All right, welcome back. Good morning, everybody. Good morning. This is like the largest class I've had for a while. I think I should hand back exams every day. So I hope you guys had a great break. As you can tell, today we're kind of off to like a slow, relaxed sort of back falling into non-spring break. So I hope you guys had some good time off. And I didn't ruin it by handing back an exam today. But today the goal is to go over the exam. I'm going to put up the stats, give you some idea of how you did relative to the rest of the class. The average on the exam was pretty low, it was about 25. So maybe that makes you feel better about your score or really good about your score, depending on how well you did. So and then I want to go through the exam sort of question by question just to give you a little bit of an insight into why these questions were on the exam, what they were designed to elucidate about your understanding. So the point is that the first time I'd ever written given an exam, and I don't like it. And you guys are probably thinking, well, if you don't like it, then stop. But the point of doing this is not to create a hierarchy within the class. The point of doing this is so that you guys understand the progress that you're making towards learning the material that we'd like you to know. The nice thing is that on some level, the rest of the material that we're going to cover for this semester kind of starts to feel like variations on the same theme. We're going to see a lot of the same design principles that you were asked to write about in one of the long questions occur over and over again. And on some level, when we talk about storage and virtualization, we're going to see some of the same ideas emerge. So I want you guys to feel, if you didn't do as well as you wanted to on the exam, that we're going to continue to reinforce some of these concepts. I would rather have you guys remember one or two things from this class. If I have to have you guys repeat them every day, and I have to find eight different ways to kind of get out them and get you guys to think about them, then cover all sorts of material and have you guys not remember anything except that the class was hard and the instructor wrote these really terrible exams that were really difficult and things like that. So we're going to continue to kind of drum in some of the basics here. But let me talk a little about the exam. I'll also talk a little bit about how grading in this class works, because I think it's kind of an appropriate moment to discuss that. All right. So the midterm, and this is not working because it's not on, that's a good reason for it not to work. OK. All right. So just a couple of announcements before we get going. We're going to have feedback on your design documents out by tomorrow. The TAs don't know this, but they're going to be working hard on this for the next 24 hours. Well, also today I think post some idea of the rubric for our grading of the design documents, meaning here are the things that we wanted you guys to cover. Here are the things that we hoped you unearthed. Here are the things that we think are hard about the assignment. You guys may find that there are different things. But hopefully by this point you're also well into the process of making some significant progress on assignment two, which is due a week from today. And then again, so for the rest of the semester we're essentially at the halfway point. And we have about six weeks to go. We're going to spend those six weeks discussing largely storage and virtualization. I'm still unsure about how I'm going to do storage partly because I feel a little bit weird talking about spinning disks because I think by the time you guys are mature sort of Jedi masters, spinning disks won't matter anymore. Or it will be very rare for you guys to actually encounter one. So we'll figure out how to do that. And then we're going to talk about virtualization. And we'll also sneak into a couple of lectures about operate system structure, which is usually covered earlier. But I decided to kind of wait because I think it makes more sense to talk operate system structure once you've seen the structure of an operate system. So let's you know what the components are. We can talk a little bit more about the design and talk about micro kernels and macro kernels and monolithic kernels and exo kernels and multi kernels, et cetera, et cetera. So this gets to be a little bit alphabet soupish, but it's kind of fun. All right. So again, this is my goal today. If you have questions about your specific grade on one of the questions, please approach the core staff during office hours. The grading for the exam was done over break while you guys were out partying and then soaking up some sun. And it was done by Feng, who graded the short answer questions. And Anodipa, who is proctoring an alternate midterm makeup exam today, but she graded the multiple choice and the long answer question. So just so you know who to blame. But if you have specific questions about the exam, please talk to them or talk to me if there are issues. Finally, I just want to point this out just to head off any problems, which is that we scanned all the exams. So if you think that you could add a little bit to your answers and then turn them in for regrading, don't try it, because they're all scanned in. And why not? I mean, we just did it because it's easy, right? And you could just scan things. OK, so remember, going back to our grading overview, this exam was worth 12% of the points in this class. 4% you got for free by just taking the preterm exam. And then 12 percentage points for this, the final exam is going to be worth 24 points. The final exam is probably going to look a lot like this, actually. I decided when I wrote this exam, I kind of like writing exams like this. Maybe you guys don't. But I think I'd rather write an exam like this than a long multiple choice exam. There's a possibility that the final will be a take-home exam as well. I'm still sort of thinking about it. How many people would enjoy doing a 24-hour take-home final exam rather than coming to class for whatever it is, like an hour, three-hour winter take-all? Who would prefer to do a 24-hour take-home exam? The 24-hour take-home exam would be written and designed to take like three or four hours. It would not be designed to take 24 hours. It's not a 24-hour long exam. It's an exam that you can take within a 24-hour window of time. Let me see those hands again. People who prefer a 24-hour take-home exam. People who would prefer to sit for a whatever it is in two-hour exam. OK, so that's about 50-50. I think I get to make up my mind about this, which is good, because that's what I was going to do anyway. OK, well, we'll think about how to do that. All right, so this is just a reminder about how this works in case, again, you're disappointed by the midterm or related by the midterm.  So here were the statistics for the midterm. Again, the average was pretty low. The average was about 26. The median was also about a 26. We had 89 people who took the primary version of this exam. Most of you guys are here. If you took the alternate version, you know that. If you took the primary version. If you don't know what version you took, then you took the primary version. I wrote several versions of the exam because I gave them one early. And again, I don't want to blow us out of proportion, but there were some people here who did very well in the exam. So it was actually kind of interesting that the max that most people got in the exam was about 40. 40 to 42. That was where most of the high grades. However, there was one person who I think who maybe or not maybe here who got a 48 out of. So is Robbie here? Nice job. So the following top five grades, Keith, who I know is here, 43, nice work. John Gerber, 42. Where's John? He's going to be embarrassed a little bit. Jimmy Woo. Now everyone's going to come to you guys for questions. That's why I'm doing this. Is Jimmy here? I don't think Jimmy is here. And then there was a group down at 40. So Michael, Vikas, and John Longenacker is here. Michael's here. Vikas is also here. And Jason, I know, is out. So let's give these guys a little hand. They did well on the exam. And again, I mean, the only reason to do this is so you guys can bother these guys when you have questions about the material. There's one of me, there's six of them, seven of them, eight of them. I should have given more high grades. Eight of them. So if you're struggling, these are good people to talk to. They understand the conceptual material. How they do on the program and assignments is a totally separate story. But these guys are getting the concepts that they're good people to talk to. So let's go question by question. So a multiple choice were designed to be easy. How many people felt the multiple choice were pretty easy? I hope they were. I mean, the multiple choice were exactly taken from the slide. Literally, like I said, I looked at the slides and I said, here's a multiple choice question. Here's a slide that has three things that are policy and three things that are mechanism. I can turn that into a multiple choice question. Actually, I turned that into two multiple choice questions. There was a parallel question on the alternative exam. So the point is that these were not designed to be hard and by and large, people did well. The median out of 10 was an eight. The average was a seven point again. We didn't break this down question by question. I'm curious how many people got the coming to class on time question, but I don't really care. So maybe we'll try to figure that out. All right, so the short answer. So let me explain this. So the short answer what I did is we computed. Let me go back a second. So they're 89 total. And we computed how many people decided to answer this question, which means they filled out something in the blank. And then we also tabulated for how many people was that question one of the top four short answer questions. So some people answered more short answer questions than they needed to. And for those people, one of the answers wasn't counted. So you can see that it was clear to me in retrospect that some of these questions were easier than others. So for example, question four was a very popular question and for good reason. That was the question on interrupts. Yeah, apparently that was easy. Because almost everybody decided to answer that question and the average was 3.8 out of 5, which is by far the highest. On the other hand, question six, so you guys were pretty good at identifying the questions that were difficult. Not perfect though, because 84 people decided to try to answer question seven, which apparently was harder than you thought it was. So these are just summary statistics. I'll post the stuff on the website, but let's give some idea of the overall breakdown. As with any exam, my goal was to write six questions of equivalent difficulty, and I failed. Some of these were easier than others, or maybe I just did a better job teaching some of this material. So the point is that there was some spread in the average here. So for the long answer, the overall average, so as far as I could tell, the long answer question is really where people struggled. The average on this question was below 10 out of 20. So I think most people, this dragged down a lot of people. People lost a lot of points here. And I understand that, because this is not something that we've done a lot of in this class. This question asked you guys, not just to repeat or to remember material that we've covered, but actually to try to synthesize some new thought based on existing concepts. On the other hand, again, for this particular question, the two alternatives showed a fairly large grade spread. So the alternative one, we'll go over each one of these answer by answer. Alternative one was the user versus kernel multi-threading question. People, about half the people who took the exam tried that question and about the average was quite a bit lower. Alternative two was the design principles question. So the average on that one was a little bit higher. Again, if you have questions about your specific grade, please come talk to us. OK, any questions about the breakdown here? Questions, doubts? This is kind of supposed to be a little bit of a struggle session for me. So if you guys are mad about the midterm, it's a good time to say something, to be like, and this is ridiculous. I answered alternative one and I got totally screwed because it was hard. No one feels that way. I'm sure people feel that way. Everyone who answered question one feels that way, D. So I think alternate two was an easier question. And what can I say? I mean, I feel like that's just, alternate one was designed to be a little bit more technical in nature. I think it was a fair question in that, if you understood the material that we presented in class about threads, then that should have been an easy question to answer. But let me be honest. Alternate two, so alternate one was kind of a question that was aimed at the people in this class who might really think that they will go out and do sort of serious system programming some day. Alternate two was aimed at the other 90% of you who are taking this class because it's a requirement and don't intend to ever hack on a kernel again once you get through this miserable OS 161 stuff. But you guys are going to write software. And as we talked about in the beginning of this course, one of the things about this class is learning design principles that you can take with you when you work on other software projects. So that's what alternative two was really trying to get at, was design principles that are broader and bigger than just computer systems. They're not about just operating systems. They're not about just computer systems. They're bigger and they're good ideas that you can take with you no matter what you're working on. And really in some ways, the question was also trying to push you guys to take some of these good system design principles and find kind of cute applications for them outside of computer science. I don't know how many people answered. One of those, at least one of those examples was something that wasn't drawn from computer systems. Did anyone come up with good? OK, John. Did anyone come up with good examples that weren't computer systems? How many people came up with good examples that weren't from operating systems, like networks or other types of programming? OK, so that was kind of the point. Many other questions. We're looking at the score by score breakdown. All right, so let me step back. And in case you guys are nervous, because this exam, and I told my wife and she was like, oh, man, that's terrible. People got a 50% in here exam.  Yeah, I know that. Nothing different than what she tells me on a regular basis. So the point is putting these grades in context. So this is how we are going to grade this class. This is actually how it's going to happen. So at the end of the day, you guys are essentially accumulating points. So these are the first points that you've accumulated that we've actually measured. We're almost done with grading the assignment zero. We know we're behind on the assignment grading, so we need to catch up on that. But we're going to add up all your points, and then we're going to put you guys up on some sort of big board, and we're going to go through them. We're going to start to look for logical clumps of students, students that we think their performance overall, when we've calculated all the different components, is indistinguishable. And normally what happens when you do this is that you see that there are cohorts, right? That there's a group of students that are all at the top within a certain range of scores, and then there's kind of a natural place for a division, right? So this is a very much a manual process, and the point is to try to map these points that we're giving you to letter grades, but that's not actually going to happen until the very, very, very end of class, right? So a 25 out of 50 on this midterm is meaningful only in the sense that there's 25 points that might put somebody else, although there was almost no one who, I mean nobody got a perfect score, and there were very few who got over a 40, right? But that might put them into another cohort at the end of the day, but it probably won't, right? Because a lot of the points are still on the board, right? So most of the points are for things like the programming assignments. The other thing I want to point out about the midterm in case it's not immediately obvious is that the midterm tests your ability to come in here and sit down for 50 minutes and really nail an exam based on the material you have in your head, right? And for people like me, I'm not super fond of that skill. That skill has uses, right? But the number of times that you guys are actually going to sit down and have to, there's 50 minutes and there's a bomb about to go off, and if you don't answer the question correctly about user versus kernel multi-threads, the world is going to perish, right? This is not a feasible scenario, right? It is possible that you'll have a month-long deadline and you'll be trying to push into a piece of software and you'll be really required to pound out some pretty good code, but that's really more about determination. So I see this part of the class, this component of your grade, the midterm and the final, really. So that's about 40% are the, this is the brightness component, right? This is the smartness component.  The other 60%, which is thankfully bigger, is the determination points, right? So you guys don't have to stop working on these assignments till you're done, right? Or until you run out of time. And when you guys turn in assignment two, there might be one group that spends five hours on it. How many people have already spent over five hours on it? Okay, so there probably won't be a group that says five hours on it, but maybe it'll be the group that spends like 15 hours on it, right? And there's gonna be another group that spends 150 hours on it. And we can't tell it apart, right? All we're gonna do is test it and see if it works, right? So that part of the grade is really much, much more in your control. I know you guys have other things to do, but that part of the grade is kind of like being able to take the midterm and spend twice as long or three times as long as somebody else on it, right? It's not over until you give up, okay? Any questions about the grading for overall class? And I think, I'm on a slide, so okay. So let me pull up the solution set for the midterm, which I will make available via email today. Okay. Come on. And okay, so I'm not gonna dwell on the multiple choice. Does anyone have any questions on the multiple choice questions? Questions that they think are, answers they think were just blatantly wrong. Okay, going once, going twice, questions on the multiple choice. All right, good. All right, so let's talk, let's talk, let me go back here and just review, okay. So why don't we go through these questions in some sort of reasonable order. So the most difficult question based on the average as far as the short answer was question number six. So let's look at that one. All right. All right, so this was a question about kernel privilege. All right? The reason this question is on the exam is because kernel privilege is the thing that makes kernel, the kernel different than just some normal application, right? The kernel is a piece of computer code, right? I think some of you guys are starting to get a feeling for this. Let me see if I make this a little bit bigger. As you work on assignment too, right? But the kernel is a piece of computer code. And it's in some ways very similar to any other application you run on your system, right? The difference is, as we've talked over and over about is that the kernel has special privileges, right? The kernel has special powers that other applications don't have, and it's required to do that in order to multiplex resources, right? So this question starts with the premise that these privileges are needed to multiplex virtual memory and then ask you guys to describe what special privileges are required, how they're used, and what would happen if the kernel didn't have them, right? So I didn't get a chance to see the individual answers. Does anyone who answered this question want to make a comment about their answer or where they got hung up or why this question felt difficult? One of the things I worried about with this question was just that maybe it was even a little too obvious, right? Like the last part, what would happen if the kernel didn't have these special privileges? Well, applications could just sort of barf all over each other's memory, right? But maybe we've got you guys to the point where you don't even see that as a possibility. That's just the world can't be there, right? Any questions about this question on the exam? Who answered this question? Raise your hand. All right, do you guys don't have any questions about this question? All right, let's go on. Okay, question. The next most difficult question was question seven. Describe the trade-offs surrounding memory page size. What happens to become pages become very small? What happens to become pages become very large? So I'll be honest. I didn't anticipate this question was going to be hard. How many people answered this question? Raise your hand if you answered this question. Okay, this was a popular question to answer. Does anyone want to make a comment about their answer and how they lost points? Or whether they lost points? Isaac? Nobody said that you had to mention blue and black trade-off exactly what you're saying. It's what you wanted to say. Okay. It's not even exactly what they're more to answer than that. Well, I mean, again, I felt like this question had a pretty straightforward and short answer. So maybe the grading on this question was a little bit aggressive. It's possible. So you got what? I got three out of five. Okay, and can you identify things that were missing from your answer? I didn't do good stuff as far as I would have asked you. Ah, okay. Maybe bad, bad, bad things. Gotcha. And there is a fair amount of symmetry to these things. Like the good and bad things are paired. So maybe we will revisit the grading of this question in terms of, on the other hand, of course, you have to remember, as long as the grading is consistent. Although you're right. I mean, we should make sure that we rectify this with respect to the other questions. John? Okay. Keith? Okay, okay. So maybe for this question, we need to go back and take out some of the symmetry. Can we do that, Feng? Okay, so if you answer this question, right, this is why we're doing this. If you answer this question, and you lost points, and again, I think I was, this is the question that I was most confused about because a lot of people chose to answer the question, which means I think that people sense that this question was an easy mark, right? And yet the grading was a little bit low. So it sounds like maybe people are missing one or two points on this question. If, I guess there's, let's see here, I guess there's two things we can do here, right? And I'll consider both. The first one is easier. The first one is just, we apply some sort of across the board correction to this question only, right? Maybe we add a point, right? Or two points to everybody's answer. The other approach is, you guys come in individually and meet with the core staff and we try to figure out how your answer makes sense, all right? So we will think about this. I don't wanna open up massive cans of worms here because if I start doing this, then the people who answered question six are gonna wanna go back and start complaining about question six, right? But I think that's a fair point. I think that there is a lot of symmetry to this answer. So maybe what we can do is make sure that if people gotten the bad points on both sides or the good points on both sides that those reflect across, all right? All right, okay, so let me, somebody other than me is listening so we can make notes of this. Okay, so let's go on, that's a good point. So the next most difficult question was question two. That is, ah, no, that's this one. That was easy. Question two, okay, so this is, this I was also a little bit surprised by because I thought this question was mechanical and probably not that difficult to go through. So this was not a terribly, this was the least popular question to answer, okay? Is anybody who did this question and is feeling unsatisfied by their grade they received wanna make a comment about the question?  And I even made it easier by using base 10 arithmetic, which makes me feel a little dirty, but I think it's the right thing to do, wait. Physical page number 120. Well, I mean, we wanna see the whole address, right? We definitely wanted to see the eventual instruction that would have been executed. I mean, if you think you have an answer that's functionally equivalent to this, then come talk to us and we'll look at it again. Anybody else comments on this question? Yeah? Yeah, I mean, for C and Y, we identified whether there'd be a DLP point or a page point and are we really moving on that? Okay. So we're very lost. Okay, I mean, maybe we can, we might think about making that one, but yeah, I mean, we wanted, we wanted to know kind of what would happen, right? I think that was, I think that was specified, right? Describe what would happen of each of the following two of the instruction words were executed, right? And we went over something like this in class, right, with the segmentation. So I think I established some problems with this. Any other questions on this question? All right, now the next two, I hope we'll go a little faster because they were easier. So questions three and five were, both had pretty high averages. I think people did well on these questions. Question three, where's my, question three was locating bugs. And of course, there was no, there was no surfeit of problems with this code. Most of them were pretty obvious. And then question five was identifying between interactive and non-interactive threats. Any questions on these two, these two questions? Question three, question five from the short answers section. Any frustrations? I know you guys are just seeing the exam. We're just doing this right now because I want some feedback on the questions and I think we've already got some useful feedback. This is kind of the process of debugging the midterm. If you guys have doubts later about your answers, please come talk to the course staff, right? I mean, you guys, I'm sure you'll sit down and look at the feedback that's the TFs have provided, John. Yeah, yeah. So why don't, why don't we do this? I will have, I will have Fung and Anodipa try to come up with some, because I know they have rubrics that they used. So I'll have them sort of describe the rubrics and we can put that either on the solution side or we'll send it out via email. That's, that's a good point. In those cases, that's not, they're not always going to add up, right? Like there might be, if there's three parts and it's a five point question, it might be two points per part up to five points or two points off per part down to zero points, right? So, all right, any, any questions on three and five? And then the question that, that everybody seemed to really enjoy answering was this one, and I don't want to spend too much time on it because the medium was a four. So most people seem to do well on this particular question. Any questions, any questions on four? All right, going once, going twice, questions three, four and five. This is the soft underbelly of the, of the short answer question section. All right, so let's look at the long answer questions. Just don't have a huge amount of time, but we have a few minutes. All right, so I already touched a little bit on both of these questions, but let me give you an idea of rationale here. I'm happy to do rationale for the other questions. I know I kind of stopped doing that, but I hope the rationale, at least in certain places, is clear, right? So again, the system design principles is on here because these are the things I actually care about you guys learning or at least remembering, right? I mean, some idea of the existence of and the application of because I think that this, these are things that'll make you guys stronger programmers and stronger technologists, right? I mean, these are some of the hard earned lessons that the computer science systems community has spent 50 years, 60 years, fighting their way to understand, right? And the reason we try to teach people these is because not because they're not obvious, right? Because some of them are kind of obvious and that's fine. The reason that we teach them is because people, including me, smart people constantly ignore them, right? That's the weird thing.  It's like, well, why don't they do it, right? If everybody knows it.  I mean, this is a very, this is actually kind of a deep idea, right? For a lot of people and yet the number of systems that seem to struggle with this is pretty incredible, right? So my favorite example of keep it simple, stupid, do you guys remember Friendster? How many people ever used Friendster? Friendster, really, nobody? I'm old, okay. Friendster was an early social networking site. You know, how many people think that Facebook was the first social networking site ever created? That's good because it wasn't clearly. There were predecessors and Friendster was one of them, right? And it's an interesting, I mean, you can have a long conversation about why Facebook rose to the position of relative dominance in this area. But one of the things that Friendster tried to do was Friendster was entirely, Friendster didn't have any notion of school or any notion of company. It was entirely trying to connect people based on their social networking graphs, right? So the idea was, you know, if I'm within four degrees of separation from Isaac through our mutual friends, then I should be able to access information about it, so how often do you think that friend graph changes? It's like constantly, right? So, I mean, Friendster had a lot of issues, right? It was a really slow site, but I remember reading somewhere that one of their design issues was simply that they were trying to do all this based on these graph traversals, and yet this graph was constantly changing, right? As people were adding and removing friends, and so the system got so slow, right? And rather than think about a simpler way to address their problem that might not have had that feature, I mean, when Facebook came out, you could only, Facebook had these very, very nice, vertically oriented, you know, spheres of social contact. If you went to school with somebody, you could see their profile. That's how it was in the early days before they added 10 gazillion privacy features, right? But it used to be, you know, like if you went to Harvard and this other guy went to Harvard, you could see his profile, and that was really easy, right? You can imagine that makes determining whether or not you can see a person's information very, very fast, whereas for friends here it was incredibly slow, right? And now that Facebook has matured, it has some of those friends who are like features, right? But on some level, Facebook took a simpler, easier approach first, and they got it to work. They also had a site that looked better, right? But you didn't go to Facebook and sit there for 10 seconds waiting for the page to load, right? So it had some nice problems. Anyway, sorry about the digression, but the point of this question was to try to get you guys to talk about some of these design principles, right? Any questions about the second alternative system design principles question? And then why don't I quickly just, I mean, again, we're gonna send out these answers via email, but so examples of system design principles, separation of policy from mechanism. I think we've talked about that one multiple times. Keep it simple.  Use the past to predict the future. I think that hopefully that one's been drummed pretty well into your heads by now. Using caches to make a big thing seem faster or putting a fast thing, or using a big slow thing to make a small fast thing seem bigger. It's kind of the duals of each other, right? Adding a level of indirection to allow the system to have more control over translation and to play some games about where things are, and then avoiding doing things immediately that you might never have to do, right? So we talked about that with demand paging. Any questions about these principles? And then the other, again, I mean the other question here was the one about user and kernel threads. And the idea behind this question was to try to see if people had a really detailed knowledge of what it means to do threading. And I think this is a fair question because we talked about it in class. And also you guys are doing this for assignment two, right? So for assignment two, if you're off to the right start, you've seen a lot of the functions in OS 161 that create and manipulate threads, right? And there's no magic here, right? I mean thread state is stored in memory somewhere, right? Thread context is stored in memory and switching threads means unloading and reloading registers. And there's no reason that a lot of this stuff can't be done in user space and in fact it frequently is, right? As far as the trade-offs, right? I mean that probably is a part of the question that people struggled a little bit more with, right? And the fundamental thing you had to notice there was that creating threads and manipulating threads and the kernel requires context switching into the kernel. And we've talked several times about context switch overhead, right? And so that means that things like thread creation and thread destruction are very slow, right? So the general, and I'll let you guys again see the solution at some point. These are more difficult to view here because they span multiple pages. But the idea with this problem was that we wanted you to identify the fact that context switching is slow. That means certain types of thread operations are much more expensive to do inside the kernel. And that means that applications that use threads for sort of small tasks like I fork off a thread to handle the fact that the user clicked a button and then that thread dies or exits, those applications do much better with user thread libraries, right? Applications that use kernel threads like web servers frequently fork off a whole pool of threads that essentially sit there processing tasks from a queue and live until the entire application shuts down, right? And that's how they avoid the overhead of creating and destroying threads. They keep a set of threads around that is designed to be large enough for a large task that they might have to perform. But when the system is idle, those threads still sit there, right, and they're just sleeping, not doing much, right? Okay, any questions about the long answer questions? All right, so Wednesday, we're gonna go on. There might be a little sort of memory stuff that we need to clean up, but probably not, we're probably gonna do storage. So this is the third big unit in the class. We're gonna talk about disks, file systems. There's a lot of similarities here between virtual memory management. So we'll have a chance to reinforce some of that and that'll be awesome, so I will see you then.


Biofouling of submerged ship surfaces can have a significant impact on vessel operations, as well as the environment. In order to reduce this risk, proactive in-water cleaning, IWC, of biofilms from submerged ship surfaces has been proposed as a possible solution. However, this approach must be carefully considered due to the potential for increased biosecurity risks associated with the release of diverse microbes from ship surfaces. This article was authored by Eugene Georgiatis, Chris Cianni, and Mario Entombore.


ah, I already did that one I already did that one Land Oh high school musical. I forgot about high school musical. Oh good god Which one is this one? Hold on Tangled I see the light that was requested earlier. Mark's arm though Tails all this time. Yeah Strong music I'd love high school musical Hold on. I don't know which one breaking free Yes, yes, yes Yes, hold on. I don't know if we don't have any other doze though. So hold on If this if there's no more doze, this is it for the night All right, cool. We're doing one more send off song and that's it stream is over You guys can leave the stream because we're doing high school musical High school breaking free breaking free high school musical. Love this. I actually own the extended dvd version of the First high school musical the second the third weren't as good. The first was amazing. I love it. Zach Efron, baby Dude, dude, Zach Efron. I will give you Vanessa Hodges. Oh, Vanessa Hodges is great But I don't care about the hotness dude. Zach Efron's cool, man Yeah, I know I don't know how he went from this where everyone thought he was lame to like Baywatch and everyone thinking He's hilarious and awesome. Yeah. Oh, no, it wasn't wasn't Baywatch. I did it. I think it was neighbors Yeah, definitely neighbors like he was really good neighbors. Yeah, definitely I'm sorry.  Well, what a surprise.  It's what I mean. Don't forget Ashley Tisdale, too Ashley Tisdale Well, what was cool when I liked about high school musical and this is we was a disney thing But what I liked about is one it was like the return of musicals back then and two They can actually sing like they sing their own parts All in this together Oh, wait, that's all right. We're singing. Oh, yeah, you know what fine fine Collin you're gonna get your wish too. We'll end with that That's the same song. I love that too much I love me. Here we go though. I love in the new one. I love me some David Tennant Obviously, I'm doing the guy part because I chose the song. Well, I you know, I don't even know if I know this song But you know, it's okay. The guy starts out The guy starts out With soaring Flying There's not a star in heaven that we can't reach We're trying So we're breaking free. Oh, good god You know the world can see us In a way that's different than who we are Creating space between us To separate us But your faith it gives me strength. I think that's spotless strength to believe We're breaking free sorry There's not a star in heaven that we can't reach If we're trying You're breaking free. Oh, I'm breaking free Can you feel it building? Like a wave the ocean just can't control Connected by feeling Oh without very souls Right until it lifts us up So everyone can see We're breaking free I'm flying There's not a star in heaven that we can't reach If we're trying We're breaking free Oh, I'm breaking free You get to the place to be all that we can be Now's the time So we're breaking free We're breaking free More than how Oh, yeah, sorry, I always sing that part in those More than you more than me Of us breaking free There's not a star in heaven that we can't reach You want us to sing that you got to pay for it We're breaking free We're Get to that place to be all that we can be Now's the time So we're breaking free Oh, we're breaking free The world can see That's on so much. Have you you've heard the original right?  Hold on. So then it's uh duck tails. I'm just I'm not even doing karaoke version Not even that I Not not a full episode. We need a theme song. There it is. It's so it's so short. Here we go Like oh, this isn't the original. Hold on. We need we need the original duck bird We need the original at least get it with lyrics duck tails even though. I know you don't know the lyrics I know I know the lyrics to duck tails. I know the lyrics. It's just nice to have them.  It's just nice to have Here it is. You're ready. Yes. Yeah, you know it's why I have to put the lyrics. Yes. It's just nice to have them there Oh my god He doesn't know duck. Yeah, sir Life is like a hurricane here in duckburg Ray Scott lasers airplanes. It's a duck blur Might solve a mystery All rewrite history duck tails Every day they're out there making duck tails Tales of daring do bad good luck tails There's a danger. What's behind you? There's a stranger out to find you What to do? Just grab on to some duck tails. Whoo Every day they're out there making duck tails. Whoo tails of daring No duck tails. Whoo Yeah, I love duck tails. I know right. I forgot some of those zoos are really funky one of the black tails What is the week do I stream it is monday wednesday and friday tonight?  You're still singing Singing in the ring Hold on hold on Now that we have duck tails, I'm sorry. I know I don't I wish I had more money to give to myself Right. I wish I had more money to give myself Um dark wing duck Let's get Dark wing duck dark wing duck. I'm sorry Oh, we'll we'll go there. I don't actually remember that All right Yeah, I know Champion of the night Of all the shadows dark wing on tonight Somewhere some villains schemes, but his number's up Dark wing duck when there's trouble you call dw dark wing duck Let's get dangerous dark wing duck Dark wing dark wing duck Out of the smoke and he appears the master of surprise Little That shadow we disguise Nobody knows for sure bad guys out of luck because we have some dark wing duck We have the trouble you call dw dark.  Gotta love dark wing. Oh, yeah Oh, so good. Is there a suggested one? I love these old shows Um Goof Troop Like son, they're always number one Best pals Work things out Oh I love this Dude that movie the goofy movie. I know right? Oh my god. The goofy movie is so good The first one even the second one was all right, but the first one was awesome bonkers. Oh my god I I don't even know if I know that one. I don't know if I know bonkers very well. Oh. Oh, no Oh, yeah All right. Oh, it's actually there.  It is. Wow. I was actually just thought it You guys remember this song?  There's no case too big. No case too small When you need help just call Rescue range Where there's danger Watson and mr. Holmes have two minds so fine Looked under every stone when you need some help to save the day They're never far away And Oh, yeah This is only like the movies they have. Oh really? Yeah Chip and Dale with his danger Take the clues and find out where the chieftain is Who? Yeah, that's what the normal version means Chip and Dale Oh my gosh Okay, the bonkers thing is poppin up What is the bonkers theme? It sounds familiar There's a cat that handed it over Fudging in vain Top of the game Appetitioly hit What is this?  No ifs and buts Muckers someone's dealing the show can't you see gotta go go? The trap ready to snap is that been the cabinet taking the rap? Oh my gosh. I know this I know I don't remember the show. I don't remember the show at all. I know I know this. Oh, yeah, that's now. Yeah Now I see that Yeah, okay, there's bonkers The lost extended bonkers theme You learn how to super chat Colin Um Yeah, if you have a no if you have the YouTube app on an Android device, you can also super chat You can't super chat on on iPhones. What really? Yeah, you can't do it. It's just not available on The new adventure Yeah, yeah, yeah, none. You see it. Oh, yeah bonkers. I haven't seen her so long I Were a so I know there's no words Cartoon deep silence I don't know you better go to check I'll carry the stream. Oh, God. Fairly. I parents. Oh, okay Yeah, I want to do this one. It's really short. Yeah, I know it is Oh I'm a dead big yo is giving him commands bad tour In his room spoken instantly But it's magical and they should grant us every wish cuz in reality They are his god parents barely our parents monster wings floating counting things parents family our parents Hey pop, beepop, boopop, hot rod. Two strawberries, green waskwabba juice. Giant snake, birthday cake, long fry, chocolate shake. Ah, parents, fairly ah, parents. Flipped you in when you were a kid. You need a check card. Collins. All you need is a check card or a credit card to be able to donate for a super chat. Oh. Ah, parents, fairly ah, parents. Oh, Kalu. Oh, god. It's Kalu. I need to find a freaking charge cord for my phone. Well, that's not my phone. Oh, Rugrats. Oh, I love Rugrats. Donald Duck. Oh, God, Arthur. If you sing, you lose, child. Childhood theme songs. I'm sorry. I'm sorry. All about how my life got flipped and upside down. And I left the commandment. Sit right there. How I became a prince of a town called Bel Air. This is without lyrics, so we can't see how much we know. I want to be the very best like no one ever was. To catch them is my real test. To train them is my car. Who lives in a pineapple under the seas? I was going to get that one right. The Builder. Yeah, I know what it is for there. Oh, my God, Bob. Yes, we can. I haven't heard this in so long. Why are we going so much further than we've been joining the other ones? Oh, my God, I never watched this show. The Zack and Cody, right? Yes, we have the sweet love. Most of the time. I never watched this show. I know there were twins. I used to watch this, actually. I didn't play this to do the challenge. I played it because I wanted to sing the songs. Right? Yes. Oh, yeah. It's a proud family. Yep. I feel like who actually does the voice is pretty good. Oh, take it. You? Where are you? And we got a lot to do now. Oh, Scooby Doo. Where are you now? I love us. Yes, God. Do-do-do-do-do-do-do-do-do-do-do-do-do-do-do-do-do-do-do. Oh, yeah, doll today. Yeah, doll today. Two. Oh, God's name is the Goo House. I don't recognize the song though. I didn't watch a lot of Mare in the big wheelhouse. I've seen it I just haven't watched a lot of it. That's so raven I know the song, I don't know the words though This is old school. This is the part where you rethink your life. So sensation God, I want so much Barney when I was a little kid Barney's friends are big and small. They come to me. I Arnold Oh my god, they still make new episodes of all W's too But this isn't the song anymore. Oh dragon tails. I love dragon tails I don't remember the song though. I mean, I recognize it. I just never sang it when I was a kid Right He's saying a lot more to these Dexter's laboratory Oh, yeah, Clifford, yep, I read more of the Clifford books on the show Man, yes Love magic school bus Magic school bus No, no, they don't need to see it Oh I saw every episode of Doug I've seen every single one like twice said hey, yeah What a wonderful kind of day We can learn to love and play and get along with each other What a wonderful kind You know, that's why they had they have a cartoon show after the movie came out Needle and stitch Oh What is the show again?  I haven't seen this Oh I didn't watch this one. I've seen this show. I know I I didn't watch it, but I've seen this on TV before yeah This is why we should put this up on there. So no This should know from what kind is this metal line Yeah, yes it is yeah happen to it family Even TV No, they have it back in full Oh, it's Johnny something Johnny Johnny Johnny This is the first one I had no idea I've never seen this one I've seen this one Chris and Martin Parents fairly our parents wings floated cranny things our parents fairly our parents God So simple way I find a way I find a way If you open up your mind, I recognize yes, I'm gonna go It's a beautiful day This was so popular way back I know right look the big it was like the biggest show on TV Yes, I don't see bears Sorry barrenstain barrenstain it was never barrenstain I don't know why we always thought it was Don't worry about it man, dude, I love cartoons That's what I'm waiting for Cat dog Amanda show you Okay recess, yes recess All right, we're done we're good at the end of the stream Eric's probably already missed his food. Yeah, probably peace


We have just arrived here at Palanka border crossing and as you see behind me there is a build-up of all of the persons who want to cross over. People have been waiting for a very long while. The queues of the cars are kilometers all the way up towards Odessa so it's a quite tough situation. We have been providing basic support so they can distribute that in terms of water, some basic foodstuffs but also hygiene kits. There is also a bit of clothes here because the wind is very very harsh and to give some basic shelter to people who are coming here and waiting for a very very long time.


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Biological drugs have greatly improved the treatment of chronic inflammatory skin conditions, with a growing number of investigational drugs and small molecule inhibitors emerging as potential future prospects in the treatment of these diseases. This article was offered by Ichiyo, Astrid Helen Ravn Jorgensen and Simon Francis Thompson.


Hi, my name's Aled, and I've been having some problems with school. I don't think the school and the local authority are doing enough to help me learn or joining all the lessons and activities. I'm hoping that the special educational needs tribunal Wales, sent to, will be able to help me with that. Tribunal lease edi targ. Y poblem yn mynd i tribunal lease os edyn nhw'n anhapus am rai penderfyniadau sy'n effaithio arnyn nhw. Y ffewr mwynt sego, I was unhappy with some of the decisions the local authority made about the extra help I needed at school. I talked about it with my school and the local authority, but I felt that what they decided to do was not enough to help me. Mae tribunal lease yn debyg i ddyfarnwyr. Dydau ddim yn cymryd ochrau. Mae o'n gwneud yn siŵr bod rhyholau poisig o'r enw defddfa, wedi cael ei dilyn yn gawyr pan gafodd penderfyniadau ei gwneud. So, I decided to ask sent to to help. This is what they call making an appeal. I chose to do this myself, but my parents could have done it for me. I filled in the application form with the help of my case friend and sent it to sent to. Rhaid i tach dderbyn cais y peil o fymdoi fydd i'r ddyddiad oedd y llythau'r ganar all yn dweud o'r ddych chi a mae benderfyniad tarfynol. I had about six weeks to send them all the information about the appeal. This is called a case statement. Sent to then sent to me a copy of all the information they had received from the LA about my appeal. I also had a letter telling me where and when my meeting would be held. Mae gwrando ia'r tribunal lease yn gyfarfod drwy'n pawb sy'n rhan o'r y peil. Mae cael ei drefni gan tach. I'm going to the meeting called a hearing with sent to, where a panel of people who will listen to everything and come up with a fair legal decision. I know there will be quite a few people there. My family, my teachers, my therapist and some people from the LA who are basically bosses of education in my area. It sounds like a lot, but I know that everybody has to be heard to keep it fair, so that's okay. This is where my hearing is happening, a place outside school that I can get to easily. Sent to have chosen a place that is private and neutral for me and the school, so we feel comfortable and can talk about the things that matter. In other words, my appeal. They told me that someone from sent to will meet us when we get there and tell us a bit more about what's going to be happening today. Fel arfer, mae gwrando ia'i yn digwydd mewn lleoliad neutral fel gwestau a bydd yn breifat. Hi. Hi. You must be Aled. Yes, and this is my name. Hi. My name's Leon and I'm the clerk from sent to. Thank you for coming. How are you today? Fine, thank you. A little nervous. That's okay. There's nothing to worry about. The panel are here to listen to all the facts and make sure everybody hears what each other has to say. If you'd like to follow me, and I'll come and get you when it's time to start. Mae Clare Cotach yn cyfarfod pobl pan fydd yn un cyrraedd gwrandoiad ac yn dangos i dyn nhw ble i fynd. What time will this start? Usually about 10, so not too long now. How long will it take? It can take all day, but there'll be plenty of breaks and lunch too. You can stay for all of it, or only part of it. It's up to you. It is your hearing after all. Do you have someone to be with you if you decide not to stay in the room for the whole hearing? Yes, my auntie's coming soon. She'll look after me. That's great. I'll be back soon. Mae gwrando iawn yn cymryd trwy'r dydd weithiau. Mae'n syniad adod y game ddawel teiga yn ei lyfyr. Siŵn per a boed a diod gyda chi. If you'd all like to follow me to the hearing room then please. The first thing I notice is how many people there are in the room. This is the chairperson. He's in charge of the tribunal. He listens to what each person says and asks questions. He's also a lawyer. These two I decided upon are educational panel members. They are experts in special educational needs. These three people are respondents. She is speaking on the behalf of the LA. She is a teacher and she is a therapist. These people know how I'm getting on in school and they know a lot about my needs. They are called witnesses. This is the clerk. It's his job to make sure everyone is okay. He also records the hearing. This is my case friend. My case friend has helped me prepare for today and will help me make my points. This makes me feel a lot more relaxed about the day and I know I'll get cheered with her help. I made the appeal so I'm the appellant. I've come along today with my nana. I also bought a witness. Borodal, good morning. Welcome to the tribunal hearing. The independent body set up to hear these appeals. We have read all of the papers in your case and we've had a meeting before you came in to discuss your case. We will now hear what everyone wants to say and we will ask some questions. At the end of that, when we have heard what everyone has to say, we will have a further meeting and we will make our decision. Cadeirydd y tribunal i sydd yn gofal i emwg randawiad a bydd yn dweud os ych chi beth sy'n mynd i ddigwydd. The jail person started the day by telling us what was going to happen including when there would be breaks and time for lunch. We listened to people giving evidence. That means fact about what I needed and what the school could do about my needs and we could all ask questions. Bydd pawb yn cael amser i siarad a gofyn cwestiynau'r randawiad. Yn cennwys chi. The centre panel asked me a few questions like. So what do you like in school? And what help do you think, Alled, works best for you? I was also allowed to ask questions. The jail person made sure that everybody had a chance to speak and that we all listened to each other. It wasn't too bad in the end. Now all I have to do is wait for a decision. Bydd y tribunal i'n amlalleth yr ardych chi, iddweud beth sydd wedi ei benderfyniad ti'r daethnas ar ôl y grandawiad. It's been two weeks since the hearing and the centre panel have been busy writing out their decision very carefully. This is the letter that explains what they have decided. They told me it could be one of three decisions. Allowed, Allowed in part and dismissed. Allowed. Centre will agree with the appeal and there must be change in what the school and the local authority do. Or where I go to school. Allowed in part. This means a centre agree with some of the appeal but not all of it. There will be some changes but not all the changes we wanted. And dismissed. This means a centre don't agree with the appeal and the school and the local authority will not have to make any changes. So, I wonder what the outcome will be for me.


This is stock number 10441. We are here at Summit Automotive in Fond du Lac, Wisconsin. You're new and used heavy-duty truck and RAM headquarters. Today, we are checking out this super clean 2017 RAM 2500 mega cab short box. This truck has a 6.7 liter Cummins diesel and has been fully safety and inspected by our service shop. It has a fresh oil and filter change. All the fluids have been checked and topped off and this truck has been gone through mechanically 100% and is 100% ready to go. Granite crystal is the color we shoot all of our videos in 1080p 60 frames per second. So if you have HD capabilities on your computer, tablet, or smartphone device, turn them on right now because it is like you're right here looking at the truck with me and definitely your best way to check out the vehicle quality and condition-wise before seeing it in person. If you want to check out more pictures in the upper right hand part of the screen, a link right to our website. So click that and check us out there. It has Hostel 20 inch painted alloy rims, Nitto Trail Grappler 35 by 12 and a half R20 LT tires, and they have about half the tread left on them. It has a leveling lift kit in it right there about a 2 and a half inch and the frame and underbody is in really nice shape on this truck. This one has the Sport Appearance Package which gives you the blacked out headlight bezels, the blacked out grille and RAM logo. It has front bumper parking sensors, factory fog lights, no major dents or dings on that front bumper, passenger side fenders in nice shape, and the passenger side front rim. No scuffs or scrapes on that. As you go down this side of the truck you can see just how clean the body is, how reflective and mirror-like that paint is. We take these HD videos so if you are far away or even if you're close by and just cannot make the trip down but you're still interested in purchasing the truck, you can see the truck, hear the truck, and have confidence in the vehicle that you're looking at before you even get here, so you can make a smart buying decision from the comfort of your own home. In fact, we offer a Summit Auto Fastpass option in the upper right hand part of your screen, a link right to our website where you can apply for financing, get pre-approved, see a payment quote, even appraise a trade if you have one, all from the comfort of your own home. Frame and underbody, very clean, has all the remaining factory exhausts. This truck came out of Montana, so no rust on it, back rim, excellent shape, and the back tires have just as much tread as the front tires. See the frame and underbody back here, excellent shape as well. And as we come around to the back of the vehicle, you can see the rear bumpers in really nice condition, no major dents or dings on that. Back up parking sensors, full towing package which includes a receiver hitch, four pin and seven pin wiring, and the tailgate is in really nice shape, I didn't see any major dents or dings on that. You get the blacked out RAM logo, the blacked out 4x4 logo, the spray and bed liner, this is a turbo liner, no major dents or damage in the bed, and it does have LED bed lighting. Tailgate shuts nice and solidly, and as you go down this side of the truck, just as clean as that passenger side, take note of no dents, no dings, very clean on the box there. And this back rim is in excellent shape as well, didn't see any scuffs or scrapes on that. Down the rest of the side of the truck, very, very clean. It does have the fold out tow mirrors, so they fold out like so. They have heating elements and built into LED directional signals, they also fold in like that. And they are power-fold in, so press that button and they do fold in like so. I always like showing both sides, so you can see that both sides are working. Power windows, power locks, power mirrors. The big horn package gives you the gray cloth interior, there are no rips, there are no tears on the seats. Both of these seats are heated, power driver's seat with lumbar, and we have weather tech floor mats throughout on this truck. Auto headlamps, it's kind of funny, just about every mega cab I've ever seen has weather tech floor mats in it, not really sure why. Anyways, 50,083 miles, you get the digital speedometer, outside temp, compass, range to empty, trailer brake controller, you got all that stuff on there. Has the heated leather wrap steering wheel, cruise controls on the right, Bluetooth and information center controls on the left, and you do get audio controls on the back of the steering wheel. Comes with the six-speed automatic transmission, the AM, FM, Sirius XM radio capabilities on the A.4 touchscreen radio. This is also where your backup camera shows up. It has the heated seats and heated steering wheel controls, the backup camera. You can put your Bluetooth cell phone on here. Also, you have your climate control, and it does have dual climate control for the driver and the passenger. Down here, if you like the more tactile buttons, you can use those. Has the factory brake controller, stability control, tow haul, factory exhaust brake, and then those front and rear parking sensors, you can turn those off and on. Has a 115-volt, 150-watt plug-in, weather tech floor mat. On that side, passenger seat is very clean, has well-known rips or tears, and the headliner is in excellent shape. I don't think this truck's ever been smoked in, smells very clean inside. Has your map lights, power sign, rear window, and your home link buttons for your garage door security systems and lighting systems. And you do get 911 and assist buttons in that rear-view mirror. Those are features of the vehicle that you never have to pay a subscription for. We'll take a quick look at the back seats, and then we'll check out under the hood. The back seats are just as clean as the front seats, no rips or tears back here. You can see that these back seats actually recline a little bit, which is pretty neat. They also fold down flat, and you do get latch-tiled safety system. So they fold down two different ways. This one can go down, and you can see that the bottom of the seat folds down as well. And what you do is you get a flat surface. So if you wanted to actually take a nap back here or something, or if you got pets wanting a nice flat surface, you can put both sides down and do that. And then the other way it works is just this backrest comes down. If you need a higher shelf, I guess you could say, it works like that as well. Power slide and rear window with the built-in rear defrost, and it does have the WeatherTech floor mat back here as well. Very clean once again, and it does have the child safety locks on the back doors. We'll take a quick look under the hood. I would personally like to thank you for checking out the video today, and hopefully from this HD video, you will have been able to tell just how clean this truck is all the way around inside. Now under the hood we have the 6.7-liter Cummins diesel engine base. Very clean, runs very smooth. This truck has been fully safety and inspected by our service shop as a fresh oil and filter change. All the fluids have been checked and topped off per the state of Wisconsin inspection process, and this truck is 100% ready to go. To see more pictures of this truck, or one of our other 450 new and used cars, trucks, SUVs, minivans, Wranglers, halftones, three-quarter-tons, one-tons, you name what we got, go to our website, www.summitauto.com. Full pictures and descriptions of every single vehicle from two locations all at summitauto.com. If you'd like to check out more HD videos, you can go to www.youtube.com. Remember to like, subscribe, and share on this video and all the videos that you see there. In fact, in a second you will see a link to subscribe to our YouTube channel on your left, a link to more heavy-duty truck videos like this one on your right. If you've not been to our website, on the bottom link to this vehicle on our website, click those, check us out, and we really look forward to helping you with this super clean 2017 Ram 2500 Mega Cab Short Box Big Horn Sport Edition. Thanks again.