WEBVTT - Can cosmic rays corrupt computers? 0:00:07.840 --> 0:00:10.360 When you save that picture of your cute dog or 0:00:10.440 --> 0:00:13.360 cat on your computer, you expect it to be there 0:00:13.440 --> 0:00:15.600 later when you want to show it off or send 0:00:15.640 --> 0:00:18.840 it to your favorite podcaster. Side note, Thanks for all 0:00:18.880 --> 0:00:21.760 the pet pictures. We love them and keep them coming. 0:00:22.680 --> 0:00:25.439 But how can you be sure that the information you 0:00:25.520 --> 0:00:28.680 store in your computer will be there uncorrupted when you 0:00:28.720 --> 0:00:33.000 come back for it? Is our digital information infrastructure robust 0:00:33.400 --> 0:00:37.240 or fragile. Since this is a physics podcast, you might 0:00:37.280 --> 0:00:40.080 be wondering if there are physics reasons that your data 0:00:40.240 --> 0:00:44.519 might not be safe. There are in this case. Unfortunately, 0:00:44.640 --> 0:00:48.400 it's not aliens. I'd love if it were aliens. But 0:00:48.520 --> 0:00:53.519 the concern is radiation from space. We know that it 0:00:53.520 --> 0:00:56.279 can hurt our bodies and rewrite our DNA, which are 0:00:56.360 --> 0:01:01.280 essentially biological hard drives. Can it also erupt our computers 0:01:01.400 --> 0:01:05.560 cosmic ray bitflips? What does that mean for data centers 0:01:05.600 --> 0:01:09.440 in space or puppies in space or pictures of cats 0:01:09.480 --> 0:01:14.560 on Mars? Oh my? Welcome to Daniel and Kelly's Extraordinary 0:01:14.680 --> 0:01:15.720 Digital Universe. 0:01:28.920 --> 0:01:32.040 Hello. I'm Kelly water Smith. I study parasites and space, 0:01:32.120 --> 0:01:34.360 and if something goes wrong with my computer, I have 0:01:34.520 --> 0:01:35.679 no clue how to deal with it. 0:01:38.720 --> 0:01:42.160 Hi, I'm Daniel. I'm a particle physicist and I'm technically 0:01:42.200 --> 0:01:45.000 an experimental list but really all of my sciences on 0:01:45.120 --> 0:01:45.679 the computer. 0:01:46.200 --> 0:01:48.560 Now, you told me that you were thinking about going 0:01:48.600 --> 0:01:51.800 into computer science before you decided to go into particle physics. 0:01:52.200 --> 0:01:54.760 So are you the person that everyone goes to when 0:01:54.760 --> 0:01:57.920 they have computer problems or now in the era of 0:01:58.000 --> 0:02:00.560 like MacBooks, is it just like two hard for you 0:02:00.600 --> 0:02:03.200 to troubleshoot? Or yeah? Are you? Are you the go 0:02:03.240 --> 0:02:03.760 to person? 0:02:04.000 --> 0:02:07.200 I'm definitely the tech support person in my family. You know, 0:02:07.640 --> 0:02:09.800 why won't this thing load? Or I want to print 0:02:09.800 --> 0:02:12.440 from here? Why can't I? For some reason, everybody comes 0:02:12.480 --> 0:02:15.880 to me, even though like computer science undergraduate degrees is 0:02:15.919 --> 0:02:18.520 mostly about like red black trees and sorting and whatever, 0:02:18.600 --> 0:02:21.080 and you don't really get expertise in that kind of stuff. 0:02:21.200 --> 0:02:25.720 Nothing useful, nothing useful exactly. But you have very recently 0:02:25.760 --> 0:02:28.440 become aware of how fragile computers are. 0:02:28.600 --> 0:02:33.120 Sure, Yes, I'm coming to you from Zex's chromebook because 0:02:33.120 --> 0:02:36.919 I have with in one year, broken my computer screen 0:02:36.960 --> 0:02:39.320 for the second time and it is in the shop again. 0:02:39.560 --> 0:02:41.720 And have you managed to blame this on like weird 0:02:41.760 --> 0:02:42.880 particles from space. 0:02:43.600 --> 0:02:48.079 No, no, what, just a lot of clumsy members in 0:02:48.120 --> 0:02:51.840 the Wienersmith household. Fifty percent of the time it was 0:02:51.880 --> 0:02:54.920 my fault. The other fifty percent was my adorable children. 0:02:57.520 --> 0:02:59.680 Well, maybe today's episode is going to give somebody over 0:02:59.720 --> 0:03:02.560 there excuse I didn't break that computer screen, even if 0:03:02.560 --> 0:03:04.720 my footprint is on it. It was cosmic rays. 0:03:05.400 --> 0:03:08.280 In this case, it was their teeth marks. But yes, 0:03:08.360 --> 0:03:11.320 maybe maybe they can blame a really amazing combination of 0:03:11.360 --> 0:03:13.480 particle rays that came in just the right pattern. 0:03:14.880 --> 0:03:17.000 Well, today's topic really connects with a few of my 0:03:17.120 --> 0:03:20.280 interests because, of course I like thinking about cosmic rays. 0:03:20.320 --> 0:03:23.400 They are particles from space, and everything I do is 0:03:23.639 --> 0:03:26.600 on the computer. Plus, this is a concept that appears 0:03:26.600 --> 0:03:30.639 a lot in popular science, cosmic rays flipping bits on computers, 0:03:30.919 --> 0:03:33.160 And I thought, let's make sure everybody out there really 0:03:33.200 --> 0:03:36.240 understands how that works and how serious a problem it is, 0:03:36.600 --> 0:03:40.480 especially with all this talk of sending data centers into space. 0:03:40.880 --> 0:03:42.600 Does it occur a lot in pop science? I can't 0:03:42.640 --> 0:03:43.680 think of a single example. 0:03:44.160 --> 0:03:46.480 Wow, maybe I read the wrong pop science. 0:03:47.200 --> 0:03:50.880 Or maybe I read the wrong pop science. Can you 0:03:51.000 --> 0:04:00.360 name five examples? No? I'm just kidding. Name one. I'm 0:04:00.400 --> 0:04:01.480 winny h. 0:04:04.240 --> 0:04:06.120 You put me on the spot, and I cannot name 0:04:06.160 --> 0:04:08.320 a single one right now off the top of my head. 0:04:08.560 --> 0:04:10.840 But I have the feeling like this is something that 0:04:10.920 --> 0:04:14.000 I hear a lot in popular science, or that people 0:04:14.080 --> 0:04:17.440 in general know a little bit about, but my benefit 0:04:17.440 --> 0:04:20.840 from understanding, like the real physics that underlies all of 0:04:20.880 --> 0:04:23.080 this stuff, so that in the future, when there is 0:04:23.080 --> 0:04:25.720 an onslaught of popular science articles after we launched the 0:04:25.760 --> 0:04:29.400 first data centers into space, everyone will be well equipped. 0:04:29.480 --> 0:04:31.640 Well, but I mean, this is a thing that could 0:04:31.640 --> 0:04:35.400 be important for our lives personally, So like, not only 0:04:35.440 --> 0:04:38.240 could this be important if we put data centers in space, 0:04:38.279 --> 0:04:40.760 but for example, one of our listeners, Simon, sent us 0:04:40.760 --> 0:04:43.120 this article where there was a plane that was flying 0:04:43.160 --> 0:04:46.640 and all of a sudden it dropped really fast, and 0:04:46.680 --> 0:04:49.400 nobody died. Some people did get hurt. But the thought 0:04:49.480 --> 0:04:51.960 was that some part of the computer on the plane 0:04:52.000 --> 0:04:54.000 got hit by a cosmic ray. It flipped a bit, 0:04:54.040 --> 0:04:56.799 which Daniel's going to explain, and that sort of messed 0:04:56.839 --> 0:04:59.240 up the control of the plane and the plane dropped 0:04:59.279 --> 0:05:02.000 really quick and some people got hurt. And so this 0:05:02.160 --> 0:05:04.640 is like a thing that could impact our lives, and 0:05:04.680 --> 0:05:07.000 at some point I have another space related story that 0:05:07.040 --> 0:05:09.280 I'll tell. So you know, this isn't just a thing 0:05:09.320 --> 0:05:10.920 that might be important in the future. It's a thing 0:05:10.920 --> 0:05:11.640 that matters. Now. 0:05:11.960 --> 0:05:13.960 Hey, that sounds a lot to me like a popular 0:05:14.000 --> 0:05:15.880 science article about a cosmic ray. 0:05:15.920 --> 0:05:20.360 Bitflip, I thought you said a sci fi thing. 0:05:20.440 --> 0:05:25.360 Oh are you too popular? No play the tape, we said, 0:05:25.400 --> 0:05:30.479 POPSI this is a concept that appears a lot in 0:05:30.600 --> 0:05:31.360 popular science. 0:05:31.400 --> 0:05:32.800 Does it occur a lot in pop science? 0:05:32.800 --> 0:05:39.920 Pop science? Popular science? Pop science, popular science, popular science articles? Oh? 0:05:40.040 --> 0:05:43.480 I thought you said sci fi? All right? All right, anyway, 0:05:43.600 --> 0:05:46.000 Daniel and I aren't communicating well today, But that's all right. 0:05:46.000 --> 0:05:48.320 We're gonna move forward. I'll give you the win on 0:05:48.360 --> 0:05:51.920 that one, all right. So let's let's lay some groundwork here. 0:05:52.080 --> 0:05:54.400 But before we explain how everything works. I was wondering 0:05:54.440 --> 0:05:58.160 what people knew about how cosmic rays could mess up 0:05:58.160 --> 0:06:00.880 those pictures of your puppies. So I went out there 0:06:00.920 --> 0:06:04.560 to ask our volunteers their thoughts, without any googling, of course, 0:06:04.800 --> 0:06:09.520 whether cosmic rays can corrupt computers. Here's what people had 0:06:09.560 --> 0:06:10.040 to say. 0:06:10.240 --> 0:06:12.800 Perhaps theris magnetosphere is protecting us from that issue. 0:06:12.960 --> 0:06:15.200 Cosmic rays are nasty. 0:06:15.440 --> 0:06:19.800 Of course, Cosmic rays can corrupt computer data. Cosmic rays 0:06:19.800 --> 0:06:22.400 definitely can flip bits in computer systems. 0:06:22.520 --> 0:06:25.240 I'm sure cosmic rays can cause problems or another. I 0:06:25.400 --> 0:06:28.560 can with some dish drawers. I'm not sure. 0:06:29.000 --> 0:06:33.720 Cosmic rays can absolutely corrupt computer data by flipping essential bits, 0:06:33.920 --> 0:06:36.479 even when we build in redundancy. I think there have 0:06:36.600 --> 0:06:41.400 even been stories of car accidents attributed to cosmic ray disruptions. 0:06:41.640 --> 0:06:46.680 I would think so because the higher frequency spectrum could 0:06:46.720 --> 0:06:50.800 penetrate I wouldn't imagine across the computer barriers. 0:06:50.920 --> 0:06:54.040 Cosmic rays and computers do not get along. I think 0:06:54.080 --> 0:06:57.600 cosmic rays messing with our computers all the time, and 0:06:57.640 --> 0:07:00.440 that's why we have checksums and stuff. Yes, I know 0:07:00.480 --> 0:07:03.880 for certain in space, electronics that are exposed to cosmic 0:07:03.920 --> 0:07:06.919 rays do have a risk of that bits getting flipped. 0:07:07.120 --> 0:07:11.800 Absolutely, cosmic rays can corrupt data. Satellites can be corrupted 0:07:11.800 --> 0:07:16.080 by cosmic rays, so they have to be hardened and redundant. 0:07:16.200 --> 0:07:18.360 I'm not sure about on the surface of the Earth, though, 0:07:18.680 --> 0:07:22.280 a cosmic ray flipped a bit inside the game as 0:07:22.320 --> 0:07:27.320 the player was playing and basically cheated for them. They 0:07:27.440 --> 0:07:31.240 would be able to alter the bit in a data stream. 0:07:31.280 --> 0:07:35.040 So yes, great answers. As always, I think when someone 0:07:35.080 --> 0:07:39.400 says can X mess up y, my answer is usually yeah, 0:07:39.440 --> 0:07:43.120 probably as like I'm negative. But I don't think I 0:07:43.200 --> 0:07:45.280 really knew that this was something to worry about until 0:07:45.320 --> 0:07:48.120 I was researching a city on Mars and we came 0:07:48.160 --> 0:07:51.520 across some stories about like space radiation messing up computers. 0:07:52.560 --> 0:07:55.560 Yeah. People think of their computers as robust, like you 0:07:55.560 --> 0:07:58.160 put a one in memory somewhere, it's going to be there. 0:07:58.560 --> 0:08:01.400 It's not like somethuzz if you a paper that can 0:08:01.440 --> 0:08:05.040 get overwritten or destroyed or whatever. But in reality, these 0:08:05.040 --> 0:08:07.760 are physical systems and they live in the universe, and 0:08:07.800 --> 0:08:10.480 the universe is not always a friendly place to store 0:08:10.520 --> 0:08:11.240 to your data. 0:08:11.360 --> 0:08:13.160 Yeah, and you're not supposed to bite the screen either. 0:08:15.600 --> 0:08:19.120 So let's start with understanding how computers store data because 0:08:19.160 --> 0:08:22.040 I still find this like slightly magical, which which is 0:08:22.120 --> 0:08:25.280 kind of great. So how are computers storing information? 0:08:25.760 --> 0:08:29.120 Yeah, it's a great question, and fundamentally computer store information 0:08:29.240 --> 0:08:33.000 using quantum mechanics. Right, you could store information on just 0:08:33.040 --> 0:08:35.360 like a long tape, like the way a Turing machine does. 0:08:35.400 --> 0:08:37.679 You're like writing ones and zeros and principle, it can 0:08:37.760 --> 0:08:40.240 be anything, but you want it to be compact, so 0:08:40.320 --> 0:08:42.079 you could have like lots and lots of ones and 0:08:42.160 --> 0:08:44.880 zeros and not have it take up a whole room. 0:08:45.120 --> 0:08:46.839 And you want it to be fast so you can 0:08:46.880 --> 0:08:49.160 read it out really quickly and you're not waiting an 0:08:49.240 --> 0:08:52.040 hour for that picture of your puppies to load. And 0:08:52.120 --> 0:08:55.599 so we make it small and fast by using atomic systems. 0:08:56.080 --> 0:08:58.400 And at its core, all these atomic systems are built 0:08:58.400 --> 0:09:01.360 on semiconductors, which is why you hear about silicon so much. 0:09:01.400 --> 0:09:05.360 Silicon is a semiconductor. Well, what does that mean semiconductors, Well, 0:09:05.360 --> 0:09:10.840 semiconductors sit between insulators which don't conduct electricity and conductors 0:09:11.160 --> 0:09:14.400 like metals, which conduct a lot of electricity. And understand 0:09:14.400 --> 0:09:16.200 why that is. You have to understand something about the 0:09:16.240 --> 0:09:19.360 atomic structure here, and we're used to thinking about atoms 0:09:19.400 --> 0:09:23.400 by themselves. You have like energy levels, and a silicon 0:09:23.440 --> 0:09:25.679 atom has like where electrons can be. There's like a 0:09:25.760 --> 0:09:29.079 ladder of them, right, and they can absorb and emit photons. 0:09:29.120 --> 0:09:31.040 This kind of stuff is like a very discrete set 0:09:31.080 --> 0:09:34.280 of energy levels, and that's true for atoms. And if 0:09:34.280 --> 0:09:36.640 you have, like a gas of silicon, it's going to 0:09:36.720 --> 0:09:39.360 emit photons at certain energy levels and absorb at those 0:09:39.480 --> 0:09:42.240 energy levels, and that's all cool. So that's atomic physics. 0:09:42.440 --> 0:09:45.640 Is atomic physics another word for chemistry, because it kind 0:09:45.679 --> 0:09:48.200 of sounds like it's another word for chemistry. 0:09:48.400 --> 0:09:51.200 It's the foundation of all chemistry. Yet everything in chemistry 0:09:51.240 --> 0:09:53.760 comes out of those energy levels. And then it gets 0:09:53.800 --> 0:09:56.520 more complicated because you have atoms binding with each other 0:09:56.600 --> 0:10:00.520 and sharing electrons. And if you take that too, you 0:10:00.559 --> 0:10:02.880 get things like solids where you have a whole lattice 0:10:02.920 --> 0:10:05.200 of atoms, and now you don't have to solve these 0:10:05.200 --> 0:10:07.000 problems just for one electron. You have to think about 0:10:07.040 --> 0:10:11.000 what happens to an electron that's shared among many, many atoms. 0:10:11.440 --> 0:10:14.480 And so instead of thinking about a lattice of silicon, 0:10:14.520 --> 0:10:17.240 atoms is like each a bunch of individual atoms with 0:10:17.320 --> 0:10:21.520 their own energy levels. These things overlap because they're so close, 0:10:21.559 --> 0:10:26.280 and so they spread these sharp atomic energy levels into bands. 0:10:26.520 --> 0:10:29.240 So we talked about bands of electron energy levels. So 0:10:29.240 --> 0:10:31.720 you shouldn't think about electron in a piece of silicon 0:10:31.880 --> 0:10:34.240 is like this one belongs to that atom, or belongs 0:10:34.240 --> 0:10:36.719 to this atom, or belongs to this other atom. It 0:10:36.840 --> 0:10:41.600 moves smoothly right the ions the nuclei are bound together, 0:10:41.640 --> 0:10:43.520 they're sort of like fixed in a lattice, and the 0:10:43.520 --> 0:10:47.000 electrons are all moving around, and there's different energy levels there, 0:10:47.120 --> 0:10:49.720 which roughly get grouped into two different kinds of bands. 0:10:50.120 --> 0:10:53.040 There's the valence bands. Those are the low energy ones 0:10:53.040 --> 0:10:55.800 where the electrons are mostly local and bound to a 0:10:55.840 --> 0:10:59.480 specific ion. But then there's above that, there's the conduction band, 0:11:00.200 --> 0:11:03.720 are usually empty and the electrons can flow around. So 0:11:04.000 --> 0:11:06.640 if you have, for example, a metal, then there's a 0:11:06.800 --> 0:11:10.160 very small gap between the valiance band and the conduction band, 0:11:10.520 --> 0:11:13.240 and the electrons that fill up the valance band can 0:11:13.320 --> 0:11:15.520 jump up to the conduction band like getting on the 0:11:15.559 --> 0:11:19.040 highway really easily, and flowing all around the metal. So 0:11:19.080 --> 0:11:21.560 if you put an electric field near a conductor, the 0:11:21.640 --> 0:11:24.559 electrons will jump up to the conduction band and flow 0:11:24.600 --> 0:11:27.560 all around. If you have a big gap there, like 0:11:27.679 --> 0:11:30.400 no entrances to your freeway, then the electrons are all 0:11:30.440 --> 0:11:32.600 stuck in their local area, and even if you put 0:11:32.600 --> 0:11:35.120 an electric field over it, they're really not going to move. 0:11:35.679 --> 0:11:39.320 So that's how to understand an insulator and a conductor 0:11:39.440 --> 0:11:42.920 or something we call a metal. Usually a semiconductor like silicon, 0:11:43.240 --> 0:11:45.680 is something where that gap is sort of like in between. 0:11:45.800 --> 0:11:49.120 It's not really big, it's not really small. All that 0:11:49.280 --> 0:11:53.000 silicon lithography helps you do some fancy local chemistry to 0:11:53.080 --> 0:11:57.800 make a silicon dioxide or silicon nitride that changes its conductivity, 0:11:57.840 --> 0:12:00.920 which means you can now separate components and dielectrics and 0:12:00.920 --> 0:12:03.559 whatever you need to build circuits. And so you can 0:12:03.600 --> 0:12:08.240 design really really small electrical circuits just by doping the 0:12:08.240 --> 0:12:09.560 silicon in various ways. 0:12:10.000 --> 0:12:13.360 Okay, so the reason you want to use silicon is 0:12:13.400 --> 0:12:17.280 because it's helpful to have something that's in between, because 0:12:17.320 --> 0:12:21.520 you well, so, like, why wouldn't you just want to 0:12:21.640 --> 0:12:25.600 have a full insulator or a full conductor on your 0:12:25.679 --> 0:12:29.600 chip as opposed to just using silicon everywhere and then 0:12:29.640 --> 0:12:33.400 tinkering with it. Tinkering sounds possibly more complicated than just 0:12:33.800 --> 0:12:35.440 putting conductors in some places. 0:12:35.840 --> 0:12:38.720 Yeah, you could construct it out of just conductors wrapped 0:12:38.720 --> 0:12:42.280 in insulators, and that's basically how you build circuits on 0:12:42.320 --> 0:12:45.680 your bench, Right, you have like copper wires wrapped in rubber, right, 0:12:45.720 --> 0:12:47.680 and that works, But it's really hard to do that 0:12:47.720 --> 0:12:51.120 at a micro scale. To manufacture that stuff, and to 0:12:51.200 --> 0:12:54.400 do it cheaply and at high volume. It's easier to 0:12:54.440 --> 0:12:57.160 take silicon, which can be tweaked in either direction. It 0:12:57.200 --> 0:12:58.880 turns out to be a lot easier to tweak it 0:12:58.960 --> 0:13:01.679 than to just like build it from scratch, okay. 0:13:01.400 --> 0:13:03.400 And so to tweak it, you just like flick some 0:13:03.480 --> 0:13:06.240 germanium on it, and now you're good. 0:13:06.640 --> 0:13:09.560 Yeah. Essentially we have a whole episode about how silicon 0:13:09.600 --> 0:13:12.120 lithography works, and people should dig into the details there. 0:13:12.240 --> 0:13:14.679 There's a lot of nuance that's missed in this summary here, 0:13:14.920 --> 0:13:17.360 but roughly, that's why you want to start with silicon, 0:13:17.400 --> 0:13:20.000 because you can easily change it to be a conductor 0:13:20.160 --> 0:13:20.920 or an insulator. 0:13:21.120 --> 0:13:24.640 I'll go check that out. My memory is just the 0:13:24.760 --> 0:13:27.760 pits lately, Okay. So now we've got our semiconductors. 0:13:27.840 --> 0:13:29.400 Yeah, and so you can use that to build all 0:13:29.400 --> 0:13:32.120 sorts of microscopic bits of your circuits out of silicon. 0:13:32.360 --> 0:13:34.839 But keep that in mind for later when we're talking 0:13:34.840 --> 0:13:37.320 about what happens when a cosmic ray tears through a 0:13:37.360 --> 0:13:40.640 piece of silicon. So, now you have the silicon, and 0:13:40.640 --> 0:13:42.120 then you want to build a computer, how do you 0:13:42.160 --> 0:13:44.920 actually use it to store memory? So your computer has 0:13:44.960 --> 0:13:48.480 several different kinds of memory depending on your need. So 0:13:48.520 --> 0:13:51.320 the memory you might think about are things like RAM. Right, 0:13:51.360 --> 0:13:54.400 These are like things your computer remembers when it's turned on, 0:13:54.960 --> 0:13:57.440 but if your turn off, the computer is empty. So 0:13:57.640 --> 0:14:00.520 like loading a program into memory so that your computer 0:14:00.559 --> 0:14:02.880 can run it. Right. So this is you know, random 0:14:02.920 --> 0:14:06.679 access memory, and these days it's called d RAM dynamic 0:14:07.080 --> 0:14:10.360 random access memory. And random access just means that you 0:14:10.400 --> 0:14:13.000 can like get a piece of informmation from anywhere. You 0:14:13.000 --> 0:14:15.439 don't have to like read it in order, like a book. 0:14:15.480 --> 0:14:17.640 You can just have an index. You can say, tell 0:14:17.679 --> 0:14:20.520 me what's stored here, tell me what's stored there. Song. 0:14:20.560 --> 0:14:22.480 As you know the index, you can look it up. 0:14:22.960 --> 0:14:26.600 Okay, So I've got a semiconductor which allows me to 0:14:26.680 --> 0:14:29.040 move electrons around. 0:14:29.560 --> 0:14:32.560 And to build circuits. And so now the question is 0:14:32.720 --> 0:14:35.880 how do you use little electrical circuits to store information? 0:14:36.600 --> 0:14:40.440 And so DRAM does this by using a capacitor connected 0:14:40.440 --> 0:14:43.520 to a transistor. So a capacitor physically, if you build 0:14:43.600 --> 0:14:46.720 a large one, is just like two surfaces insulated from 0:14:46.760 --> 0:14:49.400 each other that are separated, and so you can have 0:14:49.560 --> 0:14:52.160 like a charge stored across them. You can put a 0:14:52.160 --> 0:14:54.760 bunch of electrons on one side and then you have 0:14:54.880 --> 0:14:58.360 like a voltage across the capacitor. And so capacitor is 0:14:58.560 --> 0:15:01.160 very useful for all sorts of things circuits. But in 0:15:01.200 --> 0:15:03.280 this case you can just ask like, well, is there 0:15:03.360 --> 0:15:04.880 voltage on it? If so, I'm going to call that 0:15:04.880 --> 0:15:07.280 a one. If there's no voltage across it, I'm going 0:15:07.320 --> 0:15:09.560 to call that a zero. You just need some sort 0:15:09.600 --> 0:15:12.800 of microscopic state which you can control and you can 0:15:12.880 --> 0:15:15.160 read out, and then you assign the meaning of one 0:15:15.440 --> 0:15:17.520 to one of the states and zero to the other state. 0:15:17.720 --> 0:15:19.920 Okay, but so what could actually be happening in the 0:15:19.960 --> 0:15:22.840 capacitor is there's a lot of different ways that you 0:15:22.840 --> 0:15:25.440 could have more charge on one side and less charge 0:15:25.480 --> 0:15:28.080 on the other, but it all gets sort of summarized 0:15:28.120 --> 0:15:29.120 down to one in zero. 0:15:29.400 --> 0:15:32.480 Yeah, exactly, because this is digital logic. In the end, 0:15:32.560 --> 0:15:35.880 everything is analog, like the universe is mostly analog, but 0:15:35.920 --> 0:15:38.840 we assign digital meaning to it. And as these things 0:15:38.920 --> 0:15:42.520 get smaller and faster than the amount of charge to 0:15:42.560 --> 0:15:45.600 capacitor holds gets really really small, so that it's quick 0:15:45.600 --> 0:15:48.200 to read out, it's quick to assign, and it's easy 0:15:48.240 --> 0:15:50.240 to make small. So in this case, it's like a 0:15:50.240 --> 0:15:53.960 few tens of thousands of electrons hold the charge. And 0:15:54.000 --> 0:15:56.120 you can imagine more complicated systems. If you don't want 0:15:56.160 --> 0:15:58.800 to use binary logic, you want to use trinary, you 0:15:58.840 --> 0:16:01.480 could have like two different threashs. You could say zero 0:16:01.680 --> 0:16:04.400 is anywhere from zero to ten thousand electrons, and a 0:16:04.440 --> 0:16:07.000 one is ten thousand to twenty thousand electrons, and anything 0:16:07.000 --> 0:16:09.280 above twenty thousand I'm gonna call it two if you 0:16:09.320 --> 0:16:12.200 have trinary logic, but we use binary. So it's like 0:16:12.360 --> 0:16:16.000 zero or somewhere above ten thousand electrons or ten to 0:16:16.000 --> 0:16:19.880 thirty fempto coulums. And so there's a capacitor that holds 0:16:19.880 --> 0:16:23.000 it and then a transistor which allows you access to it. 0:16:23.240 --> 0:16:26.720 And so that's the basis of DRAM. And this requires 0:16:26.800 --> 0:16:29.960 constant power. When you turn off the computer, that charge 0:16:29.960 --> 0:16:32.520 dissipates and it's gone, which is why when you turn 0:16:32.560 --> 0:16:35.080 off your computer, it doesn't remember anymore what was in 0:16:35.120 --> 0:16:35.720 its memory. 0:16:36.160 --> 0:16:39.920 Okay, so you've got the semiconductor, and those electrons are 0:16:40.120 --> 0:16:44.440 jumping up into the highway and they're getting moved around 0:16:44.720 --> 0:16:47.320 in the capacitor so that they can store up these 0:16:47.320 --> 0:16:49.040 ones in these zeros. 0:16:48.840 --> 0:16:51.280 And it's critical there that you have conductors, Like the 0:16:51.320 --> 0:16:53.960 plates on the capacity are made of conductors and insulators 0:16:54.000 --> 0:16:57.240 between the plates so that the chargers don't just flow across. 0:16:58.240 --> 0:17:00.080 Okay, all right, so you want them to move and 0:17:00.080 --> 0:17:01.400 then you want them to stay once you've. 0:17:01.240 --> 0:17:05.400 Moved there, exactly, Okay, exactly, But these things don't work great. 0:17:05.600 --> 0:17:07.880 Like there's a leakage there because these things are super 0:17:07.960 --> 0:17:10.919 duper small and the insulator isn't perfect, and so every 0:17:11.040 --> 0:17:14.840 sixty four milliseconds or so, it just like leaks away. 0:17:15.359 --> 0:17:18.840 So your computer has to constantly refresh your RAM every 0:17:18.880 --> 0:17:22.040 sixty milliseconds or so, it rewrites the number onto it. 0:17:22.040 --> 0:17:23.120 It's not very stable. 0:17:23.200 --> 0:17:25.479 That doesn't sound like a great system. I mean, I 0:17:25.480 --> 0:17:28.120 mean it seems to work great. I love my computer 0:17:28.240 --> 0:17:29.280 when it's not in the shop. 0:17:29.359 --> 0:17:30.960 It's kind of amazing that it works as well as 0:17:31.000 --> 0:17:32.840 it does. You don't just like call up a picture 0:17:33.280 --> 0:17:34.840 and it's like totally corrupted. 0:17:35.040 --> 0:17:35.280 Yeah. 0:17:35.359 --> 0:17:38.560 Then there's another kind of memory, which is in your CPU. 0:17:38.640 --> 0:17:41.359 So your computer basically has like a hard drive to 0:17:41.359 --> 0:17:44.440 store information. And then there's the CPU, the central processing 0:17:44.520 --> 0:17:47.440 unit that does all the actual calculations. Then it has 0:17:47.520 --> 0:17:50.080 access to the main memory that we just talked about, 0:17:50.119 --> 0:17:52.600 the RAM, But when it's doing the calculations, it slurps 0:17:52.600 --> 0:17:56.560 stuff from the RAM into a special super fast memory 0:17:56.600 --> 0:17:59.400 called the CASH, which is close to the CPU so 0:17:59.440 --> 0:18:01.000 that it doesn't have to go all the way to 0:18:01.040 --> 0:18:03.359 memory which turns out to be a little bit slow. 0:18:03.680 --> 0:18:06.000 So you have these hierarchies of memory in your computer 0:18:06.400 --> 0:18:09.760 which are smaller and faster or bigger and slower. So 0:18:09.920 --> 0:18:13.360 SRAM is the fastest, smallest memory. It's like right there 0:18:13.440 --> 0:18:15.800 next to the CPU. It's like if you're trying to 0:18:15.800 --> 0:18:18.040 do your household budget, you don't keep all of the 0:18:18.080 --> 0:18:19.959 information right in front of you. You have like a 0:18:19.960 --> 0:18:22.000 sheet of paper or a spreadsheet with like the critical 0:18:22.040 --> 0:18:24.480 details right in front of you that you're calculating right now. 0:18:24.880 --> 0:18:27.240 The CPU's CASH is essentially like its. 0:18:27.119 --> 0:18:32.159 Little worksheet and sm SRAM stands for is that slow 0:18:32.320 --> 0:18:34.240 random access memory? Is that what it stands for. 0:18:35.920 --> 0:18:39.600 It stands for a static random access memory, okay, as 0:18:39.600 --> 0:18:42.359 opposed to dynamic, which is the kind you have for 0:18:42.880 --> 0:18:46.680 your most of your memory. And this is cool because 0:18:46.720 --> 0:18:50.000 it's built by a pair of logic gates usually, so 0:18:50.040 --> 0:18:53.520 it's built using not gates. Sont gits are something where 0:18:53.520 --> 0:18:55.680 if you take in a one, you output a zero, 0:18:56.000 --> 0:18:57.960 if you take in a zero, you output a one. 0:18:58.280 --> 0:19:00.560 So it's like a basic logic gate in the same 0:19:00.600 --> 0:19:03.960 categories like and gates you know that require two ones 0:19:04.000 --> 0:19:06.800 to output a one, or an ore gate that requires 0:19:07.080 --> 0:19:09.840 either of the inputs to be one to output a one. 0:19:09.920 --> 0:19:10.720 Oh yes, of course. 0:19:11.720 --> 0:19:14.640 And these again are built on top of transistors which 0:19:14.680 --> 0:19:17.040 are made of silicon, So you can tie a few 0:19:17.040 --> 0:19:19.600 transistors together to make a nand gate or an and 0:19:19.880 --> 0:19:22.959 gate or a knot gate. All these basic digital logics 0:19:22.960 --> 0:19:25.200 are built on top of the same fundamental technology, which 0:19:25.200 --> 0:19:28.679 are silicon transistors which have these various levels of doping 0:19:28.760 --> 0:19:31.439 so they can do what they need to do. And 0:19:31.480 --> 0:19:33.840 so the way SRAM works is you have two knock 0:19:33.840 --> 0:19:36.679 gates looped on each other. It's kind of silly, but 0:19:36.720 --> 0:19:39.159 it works really amazingly well. Like, say I have two 0:19:39.240 --> 0:19:41.920 knock gates. If the first one has an output value 0:19:41.960 --> 0:19:44.639 of one, and then you feed that into the second one, 0:19:44.760 --> 0:19:46.240 the second one is going to have an output value 0:19:46.280 --> 0:19:48.760 of zero, right, feed the output of the second one 0:19:48.800 --> 0:19:52.120 back into the first one, and it's going to keep 0:19:52.160 --> 0:19:55.120 the first one having an output value of one because 0:19:55.160 --> 0:19:57.199 it's input with zero. And so it's just sort of 0:19:57.200 --> 0:19:59.560 like if you have two of these things in series 0:19:59.680 --> 0:20:02.240 and then looped on each other, they support each other, 0:20:02.840 --> 0:20:05.760 and there's two stable states here. Either the first one 0:20:05.800 --> 0:20:07.800 is one and the second one is zero, or the 0:20:07.800 --> 0:20:09.560 first one is zero and the second one is one, 0:20:10.080 --> 0:20:13.120 and either way they just constantly support each other, confirming 0:20:13.119 --> 0:20:13.520 each other. 0:20:13.760 --> 0:20:16.000 Okay, I'm following, but I feel like the big picture 0:20:16.040 --> 0:20:19.640 here for anyone who is maybe having a little trouble following, 0:20:20.119 --> 0:20:22.560 is that in all of these cases, what's happening is 0:20:22.560 --> 0:20:26.359