we just pulled three boxes that had all legacy packs, which was really, really cool. So thanks again to Uber Trading for sending those in. The Secret Mystery Boxes paid off. And if you guys enjoyed the video, make sure to subscribe to channel for more epic content, including that 150K special where we open every pack in Yu-Gi-Oh history. Shout out to Choice333, Nightshade Gaming YT, Hayden Jamieson, Squirtle, Hoppus, FlexiBoy, Dizzy, Ernesto DeAnda, Puffins of Doom, TCG Trust of Cards, JTcho, Tomato Juice, Daxter, Tonefo Show, and on his high show, Christopher Ward, Ian Musa, John Nolan, Junior Barting, Mike Nance, Mimic Echo, Seth Fisher, Stanley, Thomas McLean, and Tonesy. Thank you guys for supporting the channel, and I'll see you guys next time. Peace.


Hello viewers, welcome to today's lecture on gas optimization techniques. In the last lecture, in the last two lectures, we have discussed about how you can reduce heat time and how you can reduce miss rate. And today we shall focus on another very important parameter that is miss penalty. So, we shall discuss about various techniques for reducing miss penalty. There exist a large number of techniques, actually this is one of the thoroughly researched area and there are many techniques have been I mean proposed by different researchers. So, I shall focus on a subset of them and try to give an overview of the various techniques. So, these are the various techniques multilevel cache, write buffer, victim cache, read priority over write on miss, sub block placement, early restart and critical word first, non-blocking cache, hardware prefetching of instruction and data, compiler control prefetching. So, these are the various techniques, I shall briefly consider in today's lecture. First let us focus on multilevel cache. So, whenever we go for multilevel cache, we have to use, modify our definition about miss rate. Actually, we have to introduce two terms, one is known as local miss rate, another is known as global miss rate. So, local miss rate actually represents the misses in this cache divided by the total number of memory accesses to this cache. So, let me briefly explain it. You see suppose your first the processor tries to access the L1 cache and if it is not present in the L1 cache, then it tries to get instruction or data from the L2 cache. Obviously, the number of accesses from the L2 cache is smaller and miss rate will correspond to the total number of memory accesses to this particular cache. That means, number of accesses that has been tried on L2 cache that will be used for the calculation of miss rate and total number of misses by the total number of accesses for this cache. On the other hand, global miss rate is the misses in this cache divided by the total number of memory accesses generated by the CPU. So, global miss rate obviously will be smaller for L2 caches and for the first level cache, it is miss rate L1 and for the second level cache, it is miss rate L1 into miss rate L2. That means, global miss rate for L2 cache will be equal to miss rate L1 into miss rate L2. And whenever we add a second level cache, let us see how the equation for average memory access time changes. So, average memory access time AMAT as you know is equal to hit time plus miss rate into miss penalty. Now, if this corresponds to L1 cache, we give a suffix L1, L1 and L1. Now, in this case miss penalty of L1, this miss penalty of L1 is now equal to hit time L2 plus miss rate L2 into miss penalty L2. So, we find here the miss penalty of L1. If we can substitute here, we shall get AMAT for a two level cache will be equal to hit time L1 plus miss rate L1 into you have to multiply with hit time L2 plus miss rate L2 into miss penalty L2. So, this is how the AMAT gets modified whenever we are having two level cache, second level cache. And at lower level caches L2 or L3, global miss rate provides more useful information, because that only shows how many accesses are taking place to that cache compared to total number of accesses. So, indicate how effective is cache in reducing AMAT. That means, how by adding L2 and L3 cache memory, the accesses to those L2 and L3 is getting reduced. So, this will tell that. So, question actually arises, what is the miss rate for L3? Actually, there is a possibility that miss rate for L2 or L3 can be higher than the miss rate of L1. So, who cares if the miss rate of L3 is 50 percent? It may be as high as 50 percent or more as long as it is 1 percent of the processor memory access over, I mean, never benefit from it. That means, if we get an overall improvement of performance with large miss rate of the L2 or L3 caches, it does not really matter. Our overall performance or AMAT is the most important parameter. So, let us consider, let me illustrate with the help of an example. Let us assume that ideal CPI is equal to 1. So, these are the assumptions. So, assumptions are number 1, ideal CPI is equal to 1. That means, 1 cycle, 1.0 cycles per 1. That happens whenever we get a cache heat in the L1 cache and clock rate has been assumed to be is equal to say 4 gigahertz and miss rate L1 is equal to let us assume it is 2 percent. Then main memory access time is assumed to be is equal to 100 nanosecond. So, whenever we have got 100 nanosecond, what is the find out miss penalty without L2? So, miss penalty without L2 will be equal to 100 that is 100 nanosecond divided by 0.25 nanosecond that is 4 gigahertz is the clock rate. So, this is 0.25 nanosecond. So, this will give you 400 clock cycles and obviously, your CPI will be equal to 1 plus since the miss rate of L1 is 2 percent to 2 by 100 into 400. So, this is the overall CPI without L2 cache. So, this is equal to 9 cycles, cycles per instruction that is your 9. Now let us consider the situation when we add when we go for a second level cache. Let us assume global miss rate for L2 cache is equal to 0.5 percent is quite small. So, L2 heat time obviously, will be much smaller than the main memory access time. So, that is considered to be 10 cycles compared to 100 cycles of main memory access time. So, in this case you are getting from the L2 cache and you are taking lesser time. So, L2 miss penalty is equal to 10 divided by 0.25 that is 40 clock cycles. That means, whenever the data is available in L2 cache you will require 40 clock cycles to get the data. So, total CPI cycles per instruction in such a situation is equal to 1 plus 2 percent into 40. So, this is the 40 and plus 0.5 percent into 100, 400 that was the clock cycle that we got. So, 400 now what happens your CPI this becomes equal to 3.8. So, earlier we have seen the CPI was 9 now we have got 3.8. So, the performance improvement is equal to 9 by 3.8 this is roughly equal to 2.37. So, this particular simple problem illustrate how the performance is improving by using L2 cache. So, if you are having only annual cache L1 cache your CPI is 9 and when you have got L1 and L2 cache then your performance is improving by 2.37 times. So, CPI is reducing to 3.8 cycles. So, with this benefit we may say that the speed of L1 cache affects the clock rate of CPU. As we know the CPU is directly communicating or interfacing with L1 cache. So, most of the communication between processor and memory that takes place with L1 cache and that is the reason why the heat time of L1 cache affects the clock rate of the CPU. So, clock rate is primarily decided by the heat time of L1. On the other hand speed of L2 cache only affects the miss penalty of L1 as we have seen by this calculation. So, the L2 cache will reduce the miss penalty and we can have two different policies. One is known as inclusion policy which I have already mentioned in the beginning. So, many designers keep L1 and L2 block sizes same. So, that means the L1 and L2 you can have the same block sizes the number of words number of words that is present in the block is identical in L1 and L2. And if that is not true I mean otherwise that means if L1 and L2 block sizes are not same then there will be several L1 blocks may have to be invalidated whenever there is a L2 miss. So, if there is a L2 miss several L1 blocks may have to be invalidated if inclusion property is not followed. Another alternative is multilevel exclusion in this case L1 data is never found in L2. So, normally L1 I mean includes L2 includes L1, but that is not preserved. So, that exclusion property is violated in some situations. So, that means L1 data is never found in L2 that means and some commercial processors have used this for example, MD Athlon follows this exclusion policy. So, that inclusion property is not used in memory hierarchy. Now, let us consider another technique that is known as use of write buffer. So, write buffer is a queue that holds data to be written into the memory as we know whenever we are writing data into the memory then if it is not in the cache or even if it is in the cache you have to write it into the cache you have to also write it in the main memory to satisfy the inclusion property. So, and to avoid that what can be done we can add a victim buffer what is the role of the victim buffer let us consider the situation of a write through policy. So, in case of write through the data is written into the cache memory I mean without cache miss since it is available in the cache it is written into it and obviously, we will take one clock cycle. And if we use write through policy and without using this victim buffer then the number of I mean CPI will be equal to 1 plus 100 into 10 percent assuming that 10 percent is the miss rate of l 1 cache. So, in such a case you will require CPI of 11 cycles. So, if we this will not be required if we use this victim buffer. So, we can see here the data is written into the cache memory which are present here and then it is also written into the victim buffer and in the offline the data writing takes place in the lower level memory. So, CPU is not concerned with that because CPU has already got the data from the I mean CPU has got it from the I mean from the l 1 cache. So, it is written into it data is transferred and writing takes place in the cache, but it is also written in the victim buffer, but it is done in the offline. Another approach can be used along with this write buffer which is known as write merging. So, addresses of the new data matches the address of the valid write buffer entry. Here what is being done this write merging suppose a particular entry of a block entry of a block is modified. So, this is being modified and this is being modified. So, this is available in the write buffer and you may have multiple words in a single block. So, this data has been modified. Now, there is a possibility that another data is also you are also writing in another data and in fact address of the new data matches to the address of the valid write buffer entry. So, in the write buffer it checks whether it is present in the write buffer. Then what is being done it is you are not writing into the buffer you are modifying it here. So, for that you will require additional valid bit present in the write merging technique. As a consequence you will have valid bit for here, but it will definitely save the number of tags you will have a common tag that is the reason why for the same address you are getting in the write buffer. So, write merging is an extension of this write buffer approach where you check the data in the write in the victim buffer first before you try to read the main memory. And write back policy is much more complex to implement whenever we use write buffer. So, that we shall not discuss in this lecture. Now, we shall focus on another technique which is known as victim cache. So, reducing miss penalty by using victim cache, what is victim cache? So, you have got your cache memory here. Now, in addition to this cache memory you have another small cache memory which is known as victim cache. Why you are calling it victim cache? The reason is that some data add a fully associative buffer to keep recently thrown out discarded data from the cache. As we know whenever you have to replace a particular line you have to throw it out. Now, instead of throwing it out you are writing it into the victim cache that means the which is the victim block to be replaced that particular block is written into the victim cache. So, victim cache will contain the recently thrown out data. So, next time if you try to access it you may get it here instead of reading it from the main memory. That means here we are trying to combine the first hit time of direct map cache. As we know in case of direct map cache the advantage is it is very simple and it is you have got the directly read it from the cache and there is only one word per block. In this case in victim cache what you are doing? You are reading it, you are storing it and then subsequently you can read it from here. So, you add a fully associative buffer to keeps recently thrown out discarded data from the cache and it has been found that a 4 entry victim cache removed 20 percent to 90 percent of conflicts for 4 kilobyte direct map data cache. For example, it is used in decalpha HP machines AMD uses 8 entry victim buffer. That means you have got not only one you can have 8 entry victim buffer and this will help you reducing the miss penalty. So, this is very useful and used in many situations. Let us consider another technique which is called read priority over write on miss. So, we are aware of the read after write conflicts and whenever we are performing a read operation after write this particular approach read priority over write on miss leads to read after write conflicts with main memory reads on cache misses. Normally a dirty block is stored in the write buffer as you have already discussed and usually write all blocks from the write buffer to the memory and then do the read. So, you are writing into the write buffer then all the words of the buffer is transferred to the main memory then you do the read, but instead of that what can be done?  That means you are not performing the write of all the blocks from the write buffer into the main memory you are not doing that. So, in this case if you stall is less since restarts as soon as you perform the read operation. So, this is how you can avoid I mean you can avoid read after write conflicts with main memory reads on cache misses. So, this approach is also used in some processors. Now let us consider another approach which is known as read priority over write on miss. So, a write buffer with a write through that we have already discussed it allows cache writes to occur at the speed of the cache. That means as we have seen it writes into the cache memory and data is also written into the buffer and in the offline writing takes place from the write buffer into the main memory. So, however the so far as the processor is concerned it does not take more than the time needed to write into the cache memory. So, this is the benefit of write buffer whenever you are using write through which I have already discussed in detail. And write buffer however complicates the memory access what can happen they may hold the updated value of a location needed on a read miss. That means after immediately after write you are trying you are there is a you are this may be hold in updated value of a location needed on a read miss. That means after write a read miss is occurred. So, this let me illustrate this with the help of this example.  Now you can see here from r 3 you are writing in the memory and then again from the same memory location you are writing into the in the register. So, you can say this is write and after that you are reading and transfer reading from the memory. So, in this case you are reading data you are write a register content into the memory and then you are reading it here. Now, what can happen by using write buffer this this word is written in the memory was stored in the write buffer data was transferred to the write buffer, but if this read takes place. So, there is a miss here and if you read it from the memory you will get the previous data. So, in such a case you will get a you will not get the updated data. That means the content of r 3 and r 2 may not be same. So, r 2 and r 3 r 3 may not be sorry same as r 2 content of r 2 and r 3 may not be same. If the from the write buffer if the writing has not taken place into the same memory location because these two are referring the same memory location. So, this can happen. So, this may hold the updated value of a location needed on read miss. So, this you have to take care whenever you perform read. So, you have to give read priority of a write on a miss. So, in such a situation you have to take proper precaution. So, that r 3 is the content of r 3 and content of r 2 are identical. So, whenever this type of situation occurs necessary precaution has to be taken. So, this is reducing miss penalty by read priority over write on a miss. So, this is a write through with write buffer read priority over write check write buffer contents before you read. So, if no conflicts let the memory access continue.  So, in this case say before you perform this read operation from the memory you will check the write buffer what is the this value is present in the write buffer. So, if it is present in the write buffer then you if there is no conflict only then you continue the memory access. That means first write buffer content in checked and if it is present in the write buffer you read it from there and write priority over read. In this case waiting for write buffer to first empty and can increase the read miss penalty. In such a case what you are doing you are you are that whatever has been written into the write buffer it must complete writing in the main memory.  So, this is the write priority over read. So, you have to you can you have two different approaches in the first case read priority over write you are giving priority to read over the write into the write of the data that is present in the write buffer into the main memory. But in such a case you have to check the write buffer first before you read it from the main memory. In the second case you are waiting till the write buffer is empty and in such a case obviously read miss penalty will increase because the processor has to wait till the write buffer is becomes empty and data is written into the main memory. So, this is the situation of read priority over write on miss then let us consider sub block placement. So, in this case single word per block requires large number of tag bits as we know if we are having a you may recall the basic organization of cache memory. In the cache memory you have got the different valid bit then you have got those I mean check bits various other management bits read only write only and so on. Then you have got the tag field and here is your data instruction whatever it may be now there is a possibility of having only one word per block. So, as you know you can have only one word now to reduce the size of the tag as you have already discussed you can have multiple words. So, in such a case multiple words on a single block. So, this part will be same, but your number of data words of a single block will be more. So, this is your tag field and you have got multiple words on a single block. So, we find that by you are able to reduce the number of tags required in the memory by having multiple blocks in a multiple words in a single block in a single block having multiple words. So, and also we have seen that we have a single tag field and valid bit field. So, there is a single valid bit field and single tag field that is being shared by all the words in a single block that is what is the situation. Now, in this case this requires load of full block on a miss. So, whenever there is a cache miss as we know the entire block has to be transferred all the words are to be transferred. So, in such a case what will happen the miss penalty will be more. So, what can be done this problem can be overcome by having a valid bit per sub block. So, in this case what you can do you can add separate valid bit here in each of these for each of these words. So, in such a case what can happen you will instead of transferring the reading the I mean instead of loading the full block you can load only a particular word. So, by having valid bits per sub block and that means you will transfer if there is a miss for this you will transfer this. So, this will be one, but the other valid bits may be 0. So, this will reduce the miss penalty by having sub block placement. So, instead of reading the all the words from the main memory you can read only one word and then modify the valid bit, but this will definitely increase the number of valid bits, but the benefit is that your miss penalty will be significantly reduced. Another technique that can be used that is known as early restart and critical word first. So, in this case do not wait for the full block to be loaded before restarting the CPU. So, in this case you are reading these words one after the other because as we know the bandwidth the width of the processor memory bus is usually one word. So, you can transfer read one word at a time. So, you will read one word then this word then this word then this word one after the other. Now, in this case what you are doing as soon as the requested word of the block arrives send it to the CPU and let the CPU continue execution. Suppose the requested word is this one. So, you modify you make it one and immediately you transfer this particular word to the CPU do not wait for the other words to be read from the CPU. So, this is known as early restart and critical word first. So, this is the early restart technique and we shall discuss the critical word first after this. So, this is how you can again reduce the miss penalty, but obviously it will complicate the situation little bit and the processor has to take care of the situation. That means, it has to read the other words from the memory after sending the sending it to the CPU. So, then comes the critical word first. So, request the missed word first from memory and send it to the CPU as soon as it arrives. Let the CPU continue execution while filling the rest of the words in the block and also this is also known as raft fetch and requested word first. So, in this case you are not reading sequentially you are reading the critical word first. So, critical word first that means, if this is the requested word you read this particular word first you can generate the CPU will generate the address accordingly and it will read this word and transfer it to the CPU and subsequently the other words of the block this one this one and this one will be read one after the other and in the meantime the CPU will continue to execution and the miss penalty is significantly reduced. So, this particular technique is also used in some cases and this is particularly useful whenever you have got large block size. So, if you have got one or two words per block then this is not very effective, but whenever you have got a large number of words in a block this particular technique is very useful and special locality is a problem it tends to wait next sequential word. So, it is not clear whether there is a benefit from the early start what you see what we are doing in this particular case we are reading this particular word. This is the critical word and then you may be reading this then this then this, but what the processor can ask for after this word the processor may ask for this. So, again there will be a cache miss. So, the processor will read and word three then word one then word two then word four, but the CPU may ask for word four after word three. So, again this will lead to a cache miss. So, this is actually special locality is being violated because we used reading from sequential locations to improve the special locality, but since it is disturbing the special locality it is not known whether there will be much benefit from this early restart technique. So, this is an example MD Athlon has 64 byte cache blocks L2 cache takes 11 cycles to get the critical 8 bytes to fetch the rest of the block 2 cycles per 8 bytes. So, MD Athlon can issue 2 loads per 2 loads per cycle. So, compute access time is time for 8 successive data accesses. So, you can compute the access time for the 8 successive data accesses the solution is 11 plus 8 minus 1 because 1 you have already read into 2. So, this 25 clock cycles for CPU to read a full block cache for this particular problem. Now, without critical word first it would take 25 clock cycles to get the full block. So, after the first 8 bytes are delivered it would take 7 by 2 that means 4 clock cycles. So, total of 25 plus 4 29 clock cycles are needed in this particular case. So, this shows the access time for 8 successive data accesses. So, if you read the critical word first then this will what will happen. If you read it in this manner this is the time and if you read it in this way 25 plus 4 29 clock cycles. So, this particular example highlights the critical word first reading word I mean the problem that arises whenever you do critical word first. Now, let us consider the case of non blocking cache memory. So, this non blocking cache allow data cache to continue to serve other request during a miss. So, normally as we know whenever there is a cache miss. So, processor is blocked in the sense there will be some weight cycles or there will be some clock cycles that will be when the lapsed before you the processor can resume the execution. So, that is the reason why it is called blocking. Now, if you are having a multi programming environment. So, in such a case if a particular execution of a particular process is blocked the processor can start execution of another process. So, that is what is being mentioned here. So, this is meaningful only with out of order execution processors. So, whenever you are doing out of order execution processor and in such a case this is very useful and obviously this will require multi bank memories and Pentium Pro allows 4 auto standing memory misses. So, even there are memory misses it will continue execution of out of order that means instructions are not executed in order need not be from multiple processors, but here out of order execution is taking place of different instructions. So, the way the instructions are present in the program memory and it will not be executed in the same order and as I mentioned this will require multi bank memories and Pentium Pro allows 4 out standing memory misses and non working cases to reduce stalls on misses. So, in this case heat under miss reduces the effective miss penalty by working during miss. So, heat under multiple piece or miss under miss may further lower the effective miss penalty. This can happen because of multiple overlapping of multiple misses by overlapping multiple misses and significantly increases the complexity of the cache controller as there can be multiple outstanding memory accesses. So, cache controller will become very complex whenever you allow this multiple misses and it will definitely require multiple memory banks which I have already mentioned that means without multiple memory banks this will not be effective. So, the address will be generated and data is available from different banks and then you can read it at a faster rate. So, the cache performance for out of order processors is difficult to define miss penalty. We have been so far discussing miss penalty in the context of I mean the way the instructions are executed, but whenever you do out of order execution out of order processes it is very difficult to define miss penalty to fit in out of order processing model. Processors is much reduced average memory access time and overlapping between computation and memory accesses will take place in this particular situation and we may assume a certain percentage of overlapping. So, we may assume some percentage, but this percentage will vary from application to application. So, in fact is the degree of overlapping will vary significantly and that is the reason why it is difficult to define miss penalty whenever you are having out of order processors. Now, we shall discuss another technique which is known as prefetching and in fact this not only reduces miss penalty it reduces miss rate and the prefetching can be done in different ways. First one is known as hardware prefetching. So, in this case you prefetch both data and instructions. Instruction prefetching is done almost in every processor. This is a very common technique and processors usually fetch two blocks on a miss requested and the next block. So, what you are doing because of special to exploit special locality normally as you know whenever there is a cache miss the entire block is entire block comprising multiple words multiple words and the entire block words are fetched. Now, essentially to exploit special locality. Now, we are going further what you are doing we are fetching more than one block. Although the second block say you are fetching for the first block and also the second block. Although the requested word is present in the first block this is the requested word, but you are fetching this word this block and to the next adjacent block. So, this is known as prefetching. So, processors usually fetch two blocks on a miss requested and the next block and there are several commercial processors like Alta Spark 3 compute strides in data access. So, prefetch data based on this approach. So, this technique may help in reducing the miss penalty because of the locality a special locality. So, next time whenever you try to read a word from the second block it is already prefetched. So, it will not lead to any cache miss. So, this is how the miss penalty is reduced and also it reduces the miss rate because next time miss will not occur. So, it will reduce the miss rate as well as miss penalty. Now, another technique is software prefetching the previous one was hardware prefetching the hardware automatically does it. In this case you can prefetch data load the data into the register as it is done in case of HP power is loads or you can perform cache prefetch loads into a special prefetched cache. So, instead of loading into the register you are loading into a special prefetched cache as it is done in MIPS 4 power PC Spark version 9 and special prefetching instruction. Obviously, whenever you are doing it by software you will require special prefetching instructions. So, this special prefetching instructions cannot cause faults a form of speculative fetch. So, you are doing a kind of speculative fetch that means assuming that a word or instruction from the next block will be required you are doing the prefetching by using special instructions. So, you will require the special instructions are provided for the purpose of prefetch. Then third approach based on prefetching is compiler controlled prefetching. So, in this case compiler inserts instructions to prefetch data before it is needed. There are two flavors one is known as binding prefetch request to load directly into the register. So, must be correct address and register that means whenever we are writing into a register this is a I mean you cannot it is a strong binding and you cannot really change it because it is already in the register. And non-binding prefetch when you are doing into a loading it into the cache. So, this can be incorrect and whenever a fault occurs you may have to discard the cache and you have to reload it. That means replacement has to take place can take place in this particular case, but this cannot happen in the binding prefetch. So, whenever you do prefetching whether done by software or done by compiler with the help of a compiler prefetch instructions will incur these are additional instructions obviously there is an additional overhead. So, what you have to do whenever you are using prefetching. So, these additional prefetching instructions will take will make the execution time longer. So, you have to see whether that benefit that means the loss because of these additional instructions is being matched by the reduction of the miss penalty. So, it is the cost prefetch issues less than saving in reduced misses. So, if the miss reduction miss penalty is reduced because of this prefetch instructions or prefetched data then it is fine. So, this is a kind of trade off that you have to check that means you may not get benefit by prefetching. So, that has to be checked. So, we have discussed various techniques for cache memory optimization. Now we shall summarize them very quickly to give an overview of the different techniques that we have discussed in three lectures. So, first one is simple small and simple cache that has been used to reduce the hit time. However, it may increase the miss penalty and complexity is not much. So, complexity is 0 and avoiding at this translation whenever you do at this translation then again hit time is reduced and it has got little bit complexity. So, complexity level is 2, then third is pipeline in writes. So, writing operation can be pipeline to reduce the hit time and complexity is level is 1, then simultaneous tag comparison and data reading which I have discussed it reduces the hit time having complexity of 2. Then using suitable write strategy write through a write back and we have discussed about the advantages and disadvantages of write through and write back policies and by using suitable write strategy you can have the complexity of 2. That means normally write through is used and with suitable precautions. Then wave prediction and pseudo associative cast that you have discussed which also reduces hit time and complexity level is 2 and then avoiding at this translation that is your virtual cache that also have a complexity of 2. Then you have got various techniques for reducing the miss rate in this case larger block size whenever you go for larger block size the miss rate is reduced. However, miss penalty increases because of larger block size you have to read them all the blocks and complexity level is 0 and then higher associativity you can go for that also reduces the miss rate miss penalty is increased whenever you go for higher associativity because of the complexity of the memory and it is little more complex pseudo associative cases can be used with complexity level 2 to reduce the miss rate. Then various compiler techniques that you have discussed which are used to reduce the miss rate. However, in such a case there is no change in hardware so complexity level is 0. Then we have discussed various techniques for reducing the miss penalty second level cache complexity level is 2 that reduces the miss penalty right buffer it reduces the miss penalty complexity level is 1 victim cache that also reduces the miss penalty complexity level is 1 priority read message as we have discussed has the complexity level 1 sub block placement. We have seen it reduces the miss penalty as well as hit time which has the complexity level 1 and early restart and critical word first has is quite complex complexity level 2 and it reduces the miss penalty non-booking class cache memories that we have discussed which has very which is really very complex. So, complexity level is 3 and hardware prefetching of instruction and data that reduces both hit time and miss penalty with complexity level 2 and compiler control prefetching which is reduces both miss penalty and hit time has the complexity level 3. So, this table gives you the various widely used techniques in commercial processors which are used to reduce the either the hit time or the miss rate or the miss penalty. So, these are the various cache optimization techniques that we have discussed in today's lecture and by next lecture we shall focus on the main memory. Thank you.