WEBVTT - How Flash Drives Work 0:00:04.400 --> 0:00:07.800 Welcome to tech Stuff, a production from I Heart Radio. 0:00:11.800 --> 0:00:14.280 Hey there, and welcome to tech Stuff. I'm your host, 0:00:14.360 --> 0:00:18.000 Jonathan Strickland. I'm an executive producer with I Heart Radio 0:00:18.160 --> 0:00:21.480 and how the tech are you? I received a request 0:00:21.760 --> 0:00:25.760 to talk about flash memory from a hardware engineer, musician, 0:00:25.960 --> 0:00:30.639 and self described total nerd via the I heart Radio 0:00:30.680 --> 0:00:35.160 app talk back feature. Uh. That's that little microphone icon 0:00:35.320 --> 0:00:37.199 you would see if you were to navigate to the 0:00:37.240 --> 0:00:40.360 tech Stuff podcast page on the I heart Radio app. 0:00:40.680 --> 0:00:42.400 If you click on that, you can leave a voice 0:00:42.400 --> 0:00:44.879 message up to thirty seconds long there, and if you 0:00:44.920 --> 0:00:46.800 want me to include the audio in an episode, you 0:00:46.800 --> 0:00:49.080 can let me know. I always prefer opt in rather 0:00:49.120 --> 0:00:52.560 than opt out. This particular voice message did not ask 0:00:52.920 --> 0:00:55.280 for it to be used in an episode, so I'm 0:00:55.320 --> 0:00:56.880 just leaving it out to be on the safe side. 0:00:56.880 --> 0:01:01.440 But let's talk about flash memory now. One thing that 0:01:01.480 --> 0:01:03.560 we need to clear up is when we talk about 0:01:03.600 --> 0:01:08.840 flash memory, we're typically talking about data storage, you know, 0:01:09.000 --> 0:01:12.280 like like a hard drive, rather than talking about something 0:01:12.319 --> 0:01:17.399 like traditional computer memory like RAM. RAM stands for random 0:01:17.520 --> 0:01:21.800 access memory. Computer memory, as we typically define it means 0:01:21.840 --> 0:01:26.280 a temporary storage system that holds data and instructions that 0:01:26.560 --> 0:01:30.920 a CPU or central processing unit needs when it's running 0:01:31.000 --> 0:01:34.839 a particular process. Computer memory is what saves a processor 0:01:34.880 --> 0:01:39.119 from having to retrieve specific information from long term storage 0:01:39.560 --> 0:01:43.720 over and over and Without RAM, computers would be much 0:01:43.800 --> 0:01:46.119 much slower than they are. And it's why some folks 0:01:46.160 --> 0:01:48.760 will say that one way to speed up your computer 0:01:49.200 --> 0:01:52.200 is to add more memory. It actually gets way more 0:01:52.280 --> 0:01:54.720 complicated than that, though, and I'm sure I'll talk about 0:01:54.720 --> 0:01:56.960 that in another episode. Maybe I'll do an episode about 0:01:57.680 --> 0:02:01.360 the the components in your machine that determine how quickly 0:02:01.480 --> 0:02:04.360 it runs, because there's a lot of There are a 0:02:04.400 --> 0:02:07.760 lot of factors, it's not just one thing. Also, one 0:02:07.760 --> 0:02:11.239 way that folks will describe RAM versus storage is the 0:02:11.520 --> 0:02:15.440 kind of think of it like human short term memory 0:02:16.000 --> 0:02:19.160 versus long term memory. We use short term memory to 0:02:19.200 --> 0:02:22.480 handle something that's going on in the moment, such as 0:02:22.680 --> 0:02:25.079 let's say you meet someone for the first time, and 0:02:25.120 --> 0:02:28.440 they introduce themselves and they give you their name, so 0:02:28.560 --> 0:02:32.160 you use their name as you talk to them. We 0:02:32.280 --> 0:02:36.480 then commit important stuff to long term memory so that 0:02:36.520 --> 0:02:38.560 we can pull from that should we ever need to, 0:02:39.639 --> 0:02:42.200 like remembering that person's name when you see them at 0:02:42.200 --> 0:02:44.480 a function three years later. Then you don't want to 0:02:44.480 --> 0:02:46.919 look like a total jerk. By the way, I am 0:02:47.000 --> 0:02:50.040 really bad at long term memory. I'm not great at 0:02:50.040 --> 0:02:52.280 short term either. As it turns out, I kind of 0:02:52.320 --> 0:02:55.080 live in the moment. It's like the world is just 0:02:55.240 --> 0:02:57.919 constantly new and amazing to me. That's the way I 0:02:58.200 --> 0:03:00.519 prefer to think of it, rather than I him really 0:03:00.560 --> 0:03:04.360 bad at remembering people's names. But flash memory typically behaves 0:03:04.360 --> 0:03:07.560 more like a hard drive than RAM does. It's a 0:03:07.600 --> 0:03:10.840 way to store information for more of a long term solution. 0:03:11.120 --> 0:03:16.119 Flash drives are also known as solid state storage devices UH. 0:03:16.160 --> 0:03:19.560 They use an all electronic method to store data, as 0:03:19.560 --> 0:03:23.079 opposed to traditional hard drives, which have moving parts like 0:03:23.440 --> 0:03:29.079 platters and read right heads. Also, flash drives are non 0:03:29.360 --> 0:03:33.200 volatile forms of storage. That means that the data stored 0:03:33.280 --> 0:03:36.040 on a flash drive is going to stay there even 0:03:36.040 --> 0:03:39.040 if the computer that the drive is is connected to 0:03:39.560 --> 0:03:44.960 has been switched off. Stuff in RAM is volatile, so 0:03:45.440 --> 0:03:49.840 information stored in RAM is volatile. Memory that are volatile data. 0:03:49.920 --> 0:03:52.760 That means that information will go by by when you 0:03:52.800 --> 0:03:56.840 power your computer down. RAM requires power to continue to 0:03:56.920 --> 0:04:01.000 store information. That's not the case with flash storage. Or 0:04:01.000 --> 0:04:03.920 flash memory. Like a traditional hard drive, a flash drive 0:04:03.960 --> 0:04:08.360 will jealously cling onto that precious data. It just does 0:04:08.400 --> 0:04:11.480 so in a different way from traditional hard drives. All right, 0:04:11.520 --> 0:04:15.160 So let's do a quick rundown of how traditional hard 0:04:15.280 --> 0:04:18.520 drives work so that we can make this distinction. Now, 0:04:18.520 --> 0:04:21.279 I mentioned that a traditional hard drive has a platter 0:04:21.800 --> 0:04:26.000 and a read right head, so you can kind of 0:04:26.000 --> 0:04:29.280 think of it similar to a turntable or record player 0:04:29.480 --> 0:04:33.320 and vinyl records. Only imagine that your turntable is able 0:04:33.360 --> 0:04:35.680 to not just play music on a record, it can 0:04:35.720 --> 0:04:40.080 also record music to a blank record. Now, with vinyl records, 0:04:40.400 --> 0:04:43.760 we record information in grooves, and a stylist or needle 0:04:43.880 --> 0:04:47.599 travels through that groove, and the physical vibrations the grooves 0:04:47.600 --> 0:04:52.240 transferred to that stylus get transformed into an electric signal 0:04:52.440 --> 0:04:55.320 thanks to a tiny electro magnet that then can be 0:04:55.360 --> 0:04:58.320 amplified and sent to speakers, and then we get playback. 0:04:58.920 --> 0:05:03.040 With traditional hard drive, we're not talking about physical grooves. Instead, 0:05:03.080 --> 0:05:05.719 we're using the read right head, which is able to 0:05:05.760 --> 0:05:10.359 generate and detect magnetic fields, so it can align magnetic 0:05:10.480 --> 0:05:13.440 particles that are on the hard disk platter, and those 0:05:13.440 --> 0:05:17.640 particles based on their alignment, can represent zeros and ones, 0:05:18.000 --> 0:05:21.800 you know, bits, the basic language of computers. This, by 0:05:21.839 --> 0:05:23.880 the way, is why you may have heard that you 0:05:23.880 --> 0:05:28.080 should keep powerful magnets away from computers. If that computer 0:05:28.160 --> 0:05:32.239 relies on any type of magnetic storage, a powerful magnet 0:05:32.320 --> 0:05:35.800 could change the alignment of the particles on that platter, 0:05:36.360 --> 0:05:39.200 and that would destroy the data stored on it. You 0:05:39.240 --> 0:05:41.159 could do that on purpose too, in an effort to 0:05:41.160 --> 0:05:44.440 make an old hard drive unreadable, you know, to conceal 0:05:44.560 --> 0:05:48.600 whatever had been stored on the drive. We call this degassing, 0:05:48.720 --> 0:05:51.279 and uh, it's an important step. If you were to 0:05:51.320 --> 0:05:55.520 ever like retire a computer and you want to maybe 0:05:55.600 --> 0:05:58.320 donate it, or sell it or or give it away, 0:05:59.240 --> 0:06:01.279 chances are you want to make sure that anything that 0:06:01.400 --> 0:06:05.480 you had stored on that computer is well and truly gone. 0:06:05.920 --> 0:06:08.680 You don't want it to resurface at some point. It 0:06:08.760 --> 0:06:11.760 might have some sensitive information on there, So that's one 0:06:11.800 --> 0:06:15.200 reason you might want to decoss an old computer. But 0:06:15.320 --> 0:06:18.839 flash drives don't use magnetism to store data, So you 0:06:18.839 --> 0:06:21.440 could bring a powerful magnet near a solid state drive 0:06:21.560 --> 0:06:24.279 and you would not change a single bit of data 0:06:24.360 --> 0:06:28.160 that's stored on that device. So a flash or solid 0:06:28.200 --> 0:06:33.239 state drive isn't susceptible to the gossing. That's good and bad. 0:06:33.760 --> 0:06:35.280 It's bad only if you're trying to come up with 0:06:35.320 --> 0:06:39.000 a way to prevent someone from retrieving data that was 0:06:39.040 --> 0:06:41.080 once stored on that flash drive. You would have to 0:06:41.080 --> 0:06:44.920 take a different approach in order to do that. Now, 0:06:44.960 --> 0:06:47.800 the listener who left this request and my apologies but 0:06:47.960 --> 0:06:50.320 I don't actually have your name, mentioned that he was 0:06:50.400 --> 0:06:53.520 familiar with flash from ages back and referred to I 0:06:53.720 --> 0:06:57.880 PROM Now I'm assuming he means e E p R 0:06:57.960 --> 0:07:00.200 O M, but he could have meant E E p 0:07:00.480 --> 0:07:03.800 R O M will cover both. So E E p 0:07:04.080 --> 0:07:09.120 r O M stands for electronically eraseable programmable read only memory, 0:07:09.440 --> 0:07:13.160 and it is kind of a forerunner to flash. It's 0:07:13.200 --> 0:07:18.160 sort of the foundation that flash would be built upon, 0:07:18.280 --> 0:07:22.880 although the two are distinct. So let's talk about read 0:07:22.920 --> 0:07:27.520 only memory for a second because it's that's also important. Now, 0:07:27.680 --> 0:07:32.080 I already mentioned RAM, that's random access memory. RAM is 0:07:32.160 --> 0:07:35.280 volatile and it is rewriteable, meaning you can read or 0:07:35.360 --> 0:07:37.760 overwrite data stored in RAM as much as you like. 0:07:38.480 --> 0:07:43.000 Read Only memory or ROM is different, as the name indicates, 0:07:43.440 --> 0:07:48.400 you usually can only read data from a ROM storage 0:07:48.520 --> 0:07:52.600 source like a WRAM micro chip, but you aren't typically 0:07:52.680 --> 0:07:56.880 able to write new data to a ROM. With computers, 0:07:56.920 --> 0:08:00.760 we usually find very important basic level process is stored 0:08:00.760 --> 0:08:03.760 in ROMs, such as the boot sequence for a computer, 0:08:03.920 --> 0:08:06.640 so that your machine goes through all the necessary steps 0:08:06.960 --> 0:08:10.280 to swing into working order. You wouldn't want to overwrite 0:08:10.360 --> 0:08:13.400 that stuff. These are the most basic instructions needed to 0:08:13.560 --> 0:08:16.720 make the machine work. If you're in the main or 0:08:16.880 --> 0:08:21.240 multi arcade machine emulator scene, you might think of ROMs 0:08:21.280 --> 0:08:24.360 as the code for a specific arcade game. In the 0:08:24.400 --> 0:08:29.280 old days of arcades, manufacturers would program games on actual microchips. 0:08:29.760 --> 0:08:32.640 The game was never meant to change, and so programming 0:08:32.679 --> 0:08:35.439 them on rom's made perfect sense. So if you were 0:08:35.440 --> 0:08:38.000 to open up one of those classic arcade machines, you 0:08:38.040 --> 0:08:41.720 would find circuit boards holding various chips, and that, in 0:08:41.800 --> 0:08:44.880 fact would be the game. It's not from a disk 0:08:45.080 --> 0:08:47.480 or anything like that, unless you're talking about a game 0:08:47.520 --> 0:08:51.080 like Dragons Layer, which in fact used laser desk technology. 0:08:51.120 --> 0:08:54.120 But that's beside the point, and those games were stored 0:08:54.240 --> 0:08:58.800 on read only memory. However, e E PROM E PROM 0:08:58.880 --> 0:09:03.679 also includes the allotronically erasable programmable part. Right, So clearly 0:09:04.040 --> 0:09:08.520 I PROM is not exactly like traditional ROM. It is 0:09:08.880 --> 0:09:14.040 user modifiable. Users can erase and reprogram individual bytes of 0:09:14.120 --> 0:09:17.959 data stored on I PROM. This in itself was an 0:09:18.000 --> 0:09:22.599 evolution of single E E PROM E P R O 0:09:23.040 --> 0:09:27.840 M that was just eraseable programmable read only memory and listener. 0:09:27.880 --> 0:09:31.080 If this is what you were referring to, my apologies, Uh, 0:09:31.120 --> 0:09:33.600 it means that you go further back than I anticipated. 0:09:34.080 --> 0:09:38.240 So uh, E PROM actually was another form of PROM 0:09:38.360 --> 0:09:42.000 that's programmable read only memory. You might wonder what's the 0:09:42.000 --> 0:09:44.920 difference between E PROM with a single E and e 0:09:45.080 --> 0:09:47.680 PROM with a double E, and it really is that 0:09:47.840 --> 0:09:53.240 electronically eraseable part. So with the old e PROM chips 0:09:53.280 --> 0:09:57.040 one E, you could technically erase data that was stored 0:09:57.080 --> 0:09:59.920 on that chip. However, to do so, you first had 0:10:00.080 --> 0:10:02.640 to expose the chip to ultra violet light for a 0:10:02.640 --> 0:10:07.240 good long while, like an hour. So imagine having to 0:10:07.280 --> 0:10:10.000 wait an hour in order to erase data that was 0:10:10.080 --> 0:10:13.200 stored on a chip so that you could write over 0:10:13.240 --> 0:10:16.520 it again. Obviously, that would not be viable for your 0:10:16.559 --> 0:10:19.880 average user. Data on a double E e PROM, on 0:10:19.960 --> 0:10:23.040 the other hand, could be erased by applying a slightly 0:10:23.120 --> 0:10:27.160 higher than normal electrical voltage to the chip. Now, as 0:10:27.200 --> 0:10:30.079 you might imagine, that's way less work than exposing a 0:10:30.160 --> 0:10:33.240 chip to ultra violet light, and it made e PROM 0:10:33.760 --> 0:10:39.520 storage viable for specific applications, not yet to the point 0:10:39.559 --> 0:10:43.120 of a solid state drive. Now, before I jump into 0:10:43.160 --> 0:10:46.199 what makes flash work, remember flash is kind of an 0:10:46.240 --> 0:10:50.200 evolution of e PROM. But let's let's talk about the 0:10:50.320 --> 0:10:53.680 history of flash. So i PROM dates back a few decades, 0:10:54.160 --> 0:10:56.480 and flash we can actually trace back to the mid 0:10:56.600 --> 0:11:01.800 nineteen eighties. Dr Fugio Massuoka, who was working for Tashiba, 0:11:01.960 --> 0:11:05.920 developed flash memory. Masuoka said that the name flash was 0:11:05.960 --> 0:11:10.400 actually suggested by a colleague, Mr. Shoji are Zumi, because 0:11:10.679 --> 0:11:14.360 Razumi felt that the process of a racing store data 0:11:14.440 --> 0:11:17.760 off the the flash method was very similar to an 0:11:17.760 --> 0:11:21.520 old school cameras flash. Now, I suspect that some of 0:11:21.559 --> 0:11:23.880 you all out there might not have had that much 0:11:23.920 --> 0:11:28.280 experience with flash cameras because everyone's using their phones, and 0:11:28.400 --> 0:11:31.400 I mean some people have like the little led flash 0:11:31.600 --> 0:11:33.760 on their phones. But it's totally different from the old 0:11:33.760 --> 0:11:37.760 flash cameras, which used capacitors to generate a very quick, 0:11:37.960 --> 0:11:40.160 very bright flash of light when you were taking a 0:11:40.160 --> 0:11:44.199 picture in low light situations. And flash cameras used to 0:11:44.240 --> 0:11:46.240 be huge, and of course they still are being used 0:11:46.240 --> 0:11:48.920 in some settings, like professionals of course still use them, 0:11:49.400 --> 0:11:51.520 but a lot of I think a lot of the 0:11:51.520 --> 0:11:54.640 average people out there probably have had limited access to 0:11:54.720 --> 0:11:57.880 them if they are below a certain age. I'm of 0:11:57.920 --> 0:12:00.960 an age where I remember flash being like just standard 0:12:01.000 --> 0:12:03.920 on cameras, like you really needed it or else. Any 0:12:03.960 --> 0:12:07.800 picture you took indoors was not going to come out properly. Anyway, 0:12:08.080 --> 0:12:11.600 the actual methodology for storing data on a flash drive 0:12:12.040 --> 0:12:15.120 was really clever. I'll talk about that more after we 0:12:15.200 --> 0:12:25.679 come back from this break. Okay, let's talk about how 0:12:25.960 --> 0:12:30.320 flash data is stored in the first place. Imagine you 0:12:30.440 --> 0:12:35.120 have a grid, so you've got columns and you've got rows. 0:12:36.120 --> 0:12:40.880 Each box in this grid, each cell within that grid 0:12:41.240 --> 0:12:45.719 has two transistors located at each of the intersections around it. 0:12:46.400 --> 0:12:49.120 One of those transistors is what we would call a 0:12:49.240 --> 0:12:53.040 floating gate transistor, which holds a charge inside it. The 0:12:53.120 --> 0:12:57.320 other is a metal oxide silicon or moss transistor and 0:12:57.400 --> 0:13:01.160 serves as the control gate. Uh now, I guess I'm 0:13:01.160 --> 0:13:04.560 gonna need to talk about gates. As we're using floating 0:13:04.559 --> 0:13:06.880 gate and control gate. That doesn't really mean anything unless 0:13:06.920 --> 0:13:10.240 you dive a little further in. So gates are really 0:13:10.320 --> 0:13:13.960 that's shorthand for logic gates, and this serves as the 0:13:14.000 --> 0:13:19.280 foundation for any circuitry system uh, specifically digital systems. So 0:13:19.360 --> 0:13:21.880 with a logic gate, you've got a circuit that at 0:13:21.920 --> 0:13:25.360 least has at least one input, and it can have 0:13:25.440 --> 0:13:27.880 more than one, but has at least one, and it 0:13:27.960 --> 0:13:32.280 has only a single output. And what is being input 0:13:32.400 --> 0:13:36.400 and output in this case, well, we're talking electric charges. Uh. 0:13:36.400 --> 0:13:40.000 These circuits provide specific functions which we designate with names 0:13:40.000 --> 0:13:46.960 like and or not nor nand and so on. Those 0:13:47.040 --> 0:13:50.559 names tell us how the gates behave and the output 0:13:50.600 --> 0:13:53.760 that they will produce based upon the type of input 0:13:54.240 --> 0:13:59.040 coming into the gate. For example, a simple and gate 0:13:59.480 --> 0:14:02.920 might have two inputs and will refer to these inputs 0:14:03.000 --> 0:14:05.920 as input A and input B, and it has a 0:14:05.960 --> 0:14:09.560 single output. Remember all gates have a single output we'll 0:14:09.559 --> 0:14:14.200 call the output X. There are four possible scenarios with 0:14:14.280 --> 0:14:18.400 this gate, which we will represent using binary data or bits. 0:14:18.480 --> 0:14:21.840 That's that is, zeros and ones. So instead of talking 0:14:21.840 --> 0:14:24.920 about electric charges. We're gonna talk about feeding zeros and 0:14:25.040 --> 0:14:27.680 ones to a logic gate through its inputs and what 0:14:27.960 --> 0:14:31.680 is generated as an output. Now you've got your and 0:14:32.000 --> 0:14:35.360 logic gate, and let's say that you feed zeros to 0:14:35.520 --> 0:14:39.880 both input A and input B. Well, and AND gate 0:14:40.080 --> 0:14:44.440 will then produce a zero as the output. So output 0:14:44.720 --> 0:14:47.760 X will generate a zero. Now let's say that you 0:14:47.840 --> 0:14:50.680 feed a zero to input A and a one to 0:14:50.840 --> 0:14:55.040 input B to your hand gate. Well, the X output 0:14:55.160 --> 0:14:58.560 will still be zero. In fact, the only way that 0:14:58.680 --> 0:15:02.880 the X will equal one is if both A and 0:15:03.040 --> 0:15:07.240 B inputs are ones. That's why it's called an and gate. 0:15:07.600 --> 0:15:11.520 The gate produces a one if all inputs going into 0:15:11.520 --> 0:15:14.560 the gate are also ones. And remember like we're talking 0:15:14.560 --> 0:15:18.040 about a simple example here where we have two inputs, 0:15:18.040 --> 0:15:20.160 but you could have more than two inputs going into 0:15:20.200 --> 0:15:22.960 a single gate, but it would have to be all 0:15:23.200 --> 0:15:25.840 ones going into that gate for the gate to produce 0:15:26.000 --> 0:15:29.560 a one. On the other side, with flash drives, we're 0:15:29.560 --> 0:15:34.240 talking about NOR or nand architectures, So a NOR gate 0:15:34.320 --> 0:15:37.520 will only produce a one if all inputs going into 0:15:37.600 --> 0:15:41.640 the gate are at zero. So if input A zero 0:15:41.800 --> 0:15:45.680 input via zero, then x will equal one. But with 0:15:45.720 --> 0:15:48.400 any other combination, like if you have all ones or 0:15:48.400 --> 0:15:51.040 a combination of zeros and ones going in as input, 0:15:51.520 --> 0:15:55.280 the output is going to be a zero. A nand 0:15:55.360 --> 0:15:59.520 gate is a not and gate. This will produce a 0:15:59.560 --> 0:16:03.640 one out put in every single case, except when all 0:16:03.720 --> 0:16:07.080 inputs are ones. So if you've got two or more 0:16:07.200 --> 0:16:09.520 zeros going into a nand gate, you're gonna get a 0:16:09.560 --> 0:16:12.000 one coming out. If you get a combination of ones 0:16:12.040 --> 0:16:14.320 and zeros, you're gonna get a one coming out. If 0:16:14.320 --> 0:16:18.080 all the inputs are ones, you get a zero coming out. Now, 0:16:18.760 --> 0:16:22.000 these are the functions gates can serve, and you can 0:16:22.040 --> 0:16:25.200 actually program stuff by creating all these different logic gates 0:16:25.240 --> 0:16:31.680 in a various series in order to produce particular you know, outcomes. 0:16:31.720 --> 0:16:34.400 But let's talk about the gates themselves. So we're talking 0:16:34.440 --> 0:16:38.720 about transistors here. The transistors and electric circuits can serve 0:16:38.800 --> 0:16:42.000 as a type of switch, either allowing data to pass 0:16:42.040 --> 0:16:46.680 through or not. On one side of the transistor, you 0:16:46.760 --> 0:16:49.600 have the source that is the place where input is 0:16:49.640 --> 0:16:52.520 coming from, and on the other side of the gate, 0:16:52.600 --> 0:16:55.640 you have the drain that's the place where the output 0:16:55.840 --> 0:16:59.640 is going to. With a standard moss fat transistor. A 0:16:59.720 --> 0:17:04.640 moss FET stands for metal oxide semiconductor field effect transistor. 0:17:05.280 --> 0:17:08.879 You would open the gate or you know, turn the 0:17:08.920 --> 0:17:13.000 switch on by placing a charge on the gates electrode. 0:17:13.440 --> 0:17:17.560 That would turn the semiconductor transistor into a conductor and 0:17:17.600 --> 0:17:21.040 allow electricity to flow through. Removing the charge from that 0:17:21.119 --> 0:17:25.800 electrode makes the semiconductor transistor behave like an insulator. That's 0:17:25.840 --> 0:17:29.280 the big deal with transistors. They can, depending on the situation, 0:17:29.720 --> 0:17:33.200 act either as a conductor or insulator. They can either 0:17:33.280 --> 0:17:37.719 allow a charge to move through or prevent it. All right, Now, 0:17:37.800 --> 0:17:41.600 let's talk about a floating gate transistor that has an 0:17:41.600 --> 0:17:45.680 extra piece to it. The floating gate is electrically isolated 0:17:45.920 --> 0:17:49.840 from the rest of the transistor. That isolation is key 0:17:50.000 --> 0:17:52.560 because it means once you store a charge in a 0:17:52.600 --> 0:17:56.520 floating gate, that charge will stay there. And that's because 0:17:56.560 --> 0:17:59.720 the floating gate isn't connected to a drain where the 0:18:00.040 --> 0:18:03.720 charge could otherwise go. This gets a bit tricky to 0:18:03.800 --> 0:18:06.399 explain without visual aids, but I'll give it a go. 0:18:06.880 --> 0:18:09.040 All right, So with a flash drive, we've got your 0:18:09.119 --> 0:18:12.080 control gate, and we've got your floating gate, and an 0:18:12.080 --> 0:18:16.080 intersection in this grid of rows and columns. The rows 0:18:16.160 --> 0:18:19.160 of the grid are the word line, and the word 0:18:19.240 --> 0:18:22.639 line goes through the control gate. With that link, the 0:18:22.720 --> 0:18:25.399 cell and flash memory holds the value of one, so 0:18:25.480 --> 0:18:29.160 by default, all the cells in flash memory are set 0:18:29.320 --> 0:18:32.760 to one, not to zero. To change any cell to 0:18:32.840 --> 0:18:35.000 the value of zero, you actually have to put in 0:18:35.040 --> 0:18:39.119 some work. So the rows are the word line. What 0:18:39.280 --> 0:18:43.439 then are the columns, Well, that's called the bitline. The 0:18:43.520 --> 0:18:46.800 bitline can carry a charge to the floating gate by 0:18:46.800 --> 0:18:50.320 pushing the charge through at a slightly higher voltage than 0:18:50.400 --> 0:18:53.280 what is used for the control gate. That's enough for 0:18:53.359 --> 0:18:57.600 electrons to bridge the gap of the otherwise isolated floating gate, 0:18:57.960 --> 0:19:00.520 and the floating gate will then hold a negative of charge. 0:19:00.600 --> 0:19:04.800 Because electrons are negatively charged sub atomic particles, and this 0:19:04.840 --> 0:19:09.399 process is called the Fouler nord Heim tunneling process. The 0:19:09.440 --> 0:19:12.000 collection of electrons in the floating gate then becomes kind 0:19:12.000 --> 0:19:15.760 of a negatively charged force field between the floating gate 0:19:15.800 --> 0:19:19.040 and the control gate. A cell sensor monitors how much 0:19:19.119 --> 0:19:21.960 charge passes through the floating gate, and if the flow 0:19:22.520 --> 0:19:25.400 is above a certain threshold, the value of the cell 0:19:25.520 --> 0:19:28.960 is interpreted as a one. If the value is below 0:19:29.280 --> 0:19:32.879 this threshold, the value within the cell is considered to 0:19:32.880 --> 0:19:35.520 be zero. So another way to think about it is 0:19:35.560 --> 0:19:38.960 that if the cell conducts a current, it's representing one. 0:19:39.280 --> 0:19:42.120 If it is acting more like an insulator, it's representing 0:19:42.440 --> 0:19:47.119 a zero. To return the cell value to one, you 0:19:47.200 --> 0:19:51.919 have to apply a higher voltage electric field to the cell. 0:19:52.359 --> 0:19:55.760 And really this process typically targets sections of the flash 0:19:55.800 --> 0:19:59.320 memory called blocks, particularly for the type of flash memory 0:19:59.320 --> 0:20:04.840 that we who's frequently um and sometimes you might even 0:20:04.920 --> 0:20:09.080 have to target the entire flash chip itself and boiled down. 0:20:09.200 --> 0:20:12.640 By controlling the voltage to the control and floating gates 0:20:12.640 --> 0:20:15.520 of the transistors on the solid state drive, you can 0:20:15.560 --> 0:20:20.640 create the zeros that represent the data. Remember it's by 0:20:20.680 --> 0:20:24.320 default it's set at one, So really creating zeros is 0:20:24.320 --> 0:20:27.479 what is writing data to that. Otherwise you just have, 0:20:28.160 --> 0:20:32.159 you know, a block of ones. So erasing flash memory 0:20:32.200 --> 0:20:34.520 really just means turning all the cells within the memory 0:20:34.520 --> 0:20:37.040 to one, and writing to flash memory really just turning 0:20:37.280 --> 0:20:40.600 means turning selective cells to zero. So let's say you're 0:20:40.600 --> 0:20:44.359 starting off with a bite of blank flash memory. Uh, 0:20:44.400 --> 0:20:47.840 that would be eight ones. So a bite is eight bits, right, 0:20:47.880 --> 0:20:51.000 and we've established that a blank cell is a cell 0:20:51.040 --> 0:20:54.320 that's holding a one within it. Let's say you want 0:20:54.359 --> 0:20:57.639 to write a bite that is actually zero followed by 0:20:57.720 --> 0:21:02.600 seven ones. You could theoretically keep writing to that same bite. 0:21:02.680 --> 0:21:06.240 You could change you could reprogram that byte by changing 0:21:06.359 --> 0:21:10.760 other ones in that series to zeros over time. You 0:21:10.800 --> 0:21:13.760 could not, however, change in these zeros back to ones 0:21:14.400 --> 0:21:18.160 without erasing the entire byte, really, without erasing the entire 0:21:18.200 --> 0:21:21.440 block that the bite is on. So you could write 0:21:21.520 --> 0:21:24.600 data in the form of zero one zero one, zero 0:21:24.680 --> 0:21:28.440 one zero one, but you could not then go back 0:21:28.480 --> 0:21:32.359 to zero followed by seven ones without first erasing everything 0:21:32.400 --> 0:21:36.280 and starting over. It gets a little confusing. Don't worry, 0:21:36.480 --> 0:21:39.360 it will get more confusing. I should also mention there's 0:21:39.400 --> 0:21:42.879 also flash RAM. But that's the type of volatile memory, 0:21:42.920 --> 0:21:45.720 meaning if it does lose power, then any information stored 0:21:45.760 --> 0:21:48.720 within that memory is lost. This is the type of 0:21:48.760 --> 0:21:51.880 memory found in things like car radio systems, where you've 0:21:51.960 --> 0:21:56.520 maybe stored preset radio stations and such. So you might think, 0:21:56.560 --> 0:21:59.600 but my radio stations stay on even after I'm you know, 0:21:59.640 --> 0:22:02.359 turn off the car and I get out and do whatever. 0:22:02.880 --> 0:22:05.120 But when your car is off, that system is still 0:22:05.160 --> 0:22:07.920 drawing a very tiny amount of power from your car's 0:22:07.960 --> 0:22:11.520 battery in order to maintain those settings. However, if your 0:22:11.600 --> 0:22:15.040 vehicle were to totally lose power, like let's say you 0:22:15.080 --> 0:22:18.440 had the battery completely removed, then you would lose that 0:22:18.560 --> 0:22:22.280 data and you would have to reset all your favorite stations. Okay, 0:22:23.000 --> 0:22:25.199 when we come back, we'll get into a little bit 0:22:25.200 --> 0:22:29.680 more detail about NAND versus NOR architectures, because flash comes 0:22:29.720 --> 0:22:33.159 in both, and we'll talk a bit more about how 0:22:33.520 --> 0:22:38.679 flash is organized by architecture. Uh trust me, it actually 0:22:38.760 --> 0:22:42.040 is really interesting. It does get a bit complicated, don't worry. 0:22:42.520 --> 0:22:44.679 I'm here with you every step of the way. But 0:22:44.800 --> 0:22:55.800 first let's take a quick break. Okay. I mentioned earlier 0:22:55.960 --> 0:23:00.399 that flash typically comes in NAND and NOR architect ictures, 0:23:00.800 --> 0:23:02.960 and the NAND architecture is the one most of us 0:23:02.960 --> 0:23:05.440 have experience with. It's the type of memory used for 0:23:05.920 --> 0:23:10.639 SD cards, USB flash drives, and computer solid state drives. 0:23:11.359 --> 0:23:15.680 NOR is usually used for storing digital configuration information. Uh 0:23:15.840 --> 0:23:20.640 nand flash has transistors in grid wired in series. NOR 0:23:20.800 --> 0:23:24.639 flash has its transistors or cells wired in parallel. That 0:23:24.920 --> 0:23:30.840 architecture does matter because with NOR you can actually program 0:23:30.840 --> 0:23:32.919 at the bite level. You can write and rewrite at 0:23:32.920 --> 0:23:35.679 the bite level. When nand you have to do it 0:23:35.760 --> 0:23:37.960 at a much larger level, which we'll get to in 0:23:37.960 --> 0:23:41.760 a second. And we're gonna stick with nand because again 0:23:41.800 --> 0:23:44.960 that's the type most of us interact with regularly. The 0:23:45.119 --> 0:23:49.120 organization of a nand flash drive goes with cell, which 0:23:49.160 --> 0:23:52.159 is your individual unit in which you know you're storing 0:23:52.200 --> 0:23:56.119 either a zero or a one one by default. Next, 0:23:56.480 --> 0:24:00.120 you have strings, and as that name suggests, a string 0:24:00.280 --> 0:24:02.840 is a series of cells that are connected to one another, 0:24:03.240 --> 0:24:06.159 where the source of one cell connects to the drain 0:24:06.400 --> 0:24:10.480 of the next cell. One level up from strings, and 0:24:10.560 --> 0:24:14.440 you have pages. So a page is a collection of strings. 0:24:15.119 --> 0:24:18.840 A collection of pages makes up a block, and a 0:24:18.920 --> 0:24:24.560 collection of blocks connected through the same bitline makes a plane. Finally, 0:24:24.640 --> 0:24:27.639 you've got the flash dye, which consists of one of 0:24:27.880 --> 0:24:31.119 or more planes, plus all the components that allow the 0:24:31.240 --> 0:24:36.360 drive to write, erase, and read data in those cells. Now, 0:24:36.400 --> 0:24:39.280