A fiery horse with a speed of light, the cloud of dust, and a hardy high old selver, the lone ranger. The years of unrest that followed the Civil War, a powerful secret organization called the Legion of the Black Arrow sprang up in the western United States. Its members were to be found everywhere, defying the law or using the law for their own purposes, working toward the ultimate goal of revolt and the foundation of a despotic empire. It was the masked rider of the plane who led the fight against this band of outlaws and traitors, and for once his great strength and courage, his daring and resourcefulness were taxed to the utmost in the cause of democracy. Return with us now to those thrilling days when the West was young. From out of the past come the thundering hoofbeats of a great horse, Silver. The lone ranger rides again. The lone ranger rode into camp expecting to find Tonto, but when he got there the camp was empty. Tonto and Skult were gone. The ashes of a campfire were scattered and there was evidence of a struggle. With Silver beside him, the masked man's keen eyes searched the ground for tracks. He's gone, Silver. There's no sign of him. All five shells fired from his gun. The embers are still going from the campfire. Whatever happened, it couldn't have been more than a few hours ago. Silver, look at this, hoof prince heading west, steady old boy. After them, Silver, Tonto may be heard or worse. When the masked man started out on the trail, Tonto and his captors were many miles ahead, approaching a spot where the trail turned left, passing the entrance to a blind ravine. At the entrance, the leader threw up one hand. What are you stopping for, Tonto, like that masked man wouldn't let the dust settle under his horse's hoose when he starts afters? I reckon he already has. Silver, plenty passed. Can't you plenty quick?  You men stay with the Indian. Make sure he doesn't make a run for it. He's tied to the saddle and his horse is tied to mine. He won by most. You'd better not. Decker, come over to one side here. I want to destroy the Buffalo Valley wagon train. Buffalo Valley wagon train? There's no wagon train sitting for Buffalo Valley. That's closed territory. The government opened it, Decker. I got information that the first wagon train is leaving Culver City tomorrow. Information where? You know better than to ask that. Oh, that's heavy. The black arrow. Let's sit about that the better, Becker. You and I, the only ones in this group will belong to the black arrow. The others must learn nothing. Kino, their outlaws are being paid. They won't ask questions. Good. But this is your wagon train. You want to stop it to keep Buffalo Valley from being settled, huh? How do we make it for all of them to move into new land in the west the better for us? You'll stay here and keep one man with you. The rest will follow me for the wagon train. What's my job? I want to trap the lone ranger. Easier said than done. This ravine is closed at the other end, Decker. Make use of it. After I'm gone with the others, you lead the Indian into that ravine. Yeah. Tie him well back from the entrance. Leave a plane trail so the masked man can see him when he gets to this point. So far, I got it. When the masked man goes in to free the Indian. In the jet with me starts slinging bullets, eh? No. No. Now shoot. I want to delay the masked man so he can't help that wagon train. Besides that, I want to capture him alive. If you can. That'll be up to you. I think you can figure out how to do it. Well, the ravine's got pretty steep walls. This entrance is narrow. Do it in your own time. The rest of us can't wait. All right, man. Slack, you stick here with me. We're looking after this engine. Whatever you say, Decker. The rest of you come with me. That wagon trains a long way from here. We'll have to step along. We take the trail toward Culver City. Look, you still ain't told me how we're going to corral a masked man in this here blind ravine. If he gets in, make sure he doesn't get out. Huh? This pass is narrow, Decker. You've got blast in powder. Use it. Adios. Come on, you men. What was he saying, Decker? I didn't say anything. I didn't know, Slack. Blast in putty and now pass it. Well, I gravy sure that's it. Come on, bring that engine along. By the time the mask vent comes this way, everything will be all set for him. Get out of here. The tracks are still clear. We're on the trail of silver. Otto can't be hurt. He's made his count traveling the soft ground as much as possible. He knew we'd recognize his hoof prints. We'll find them, old fella. Sticking to the Culver City trail. Turns left here past this ravine. Silver! Horses split up. Most of them kept on the trail. These three turn into the ravine. Scout is one of them. Come on, silver. That means Tonto must be. Silver! There he is at the far end of the ravine. Tonto! Hide and gag. This may be a trap, but we can't stop. Come on, silver. Into the ravine. Has the masked man raced the stallion into the narrow ravine toward Tonto and Scout? The two bad men lay flat on the rim of the rock above the entrance and watched him pass. It's working out just like Toloch figured it. Get rid of that blast and putter slag. All set, Dekker. I'll let you know when. He's passed us all ready. Let him ride a good ways. Let him be cleared up to the red skin before we set it off. He's sure riding for a big surprise, ain't he? Unaware of danger, the masked man rode straight to help Tonto. Galloping straight across the floor of the ravine, he pulled up beside Tonto. Kimusabe, you're not hurt. Wait, I'll get that gag off so you can talk and these ropes. Kimusabe, this trap, you ride. Ride quick and get out. Not without you, Tonto. No, you hurry. Only one way out of the ravine. You're not bothered. Ropes take too long to get cut. Scout all tied up. And there's one rope. Now this one. There. Scout is free now. Come on, wait. Oh, too late. Here's Tonto. The entrance is piled high with rock. It's impossible to climb over it. Ah, no way out of ravine now. All day long, the Lone Ranger and Tonto rode around the floor of the ravine looking for a possible way out. But they could see none. And by sunset, the two outlaws watching from the rimrock were satisfied they would have no trouble keeping them prisoners. They gave up looking for a way out, Slag. I reckon they know my now. There's eight no way out. Yeah. Give me a hand with this saddle. What? Come on. I got a saddle. You're leaving? Yeah, why not? Still, you're wondering. Oh, Dinker, I don't have any. You won't have no trouble. Give me that bridle. You're leaving me alone? Why not? The two outlaws can't make any trouble. They're safe as though they were locked in the calibou. You just keep an eye on them. Where are you heading? You've been eating local weed. What do you think I'm heading? The Culver City Slag to tell Tonto like we got the Lone Ranger right where we want him. Get him. Get him. Here's the wagon train. Six wagons. When I get on the trail, we'll tag along after them. I'm taking care they don't see us. What the, who's that? It's just... Dinker, what are you doing here? I figured you'd be out this way as soon as I heard the wagon train was camped inside a town. I met another wagon outfit heading this way and got my directions. Why'd you leave the ravine? Because it wasn't needed. You don't need slack there either for that matter. Mask man? Give me the inch of bull. That blast shifted the rock right down and sealed the entrance off. They're penned in, mister. Well, that's fine. Fine and dandy. I reckon you'd want to hear about it. Sure, there's no chance of anything going wrong. You can brand me for a maverick if anything could. You know, Decker, good work. I thought you might need an extra hand here. That wagon train won't be so easy to stop. You know my plan. Sure, but I... But nothing. It'll work. They'll make camp at Blue Run, right? Right beside the spring. It'll be as easy as pulling a cinch. I reckon so. And now that you're here, I'm going to leave things in your hands, Decker. You will take charge and I'll go back to... Hey, what's that? That wagon I was telling you about. The one that's joined in the wagon train. Yeah, passing right by us. No need for any of them to act unnatural. We ain't known to be outlawers. Yeah, that's so. Just act friendly, gents. The one that's heading for Buffalo Valley? You're joining it? My husband and I have been hanging for a long time to get out that way, haven't we, Bill? Sure have, Harry. Of course, we've never been to Buffalo Valley, but that don't signify... Any of you gents ever been there? Yeah. Yeah, some of us have. You going along? No, we're not. How's the country out that way? I hear it's right good range land. Well, that's a matter of opinion. What's wrong with it, mister? You don't sound overly enthusiastic. It's no land for settlers. Why, we heard just the opposite. Full of bare mountain lions. Cold in the winter and hotter than a stove lit in the summer. You won't like it. Well, we... We sort of had our hearts set on it. It'll break your hearts. You want my advice, turn back. Turn back? That's what I'd say. I don't know what to say. Rain up there, Abby. Mister, I don't know what your reason is, but it looks to me like you're doing this deliberate. You've got some sort of stake in keeping people out of Buffalo Valley. Why should I have? I don't know. But you're certain it's your act that way. Let me tell you this. Our minds are made up. And I reckon the same goes for all them folks in the wagon's yonder. So you can save your calamity howler for folks that are scared of their own shadows. We ain't. Hello, mister. Get up there. Looks like he didn't swallow it to a lurky. You never mind. You wish he'd listened after what happens at Blue Run. If he's alive. Yeah, if he's alive. Yeah, before that wagon came along, you were saying you wanted me to take charge. I do.  Yeah, Decker. I want to make certain that mask man is as much a prisoner as you say he is. Don't fret about that. I'll bet him and the engine have given up already. I can just see him sitting there in the ravine right this minute feeling sorry for themselves. But Decker was wrong. For the Lone Ranger was busy in the ravine working desperately in the darkness. You see that tree poking out from the rim above his tunnel? It's outlined against the night sky. Uh-huh. Just give me your lariat. I'll try to sling a loop around the tree. Oh, yeah. If I succeed, we can haul ourselves up to the rim rock. There's only one guard left up their tunnel. We can deal with him easily. Ah, you throw rope. You've got him. You put rope on branch. It's good and tight, Kimosabe. I'll go up first. I can brace my feet against the rock. Maybe branch break. You'll have to risk it. It holds me. It will support you. Here I go. Bracing his feet against the face of the rock. The Lone Ranger went hand over hand up the rope till he gained the rim. Then Tonto climbed the rope to the top. What do you do now, Kimosabe? Follow me, Tonto. The guard must be sleeping beside that campfire. He goes out long enough for Culver City for a reason. We're going to find out what their plans are so we can go after them. Ah, that good idea. Zoom me up, Kimosabe. What is it, Tonto? Silver and Scout. They still down below and ravine. How we ride after outlaw without horses. Leave that to me. But we need Silver Scout. Leave it to me, Kimosabe. We get out of this trap and I think I know how to get Silver and Scout out. Now follow me. The curtain falls on the first act of our Lone Ranger story. Before the next exciting scenes, please permit us to pause for just a few moments. To our story. The Lone Ranger and Tonto escaped from the ravine by roping the branch of a tree and pulling themselves to the rim. Once at the top, they went swiftly and quietly to the campfire with the guard lay sleeping. They worked silently for a few minutes and then had a whispered word from Tonto. Kimosabe, we got powder charge already in rock. Like you say, we light cues now. Not yet, Tonto. First I wake up this guard by putting a bullet alongside his boots. What's going on? Who shot them? They'll make a move for your guns. The mask man. What in blazes? I put a bullet into the ground. I wake you up. How'd you get out of the ravine? We climbed the wall. Climbed the wall? You couldn't climb that wall. It goes straight up. They threw a rope around the limb of a tree and pulled ourselves up. So that's it, huh? I told Dekker you were a smart hombre. I told him you ought to stay. Where has he gone? He left, mister. I know that. Where is he meeting Torlock? I don't know. We haven't time to waste. Where are they meeting? What do they plan to do? Hey, easy with them shooting iron. Speak up. I tell you. Jumpin' coyotes, mask man. Them bullets almost hit my boots. For the last time. All right, all right. I'll tell you. I'll tell you. Holster them guns. Dekker went to meet Torlock at Culver City. There's a wagon train heading for Buffalo Valley. Go on. That's all I know. Go on. Well, when the wagon train makes camp at Blue Run, Torlock figures to... Figures to... Yes? Well, the wagons will be campin' a circle. There's hills all around. Torlock plans to have a freight wagon loaded with kerosene on the slope. Come midnight. Well, he's gonna set it on fire and let it roll right into the wagon train. Oh, that'd be plenty bad, Kimosabe. Kerosene's scouting all over, burnin' up all wagon. Well, that's his scheme. Tonto, get busy. Uh-huh. You do it. I'd take you along as a prisoner. Turn you over to the law. The reason I'm not doing it is because you can't keep up with Silver and Scout. We'll have to ride fast to make Blue Run in time. Uh-uh-uh, Kimos, I'll get out of this section fast. Wait a second. Well, you can't get there in time. You and the engine got out of this here ravine, but you can't get the horses out. Can't we? Just listen. All right, Tonto. Light the fuse. Uh-huh. He liked it. Light the fuse? For what? Well, you were sleeping. We took some blasting powder and set a charge into those rocks. You blocked up the pass into the ravine. Now we're blasting it open again. Well, I was sleeping. Well, if that don't... He was happy. Is the entrance open? Uh-uh. Rock Hall cleared away. You listen. Here's Silver. Here, boy. Stand here, Silver. In the saddle, Tonto. And where we go? Head for Blue Run. We've got to save the wagon train. Get them up, Scout. Come on, Silver. Rain up. What? Rain up, I tell you. What are you doing here? Aren't you guarding the mask, man, the Indian? Because they ain't there to guard. What? Yeah, Mr. Torlock. They got out. The Masked Gent figured a way out. They're heading for Blue Run. But they're horses. They got their horses, mister. They climbed the ravine wall and blasted them rocks away from the pass. They got their horses and they're all gone already. Blue Run, eh? We can't possibly catch them. Not unless you ride a hurricane, you can't. Well, Decker will stop them. Yeah, mister. Maybe so. But just between you and me and these here coyouses, I'd hate to be in Decker's boots right now. That Masked Gent means to save the wagon train. And when his mind is set on something, then, mister, look out for fireworks. We're coming tonight, Camp Bill. Reckon so, Abby. John is the hills. That's Blue Run. We can't buy the spring? So I've been told. A nice, clear drinking water there. Oh, we could use some. How many more days to Buffalo Valley? Not more than a week, according to the leader. Here's your camp! This is Camp Bill. The leader's singing out orders. Circle the wagons! Circle the wagons! We swing around this way, Abby. Get up there, horses. We have cabin for the night. Get up there! Crouch them wheels and swing close. We'll be right beside the spring, Abby. Yep. Nestling right in the hills. What's that for? I was just thinking, Bill. You recollect those men we met just outside of Culver City. The ones who said we were making a mistake joining the wagon trains. Yep. They said we'd have plenty of grief getting there. Well, that's what I'm laughing about, Bill. Those men were so all fine, gloomy. Boy, this has been the pleasantest, easiest trip I ever took. What could happen to us now? A chance. That's a wagon train. Wagon's on swinging into a circle. Nice and snug for the night. And all ready for us to sit on fire. This is going to be easier than shooting prairie hens. Get the wagon with the oil already. Ready and waiting right yonder. Got to keep with the branches and leaves, eh? Just like you said. Couldn't be spotted a dozen yards on. All we got to do is point her downhill, set the torch to the kerosene and let her roll. She'll hit them waggers like a stampede in her. Those campers' tops will be blazing before they know what hit them. Be plenty of light for us to pick them off with the rifles. Yeah, we'll see them clear against the flames. When do we start a rolling? Not yet, Judge. When? Not yet. We'll wait till the middle of the night. We'll wait till that camp is all asleep so there's no one to give the alarm. The middle of the night, eh? We'll be ready. We ride plenty of fire, Kimusavi. All day, in the night. Blue run can't be full, Tutto. Wagon train not know what happened. Maybe it happened already, eh? Keep riding. We come to hills now. Look there, Tutto. Up ahead, fire. Kimusavi, we too late. Outlaw sent fire wagon into camp already. Yes. Blue await, Tutto. That's what it looks like at first. But we're in time. That's the campfire. See? The wagons are around it. Or lots of men haven't struck yet. We're in time. Ah, and what we do? Circle up into the hills above the spring. See if you can locate the outlaws. Ah, me do it. I'm riding into the camp. As soon as you learn anything, ride in and report. Me, Sammy. And you, Kimusavi. Come on, Silver! Where can we... might as well turn in, Abby? The rest of the train sounds asleep. Sure is peaceful, isn't it? Uh-huh. Nothing around us but the stars in the sky. Quiet and empty space. Abby, there's nothing like the west. Nope. If Buffalo Valley's anything like this, we'll write to our friends back east. Get them to come out here. They'd like it. The air is so clean and sparkling. It's the place for folks to live and grow and... Reckon, I'm talking too much. Come on, Bill. Yeah. Guess we'll sleep easy tonight. Nothing to worry about. Guess where you're wrong, mister. Only days. I'm talking, nation. Who's that? I'll reach for your gun. I'm a friend. A friend, huh? How'd you get so close without making a sound? Come into the light of the campfire. Let's see your face. Bill, he's wearing a mask. An outlaw. Don't touch that gun. Who are you? What in blazes do you want here? One shout from me and the whole camp will be roused up. Who I am doesn't matter. What matters is that your lives are in danger. From you, huh? From outlaws. What else but an outlaw, you? Listen to me. You can't see beyond the glow of your campfire. And up in the hills above us is a band of outlaws. They've been waiting for this wagon train. They mean to set it on fire and massacre everyone in this camp. I don't believe it. Wait, hold on, Abby. Mister, you're wearing a mask. And you come out of no place. But, well, somehow, what you say has got the ring of truth in it. If there's any such scheme being... That's a signal for me. Bye. Well, you call and do, masked man. I don't... A ninja. Charlie, give us a beat. What did you find? Me find bad men. They got wagon with kerosene already. They up on hill to west. How many? Ken, maybe more. A ninja has been scouting for you, mister. Yes. Now, listen to me. There isn't much time. I want you to wake up every man in this wagon train. Go as quietly as you can.  Yeah, mister. What about you and the engine? I don't know. I'll ride up into the hills and do what we can from that direction. Here's what you men in the wagon train must do. The camp is quiet, Jacob. Looks like they're all asleep, man. Yeah. Time to get started. Let's take the branches and leaves off the wagon. Hurry it up. That's the last of them, Decker. Kino, now roll that wagon suit over the slope and point the street down where the cabin wagon is below. That's it. Hold it there. Look at this. Let me have with this rope. Hold that wagon, tongue back, and we'll tie it down so the front wheels won't move out of the right direction. Kino. That's it. Pass it down secure. Open the barrel kerosene. All right. Spill it all around. All right. Now, Gents, get in your horses and stand clear. As soon as I set the torch, pull out that branch. Just keep it up from rolling, Wilkins. Yeah. And everybody ride down after it.  Here goes the torch. Pull out that branch. She's blazing it. What in thunder? Who fired that shot? I told you not to shoot. I gave the word. Wasn't us firing them, Decker? And who did it? We fired those shots. Come on, tunnel. What in thunder? The mask man. Hold it and throw it out of the wagon. Everybody run away. Get them out of your way. Decker. It's men from the wagon train. Shoot. Shoot it out. Firstly, the outlaws tried to defend themselves, but they were outlined against the flames. Easy targets for the men from the wagon train led by the lone rain here. In a few minutes, the outlaws saw how useless it was and the fight was over. Don't shoot them, boys. Don't shoot. We surrender. Hold on. Your gun. We got every last one of them, Mask Man. He surrendered. The only time he was getting ready to burn you out, you were hidden in the woods watching this. Harris, I think you can handle these men now, can't you? Mask Man, you just leave them to us. I reckon we'll see they get what's coming to them. Decker, there's one thing I want to ask you. You hold the cards, Mr. Where's Torlock? That's what I don't say to you, Mr. He went back to the blind ravine. I'm sorry to get out of it. We climbed out. You climbed out. Never mind, Decker. The only thing that matters right now is Torlock. I know we've got a ride. We're going now. Right now. Howdy, Ossie. Get him up, scoundrel. Mask Man, hold up. Wait. We haven't thanked you. Why, he's gone. He's gone. We don't even know who he is. I can tell you who he is, Mr. We should never tag him with him in the first place. Otherwise, we'd never been captured. That tears a lone ranger. Far from ravine, Tutto. I don't think we'll find Torlock there. He must be gone by this time. Torlock, him black arrow. Him slippery like snake. Yes, Tutto. Him a zombie. Somebody shoot at us. Tutto, look. At the top of that ridge. That man on the soil horse. Ah, that Torlock. Torlock of the black arrow. Never mind the bullets. Get after him. Him stop shooting. Him ride horse down on the side of the ridge. After him. This is our chance. Come on, old fella. Watch out, old Sue. Who just heard is a copyrighted feature of the Lone Ranger Incorporated.


As a party, we did put an update for the three provinces, that is Northwestern, Western and Southern Provinces, for us to start receiving applications for those ones who are SPAS members of parliament, as well as country chairmen and councilors. The reason is very simple. We have ten provinces. And I think you are aware that we have only three months in between for us to vote for elections. And by May we will be able to start filing nominations. And we want to lessen pressure on us. And we will start an adduction for the three provinces by mid-match. So by end of match, we will be able to announce to the nation people that will be adopted. Then after that, but I think that by mid-match, we will now put an update for the remaining seven provinces. And we expect to announce the candidates by mid-term. That's how our program is. And how has been the response so far? The response is very overwhelming. But I think by next week, it will start making a commendation. So we expect the Central Committee to meet by the end of the month or first week of match. To now adopt the candidates for the three provinces. But I want also to say that we have a Central Committee at the weekend. And that's where we are going to make a decision or set a date for the general conference. So that's one of the decisions that will be made on Saturday. And then we are going to look at many manifestos that will be launched before we start the conference. The Central Committee will deliver it on that to work with the seven document. And also this week, we are going to deliver it on the issue of Youth Journal and Western Promise. I'd say that it's going to be an issue. It's going to be better at the weekend. I would like to find out where are some questions that we have called on the ECZ to call for a stakeholders meeting. To decide on how the campaign strategy is going to be implemented. What is your position as the leader of the group? First and foremost, Electoral Commission of Zambia from the Red God have been inviting all the stakeholders including us to inform us on their preparations for the coming elections. But I think I agree with them that us as a party, we are ready for a discussion with Electoral ECZ and the other stakeholders. So as we are ready, because it is important that all of us can move as one. We want to talk to you as soon as possible. Explosive. Explosive. Come on. Come on, sir. Yes. Where are we going? Kind of, please. No, no.


Multiple award-winning actress and filmmaker Inie Edou is celebrating 20 years in the Nigerian film industry. She has penned a heartfelt note of appreciation on Instagram reflecting on how she started acting as a teenager. The actress however promises to not stop improving on herself and her career counting on the continued support of her fans. Hello, hope you enjoyed the news. Please do subscribe to our YouTube channel and don't forget to hit the notification button so you get notified about fresh news updates.


And today we are going to discuss the technology components that we have been only peripherally noting down. So primarily our concern will be the storage devices, the processing devices or the processors or CPUs. Some of the storage devices are called peripheral devices like the disk and the tape and the mouse and the keyboard and the monitor and such things. We will not spend too much time on discussion of peripheral devices now although I will give you references later so that you can look up the peripheral device. The most important peripheral device which is not really a peripheral is the storage device or the disk because in information systems much of our information resides in this. So we shall be looking at the disk in a bit more depth. We shall also very quickly look at the storage hierarchy that a computer system presents and of course whatever information you store in whichever portion of the hierarchy it has to be processed. So we need to understand a little bit more about the processing capabilities of a computer and what does it mean to us in terms of information processing capability because a computer processor does basic instruction execution at a certain phenomenally fast rate, billions of instructions per second kind of thing. But we are worried about how our information is processed that is relevant to us the business information and how do you translate or correlate the information processing requirements of our kind with the computer's innate ability to process information. So in short we are going to look into inside the computer now and see what exactly does it hold for us although we will be discussing technicalities which pertain to you may call computer architecture something like that our emphasis is not to understand most certainly not the electronics of the computers but also not too much about the intricacies internally but what impact do these technologies have in terms of information processing. So in the first session we will discuss the storage device mostly the disk and in the second session we will discuss the main memory and the processor architecture which together make the computer's box. So firstly any storage of information how do you classify the storage could be a variety of kinds so you can classify it based on the speed with which data can be accessed data is stored somewhere and how quickly can you access that data and then cost of storing the data per unit of data. And finally the reliability how reliable is the storage will the data be lost if power fails or if the system crashes what happens if the storage device fails the physical device failure because in any information system you cannot afford to lose data. So before beginning before continuing with this discussion let me ask you some questions from your knowledge of common information storage that you and I come across look at our physical library we have books stored there okay with what speed can you access a book so you are locating let's say book on databases so you go to the library so what is your search mechanism there are what about more than a lakh of books right 100,000 200,000 300,000 whatever be the number so surely you don't start searching from rack A and rack B and rack C so what do you do yeah so you have a classification number or an accession number what would how would that help the accession number will actually point to a particular rack or a place where that book is but the point is you have to know the accession number let's say you know that there is a book by Kurtz silver shorts and Sudarshan and database you don't mug up the accession number as IBM 147 315 what whatever how do you find that so you do a search and you do a search on what on a catalog or a so basically you have in the old style libraries you will have card decks modern computerized library you can do a search on the computer but if you have a card deck usually you will search the cards by title or by author and once you identify a particular book you find the accession number you find the place and then you do what then you go physically to that rack and then you take that book out so without this indexing mechanism you will agree that it will be impossible nearly to search a book you only searching the book throughout the semester if you take let's say 15 seconds to take out one book and see whether you that's the book you want or not you can divide 3 lakhs by 15 seconds and find out the number of seconds required and number of hours impossible essentially then indexing is a key thing whichever be the storage mechanism how do you calculate the cost per unit of data in case of physical storage of books there are two things now here the physical book itself occupies a place in the library rack so the total number of racks plus the cost of the building in which the racks are housed and the total number of books that will give you on an average storage cost per book is so much there is a capital investment in that building and racks and there is a operational expenditure on running the library so if you're a portion that entire thing for the operational cost for the let's say just storage can approximately get so much money it will cost the originally the cost of the book itself is at cost consider information searching nearer home each one of you would have multiple notebooks in which you will take notes or something you'll have notebooks belonging to let's say a previous semester and you would have recorded something somewhere so have you calculated the cost of storing let's say one notebook full of information in terms of bytes how many bytes can you write in a notebook take one byte to be one character counting blanks on one page how many bytes can be written how many characters nobody has done that kind of calculation so that is the cost per unit of data what is the speed with which data can be accessed imagine that you have notes for this session taken on one of the notebooks and you have let's say ten such notebooks and you have to appear for a surprise quiz or something like that and you are searching or an exam so first you'll have to identify that particular notebook which contains this so long it may take only ten that moves in the worst case you do a serial search in about a minute's time you'll be able to access that one within that notebook how will you find out where is the material for this session or if it is not this session but on a particular key where you are searching like schema design or something how will you find out within a notebook flip pages please remember that very rarely do we organize our own notebook with indexes although many of the notebooks provide for that first page index but we do not write you know this is the topic this is the page number this is the topic is the page that is because we can quickly skim through the pages and figure that out but what is this what is the time that is actually required suppose you want to locate say information about normal forms in your hostel room so about a minute to search for the right notebook and another half a minute or one minute to go to that particular topic so about two minutes time is that fair judgment okay what is the reliability there's no power failure for notebooks but I may lose my notebook okay or there might be fire in my room all notebooks may be bird so the the data loss that that we can call it a system crash system crash means or book is just lost or soil it falls into a bucket of water I remember one notebook was put on a bicycle carrier by a friend of mine this happened 30 years ago and when he came out there was no notebook on the bicycle a cow was eating that note we jokingly told him that his notes are liked even by the cow but he said what about me my notes are gone so all kinds of funny things can happen in life how do you safeguard against them notebook is not a very good example because there is a natural safeguard my friends notebook so since there are typically 30 40 students attending a class if I lose my notes I can always depend upon somebody else's if nobody has the notes available there is a textbook on the basis of which I can sort of reconstruct them so you solve the problem of data loss in real life by ensuring redundancy what is there is no redundancy somewhere your identity card for it you lose your identity card take the case of even IIT Bombay you lose your identity card so what happens the immediate implication if you are not well you go to the hospital they may throw you out if you want to go into the lab and suppose the watchman asked for identity card you can't get in you need an identity but identity card can be replicated because the original identity cards information is maintained somewhere else as a backup so from that backup your identity card can be restored it's one piece of information in general you will then agree that if I want to characterize the storage I must worry about the speed with which I can access data the cost of storing that data and the possibility of loss of data and ideally what I would like ideally the speed with which I can access the data should be instantaneous ideally the cost per unit of data should be miniscule and ideally I should have an arrangement such that my data is never lost I can always reselect it of course if the original copy is lost I understand that there will be some time I will have to spend in reselecting we saw that when in case of a disk crash how do you recover using log records and so on so on it is in the context of these three questions that we shall examine the storage hierarchy inside the computer please understand that as well the computer and its storage and peripheral devices are concerned the company is not worried about whether your data is about roll number and marks of students or whether it is your account number and balance it doesn't care the computer recognizes information storage as series of bits zeros and ones organized in a certain way and the computer technology will worry about the accessing of those bits or bytes so no interpretation is a show me interpretation is your problem but accessing the required data at what speed can you do that what is the cost of storing that data bits and bytes and in case something happens to the storage what is the way in which you can recover that data we have to now map the bits and bytes into our meaningful information and figure out how much it will take for us to access the data cost of data etc this is just the background first in terms of computer storage we discriminate between volatile storage and non-volatile storage since the computer technology is electronics we speak of electronic storage as volatile storage if the contents are lost when power is switched off invariably the main memory of any computer system falls under this category it's a volatile store you switch off the machine the contents are lost you switch it on again the contents are non-predictable unless you push something into that memory again the memory contents meaningless things clearly the volatile storage is not suitable for our information processing needs from a storage perspective long term story the long volatile storage is one where the contents will persist even though the power goes off this will include secondary and tertiary storage as well as what is called battery backed up main memory so as I said main memory is something which is definitely volatile storage so this is called primary memory the secondary and tertiary memory are pieces storage which are non-volatile so in case the main memory contents are lost you will always use that secondary or tertiary memory from which you can get the data back into the main memory sometimes you do require main memory itself to continue to contain what you want what you needed in which case you will provide a separate battery backup so even if the main power is lost the battery backup continues to have the same date and this is because the electronic memory today essentially built of what we call flip flops which can store zeros and ones electronically when the power is switched off those flip flops lose their state so there could be zero or one in old times and the main memory used to be made of magnetic core the magnetic cores once magnetized either this way or that way would not lose their magnetism even if power is switched off so the magnetic memory used to be non-volatile the main memory is volatile to that extent this is the storage hierarchy the hierarchy is actually described in the in order of the time that it takes to access information inside that memory the fastest from that perspective is called the cache memory the next faster is the main memory slower than that main memory is the flash memory slower than flash memory is the disk slower than the disk is the optical disk and slowest are tapes so this is the storage hierarchy in this hierarchy cache and main memory are volatile storage all other hierarchy pieces are non-volatile so ideally I would like only desks or flash memory or optical desks or tapes to use for an information system perspective if the last four categories of the hierarchy are non-volatile then the question naturally would be why the head we use these kind of memory at all then what's the fun in having volatile memory if I'm going to lose memory the problem is that the way the computers are architected traditionally the one I'm on architecture which was originally proposed in late 40s you always have a combination of memory and processor memory and central processing unit together forming a computer and the memory which is called the main memory along with the CPU would be live only if there is power there's no power neither the CPU nor memory is required to function that's how the computers have been architected so consequently if at all you want to use computers to process your information your information being on non-volatile storage does not help unless that information can be brought inside the computers man and computer cannot process any information on desk or anything else computer can process only that information which is inside the main man so to constantly bring information from non-volatile storage inside the memory push it back etc. etc. and that is why the cash and men memory are important we shall see the distinction between cash and men men memory later in the second session when we discuss the memory hierarchies along with the processor and look at the computer architecture in this session we are going to concentrate on this which is the main state of our storage systems here is another way of describing storage hierarchy primary secondary and tertiary I use these terms some time ago the primary storage is the fastest media but is volatile so that comprises of cash and men memory the secondary storage is next level in hierarchy it is non volatile it is moderately fast excess time but much slower than the main memory or cash the secondary storage is almost always called online storage online storage means it's something which is physically connected to the computer always so whenever you switch on the computer not only the processor and memory man memory starts working but any online storage typically at desk is always accessible just like in case of a PC where you boot the PC the operating system gets loaded your access to your disk drive all directories etc. etc. the tertiary storage is also non-volatile it has slow access time and it's called offline storage typically a floppy drive or a CD would be a tertiary storage or a tape because that is not ordinarily located inside so when even if you switch on the machine the storage is not accessible immediately unless you go open a cupboard pull out a CD push that CD in till then it's it's somewhere else it naturally has an impact of that time to access information some information is on CD and not on the list you can't access it immediately unless you go and bring out that CD and push it into your computer so online storage offline storage both refer to non-volatile storage but they differ in the access time and primary storage is cash or memory the other three categorizations is a schematic diagram of a disk drive so what you see on the right here is called the arm assembly these are magnetic heads you will notice that this magnetic head is seen here but what you don't see is the magnetic head which is actually meant for the lower surface of the top disk the lower surface of the top disk because that lower surface also magnetic then you have another disk here again there is the upper surface lower surface another disk here how many such disks can you have all of these disks are put on a single spindle there is one lacuna there of course that all the disk will rotate exactly at the same speed there is no difference secondly now you can just say go to tack number so and so and sector number so and so because now there is this number also how do you identify the disk number the disk itself has two surfaces so you may call disk one surface one disk one surface two disk two surface one these two surface two etcetera alternately because there is a magnetic head on each surface you may simply number the heads head one head two head three head four head five head six head seven as many heads that you have and and that will give you exactly which disk you want to read the problem with this arrangement is that suppose I want to read let's say something from track five on the first desk and then after that track 28 on the second desk now when I am reading track five on the first desk all the other heads are also exactly on the track five of the corresponding this it makes much more sense then that when I write information rather than writing it or reading it in arbitrary track numbers and head numbers suppose I say that I will read on a given track on all the days or I will write on all the days of the same track what will this save from the reading writing time the moment of head across the tracks because once a particular head is positioned on set fifth track all other heads are also positioned on the fifth track of the respective surface okay secondly in a single rotation of the desk all the heads which can read and write independently can be writing simultaneously consequently I get lot of parallelism so if I have let us say five days five days will mean how many surfaces in surfaces and it says certain capacity x bytes of a track then I can write 10 x bytes in a single rotation on the track consequently all such simultaneously writeable single track can be assumed to form what is known as a cylinder so if you take those of you have done engineering drawing can imagine that if you take a cross section of all the desk you you see a cylinder okay so this cylinder this is the kind of cylinder that you have how many surfaces the cylinder have this is the first surface second below this third fourth below this fifth six etcetera if you have five days a cylinder has ten sort of tracks inside it okay so now the tracks are you are you are now talking about a track T here however there is a surface one surface two surface three surface four etcetera and it makes sense to read or write one cylinder full of information because once you move the magnetic arm on top of a particular track all the tracks within that cylinder are aligned with the corresponding arms so consequently you can read or write information very fast this is exactly how a disc drive works in the very early days of computers when such disc packs were made these arms could withdraw back and this entire spindle with its cylinders could be taken out so these were called actually removable disc packs just to give you some idea of the cost the first online disc pack that we had was on a machine called EC 1030 which we got in 1974 in IIT in late sixties these were introduced by IBM mainframe machines the capacity of a disc pack was they were I think five four deaths or five days there the capacity of a disc pack was 7.25 megabytes find it laughable but that was a very large storage on 9 to 7.25 megabytes was the storage the disc pack used to be very heavy if I lifted it it would take some the disc drive itself was roughly the size of this table and the disc drive cost was five lakh rupees and the cost of a disc pack was 56,000 rupees 7.25 megabytes so you put it inside and that was the early disc storage okay the most of the storage used to be on magnetic tapes but magnetic tapes were sequential devices as we shall see the point is that even though those devices were costly that day they were preferred for information processing because they permitted direct access and we shall be spending some time on what it means of direct access in terms of our information is this mechanism clear anybody has any doubt on this mechanism she basically move the arms up and down on this and then as it resides on a particular track you can read or write on all tracks of the so-called hypothetical cylinder that is formed by the same number of same track number on each of the surfaces. Yeah sorry this are all tied to this spindle when the spindle rotates all this moves simultaneously so if this disc is rotating this is also rotating this is also rotating all this rotate exactly they are like a rigid mechanical combination. No because there are two different arms this is one arm and this is also another arm so this arm is accessing information from the magnetic coating on the top surface this arm is accessing information the magnetic coating on the bottom surface so both surfaces are accessible and there is an electronic mechanism to read or write independently from each magnetic head so there are ten magnetic heads simultaneously ten reads or writes can happen you must appreciate why this is possible the electronic speed with which the bits and bytes can pass between the magnetic heads and the inside computer are tremendously fast as opposed to that the movement of the disk is so slow that even if I read all of these simultaneously I am not going to have any problem buffering that entire data pushing it in or collecting large amount of data from computer and separating it out so that's not a problem as we shall see so all that is simultaneously accessible what is not simultaneously doable is I cannot be reading from track 5 using this arm and I cannot be reading on track 7 using this arm if I am reading track 5 from this surface all arms are exactly position on track 5 only these arms don't move independent of each other there is a head assembly that arm assembly that entire set of arms move forward or back so that's the limitation and that's the reason why we form this concept of a cylinder otherwise the notion of a cylinder was not there is that clear any any question you can have anti-clockwise or clockwise but the way the it is designed is it rotates only in one direction you cannot try to imagine something moving at say thousand rpm and just because you are somewhere you say now rotate anti-clockwise how long will it take to stop that this rotation and restart it okay you are apparently not connected with mechanical engineering or you are good because if you were I would seriously doubt your degree there is there is an inertia physical inertia of movement and it is therefore see this when they rotate they don't stop they keep rotating perpetually whether you are reading or not because if you stop the time required to start is not as if you switch it on and immediately you can start reading you have to let that this speed stabilize and to stabilize that speed will require sometime at least one or two seconds and one or two seconds is a large time if every time you want to read or write you shut up the days and start again it could be extremely painful in terms of the speeds that you have the rest of the mechanism that's not all right. So that is the reason why this typically move only in one direction and all arms move like that for the simple reason that you want to amortize the cost of this motor which moves this arm forward and backward if you wanted each arm to move separately you could design that but when you were to provide a motor for each of the arm and it will not be cost effective. So all that is connected with costing that's all design wise by the way there have been attempts to answer this question more fairly there have been attempts where a single disc has been made with multiple arms so one arm here one arm here one arm there and those arms could be positioned separately so as the disc moves you could read from multiple tracks or you could say this arm will read only these sectors these arms will read only these sectors effectively increasing the speed of retrieval of data but in a commoditized world you generally standardize the complete manufacturing and operational process and that is how it is now sorry CDs are mostly single sided so the CD drive if you see it will have a single head it won't have two heads but there are double sided CDs available there are double sided DVDs available these are technical differences fundamentally it does not matter all that is either increasing capacity or increasing speed or both but ultimately the boundaries of movement will decide the speed with which you can access information and two things that you should remember always as the most important or paramount important thing for a day is are these two seek time and latency as long as you can do simple arithmetic with these two quantities you can know exactly whether this particular disk is useful for your purpose or not as simple as that yeah yes we don't ensure the the disk drive the processor under the command of operating system which controls the described system ensures all that so if necessary it will not read as fast as the physical desk drive may permit for example suppose you have connected 400 disk drives to a single computer 400 is possible now your 400 controllers but the computer's internal bus is not capable of handling that kind of thing then even though you may issue an instruction to read from all 400 days operating system internally will decide that it will first read from these 20 next from those 20 next from those 20 so you and I don't have to worry about if we were to worry at that level we will not be building information systems will all be computer technologies worrying about bits and bytes and reading the idea of the technology is to buffer the other usage from the technology relevant points what we are discussing here is just to understand how these technologies work but we are buffered by several layers which we shall see shortly yes so coming back again the excess time to information whether you want to read or whether you want to write two main components seek type the time to move the excess up okay how much time and latency or rotational delay latency the general term latency is perhaps the most important term in information processing because you have to worry about latency of moving information or accessing from but latency is used in the context of disk drives as rotational delay which is average half rotation is that very clear why average half rotation because you might have just passed that point or you might be just reaching that point so it is zero latency or one full rotational delay later and seek type of course time to move the access using these two simple things you can do very reasonable computations to find out whether your requirements are met or not met so here are some storage excess timings rotation a speed from a floppy disk 360 revolutions per minute so what is the time for one rotation it's not exactly 83.3 but I think it's 83.3333 something like how do you find that out 360 rotations per minute means in 60 seconds so 36 rotations in one second that is thousand seconds divided by 36 is that the correct number I think so in thousand seconds there will be six rotations no yeah six rotations so no how is that yeah sorry rotation is half half the rotational speed not one rotation but half rotation is the latest is that number correct can somebody cross check so is this correct like 83.3 milliseconds is that time required on an average to access to to wait for the rotation wherever you have recorded that information the average seek time is 4 milliseconds to 20 milliseconds 20 milliseconds in case of a floppy disk 4 millisecond in case of a hard disk the seek time may appear to be 5 times more which is okay but that is not the important thing for a hard desk the rotational speed is much faster earlier hard disk used to be 3600 rpm modern hard disk typically rotated 7200 rpm 7200 revolutions per minute by the way is very fast speed that should answer your question you know when you are rotating something at 7200 revolutions per minute you cannot you know stop it and move it the other way around you can actually compare it with have you played that top anytime Bhora Bhora Gumaya Bhora Gavi so you spin that Bhora rapidly and then it starts rotating now imagine having to stop it and turn the other way around the effort itself required will be too much so that's again coming back to saying why you keep rotating in one day in fact if a hard disk is at stand still just to start rotating will require a few seconds before it stabilizes at this speed that's why before that you generally hard disk in information systems are never stopped you will find some laptops you know which you are not using laptop for quite some time you are doing some simple heating on no disk access is made the disk will stop at that moment try to save your file because some sound will come the disk will start rotating and you take some time before it is saved while the disk is rotating you say save it gets saved very quick the difference is because of any so is this clear the fundamental difference between floppy and hard disk is that the floppy rotates only at 360 revolutions per minute hard disk rotates at 7200 revolutions per minute another difference the magnetic head which is meant for a floppy drive actually touches the floppy drive so it actually touches the floppy drive and reads and writes because it touches the friction the mechanical friction after some time you can have a completely one look that's why the floppy goes bad very quickly if you take the floppy out and remove that cover you can see the the practical hose we call it a see-through floppy and you can see through it is nothing very hard disk or magnetic head never ever touches the surface never ever now that means it's a it's a more difficult technology the head actually floats on top of the surface there's a few micron gap and so beautifully organized because at 70 to 100 if the head was to touch it the head will break or the surface will scratch so that's a different technology altogether in fact many times when you have a major disaster with that desk they call it head crash that means somewhere the mechanism did not work and one head actually bungled up and touch the desk and couple end of it so that that technology is different and it is because of that that it can rotate at this speed and read and write at that speed anyway coming back to our original problem of time to access information rotational speed which is latency means half the rotational speed and average seek time of 4 millisecond to 20 millisecond these are the two key parameters so let's try and solve a problem here I told you can do arithmetic simply you have a 1 gigabyte desk you you don't get 1 gigabyte disk very easily now you get 40 gigabyte desk so you can you can translate that appropriately let's imagine that that hard disk has 800 cylinders it rotates at 70 200 rpm and let's say the average seek time is 12 millisecond and you have floppy disk the capacity is 1.44 megabytes rotation 360 rpm the average seek time is 40 milliseconds these are the parameters given find the time required to backup a 512 megabyte sequential file on a floppy so imagine that 512 megabytes of a file has been written it's half the capacity of the desk okay so you can assume whichever way it is stored you can assume it is stored on the sequential cylinders of the disk so that easiest you can keep moving from a track to track and that's a sequential file and you have to store it on a floppy obviously 512 megabytes will not fit onto a single floppy because the floppy capacity is 1.44 megabytes require multiple floppy but how long will it take to backup a 512 megabyte sequential file on a floppy disk so you have 1 gigabyte desk and you are floppy as a backup you want to safeguard that if the disk crashes or something goes wrong your file is important let's say the file contains all your accounting transaction or medical history or important information as far as the disk is concerned it does not give a diameter as to what is the semantics of that information it has so many bytes it needs to be conducted so as information site is you have to work out a backup and restore scheme you know in case of a problem so if this is the problem so tell me how long will it take can you do some simple arithmetic I always claim that at least 50 percent of the major problems of the world can be solved by a simple arithmetic provided you put the parameters right I would like to know what is your answer how many seconds minutes hours it might take it's wonderful no more than 8 seconds you could have also said more than 0 second but 8 second is it is it realistic what perhaps more than 8 seconds for writing the entire file on a floppy okay very very interesting you are moving the floppy disk at 360 revolutions per minute first of all it is very obvious to you that writing on a floppy is going to be much slower than reading from a desk so the reading speed actually does not matter as long as it is much more than writing speed are you seriously suggesting that within 8 seconds I can write 356 floppy so then 8 seconds is not the correct timing I have to back up 512 megabytes of data so here is a solution first I analyze the given data I do look at my problem seriously so I do look at my disk cylinder capacities 1.2 gigabytes divided by 800 because there are 800 tracks and that means each track is one cylinder okay so at a time I can read one cylinder in one rotation wherever I have put that heads so the cylinder capacity is roughly 1.5 megabytes which I say roughly is a floppy capacity so that means this information can be copied or read in one rotation after a seek once I seek I can read this much of information from the disk it will take about 12 milliseconds average seek time and 4.16 milliseconds is the average rotation delay totally about 16.16 milliseconds that means the time it takes to read from a desk one floppy full of information is 16.16 milliseconds I need not even worry about that that's the purpose of showing this approximate calculations for backing up 512 megabyte 5 over 250 floppies would be needed that is the first observation because the capacity is 1.44 megabytes time required to write on floppy how much is that time rotation takes 166.6 milliseconds seek time is 40 milliseconds so one track is written in 200 milliseconds remember I am not right reading I am writing so one full rotation means I can write one track after writing one track I go to the next track then next track then next track etc. so one track is written in 200 milliseconds how many tracks you assume that the original problem did not specify if you are allowed you would immediately ask me how many tracks because without it you cannot find out how long it will take suppose I told you entirely one track contains 1.44 megabytes then your entire solution is 200 milliseconds but if there are 80 tracks how much does that become time to write on one floppy is 80 into 200 milliseconds please note that this has nothing to do with the speed with which the information can be handled inside the main memory this is the time physically required for the stupid floppy to write and it is not 1.5 4 MB which can come in one shot and get written remember while the disk is a direct access device at one time I can write only on one track only when the track is fully written then I can go to the next track then next track there are 80 tracks so that means it will take 16 seconds to just write on one floppy not even 8 seconds 16 seconds you took half the revolution for us but you are writing one full rotation you have to write 16 seconds is the time to write one floppy now you have written that floppy what you have to do now that let's say the backup program tells you floppy is written you have to take that floppy out put a some kind of a label on it insert a new floppy inside is that a trivial job once we insert a floppy the operating system has to recognize that a new floppy has been put in is that a trivial activity those of you who recognize that assume that it takes two to four seconds time for taking a floppy out labeling and for entry in a record long why just labeling is not sufficient you must maintain a manual register in itself floppy number one twenty three four twenty four one twenty five whatever whatever some info assume that it is ten seconds okay because he's human type you can say no no no I'm very efficient so much second okay much second but some some time non-trivial non-zero time what does it add up to 16 seconds plus this time you know I got a very clever answer to batches ago he said so the moment that program says that thing is over I'll keep the other floppy radio take it out and put it in and then why it is writing I will put labeling etc etc clever answer so you take it out and put it in but still operating system has to recognize that you have to take it out put it somewhere so maybe two seconds so don't take ten seconds but two seconds at least two seconds plus sixteen seconds ordinary mortals like me will take ten seconds so sixteen plus ten seconds is that time per flop how much does it amount to close to three hours with half a minute per floppy 350 floppies will need 175 minutes or close to three hours this is if the operation is continuous what if one floppy gets wrongly labeled now imagine the human errors or machine technology one floppy goes by while recording what do you do typically you will not even come to know that recording has gone bad unless you try to read it you know when you do these kind of backups that is the reason why backup programs don't just write they really don't confirm that what has been written is exactly what I wanted to write if you wanted to do that double the time ultimately pay the risk so what if a floppy does not read later in short what is the correct answer to this problem the correct answer to this problem is it is wrong to use floppy is a backup for large files from an information perspective information system perspective that is the correct answer it's not the arithmetic but the arithmetic is so skewed that we should immediately so now we should still do all these computations are my but somebody says now I am giving you a computer system with one gigabyte of disk and a floppy drive for backup say thank you very much not good enough if my disk capacity is one gigabyte and now I have what 40 gigabytes 80 gigabytes 100 gigabytes that is why people do not give you floppy drives anymore they give you what CD rewritable CDs now writeable DVDs so what is the capacity of air you can now map the same problem the scales are different imagine your 150 gigabyte disk and 760 megabyte CD run and you have a writeable CD and people who have sold you that machine would have convinced you the CD can be used for backup now imagine that you have a 100 gigabyte file which you want to back up on CDs 120 CDs to be written each CD after writing you have to read to confirm that it can be read fortunately CDs are more reliable than floppies but still there are CDs and you have to label each CD so is that a correct backup strategy it is not just remember that these ratios are very very important when you talk about backup devices and things like although the example is centered around the backup timing and so on the fundamental fact of life is that capacities of the total disk drive the latency and seek time are the cardinal things by which you can decide how long it takes to access information let's go ahead and concentrate only now on reading and writing information meaningfully for our purposes okay so for backup and restore operation you need special solutions which exist and you can permit incremental backup so you will very rarely put a half gigabyte file as a single file half gigabyte file does not fall from the sky in the first place okay if it's a some kind of a master file where you are adding let's say file of records of alumni now the alumni all 33,000 of them did not fall from sky overnight they have been accumulated every year we are 300 or 350 so I will consequently I can keep backing them up every year as the backup increases that's called an incremental backup just an example but that's the kind of backup strategy in the context of information systems that you would like to derive however the real advantage of the desk is not for just storing the information and dumping it in the backup the real advantage is the ability to access it very quickly and that is why we like the notion that directly accessing data on desk is very important here's a thumb rule at 7200 rpm you can per second the number of input output operations that you can conduct on a desk are about 50 blocks we are not defined what a block is okay a block is some storage imagine the context of the diagram that I drew consider a sector as a block so a sector is a portion okay now imagine that in actual practice on the desk the information that you seek to read or write is not organized beautifully in the same cylinder within the same sector etc some information is written here some information is written there some information is written somewhere else consequently to access any piece of information which for the time being we call a block in order to access a block on the desk and how to randomly move my arm somewhere and wait for some half rotation so this is called a random IO now how many random IO's can I do per second I have said here 50 50 blocks per second can you justify this 50 blocks per second in one second if I can access 50 blocks then what is the time required to access one block one second divided by 50 that is thousand millisecond divided by 50 which is how much 20 milliseconds you will realize that the average access time and the average rotational delay together could be about 20 milliseconds for some slower this it has improved significantly now imagine that 20 millisecond has become 10 milliseconds you can make it faster than 10 because there is a rotational delay that is the killer the excess time is not much for hard desk but rotational delay if you want to randomly search somewhere that rotational delay is there so instead of 50 now you can say that the excess is about 100 blocks per second what we can do now is very important if we imagine that on a hard desk of a fairly large capacity the information that is relevant to us whether it is account information whether it is academic information of a student whether it is census information whether the insurance policy information these information pieces are stored in blocks and I want to randomly access a block and I imagine that my information is spread across the disk then ordinarily how many blocks can I access per second is about 100 50 to 100 and in past 30 years the number of blocks that can be accessed has actually moved from 25 to 100 that's all electronics on the other hand has moved far more rapidly so consequently the memory speeds are extraordinarily faster as compared to this is about random access now given 100 excesses 100 blocks per second how long would it take to access one required record suppose I want to read let's say one student's record CPI that record is how much the real number name CPI hostel number take our schema 80 hundred by record obviously if I know the block on the desk in which that students record is there the time that I will require a random excess is time to read one block which could be one by 50 seconds or one by 100 seconds provided I know which block how many blocks can be there what is the notion of a block that's an important what should I say component of the direct access a block is typically defined as a fixed capacity size described by the operating system not by the disk I will recommend that you read the Unix file system as a very interesting mechanism of indexing it actually formats the disk puts aside several blocks just to keep information about files and then maintains a list of free blocks which are available then whenever you ask for storage it allocates those blocks you might edit a file and delete some portion in which case you really some blocks so block number 23 released by you then the Unix operating system will allocate block number 23 to someone else who asked for that additional block later so I might have a file which is recorded let's say in block number thousand one thousand two thousand three and then 23 because 23 became the available block so consequently there is no guarantee that my information will be necessarily written in sequentially contiguous blocks why is that important because sequentially contiguous blocks at least originally when the disk was formatted actually where on contiguous tracks or contiguous cylinders consequently reading or writing would have been a bit faster so I had assumed that by reading or writing any block will take about 100 for a second consequently I must minimize the number of blocks that I read for any information handling is that is that clear imagine now if I have the data for all the library books in a disk remember like the index that we mentioned we are trying to find out on a computer I want to search a particular library book with its title these that and the rack position and I have the name of the library book or something and I have stored all of these data on the disk so how will I do that search quickly so for that I have constructed an example here here is an example of index schemes on the disk assume that there are records okay records which I have stored if I have records like a CPI records or employee records or what suppose each record has a pointer or address like in a position in a array so can we not prepare an index let's say there is a key of that record let's say the key is a 23 p 4 1 5 6 9 7 this is a this is the attribute that we know let's say part number is a part number the part numbers record is stored in some block and let's say this is the pointer to that block and let's say this is a 8 digit number 8 digit number means a lot of blocks I can have truly modern this have those many blocks supposing for each key that I have I prepare an index table like this then will it not be easier for me I search this index and in this index I get a pointer then I go to that pointer to go to that pointer I will require one block access right to actually once I get the pointer but how do I get a pointer because I don't know that your record is block 127 somebody versus record is block 1000 something how will I know so you him how I will identify some key which is very number in your case in this case this is the key so suppose I make like this what will it mean where do we store this index suppose we store this index as a file on the disk okay we store this index itself as a file on the disk how many blocks will the file occupy depends on the size of the file see imagine I am putting together a database of all the students appearing for 12 standard in let us say southern states easily about 1.28 crore records how many blocks will an index of 1.28 records occupy imagine the block size to be 512 bytes that is one block size let's go back here the key is 24 bytes pointer is 8 bytes totally 32 bytes one entry of indexes 32 bytes how many entries I can put in a block 128 entries assume there are 100 1.28 crore records deliberately chosen this number then I will have 1 lakh blocks just for the index so the assumption that I will quickly look at the index and then go to that block the time required to go to that block is 1 by 100 seconds or 1 by 50 seconds but to search that block number I will know how to read each one of these 1 lakh records 1 lakh blocks how many seconds assuming 100 blocks per second I have to read 1 lakh blocks on an average half lack because I might find it somewhere half it can I do binary search I can't because I don't know where these blocks are written okay so average time required to search the index if scanned sequentially is assuming 50 blocks per second read about 17 minutes after 17 minutes I will get a block which contain that fellow's information I say ah now within 1 by 50 a second I get your information is that good not useful so you see the non-trivial problem that we are talking about indexing something occurs to us very quickly but indexing on the days when each block if read or written randomly will require 1 by 50 seconds or 1 by 100 seconds we think it is very small a time but if the index itself has 1 lakh entries how will you handle that