1 00:00:00,000 --> 00:00:05,200 Every computer needs RAM to function. But did you know that pretty much all the RAM we use these days 2 00:00:05,200 --> 00:00:08,880 uses some clever tricks to run much faster than it otherwise would? 3 00:00:09,520 --> 00:00:15,280 Even older RAM, like this, DDR3 I'm holding, uses these techniques. 4 00:00:15,280 --> 00:00:20,240 In fact, it's right in the name. DDR stands for double data rate, which means, 5 00:00:20,240 --> 00:00:25,600 just what it sounds like it means, it can move data twice as quickly as single data rate memory, 6 00:00:25,600 --> 00:00:32,080 which hasn't been in our computers for very long. The original DDR actually came out way back in 2000, 7 00:00:32,080 --> 00:00:35,600 not to be confused with the other DDR which came out in 1998. 8 00:00:35,600 --> 00:00:39,520 Unfortunately, I don't have a stick of the original DDR to show you, 9 00:00:39,520 --> 00:00:46,160 but I can show you a bit about how it works. So this is an example of a simple clock signal 10 00:00:46,160 --> 00:00:49,760 that your computer uses to keep components inside synced up. 11 00:00:50,400 --> 00:00:54,160 Conventionally, one piece of data is sent per cycle, 12 00:00:54,160 --> 00:01:00,560 or for each one of these humps. But you see how each cycle has a rising and a falling edge? 13 00:01:00,560 --> 00:01:04,560 Well, DDR sends data on both the rising and the falling edges, 14 00:01:04,560 --> 00:01:10,640 which works because your memory modules can detect at what point the internal clock is in its cycle. 15 00:01:10,640 --> 00:01:17,600 But hold on a second, this would only be double the data rate over a super old school single data rate RAM. 16 00:01:17,600 --> 00:01:22,400 So how are we getting generational improvements like DDR2, 3, and 4, 17 00:01:22,400 --> 00:01:25,760 which continue to increase the data rate by a factor of 2, 18 00:01:25,760 --> 00:01:32,080 each time? It turns out that there are actually two clocks involved in what make DDR RAM work, 19 00:01:32,080 --> 00:01:35,520 the external bus that connects your RAM to the rest of the system, 20 00:01:35,520 --> 00:01:40,720 and an internal memory clock. For DDR2, the internal clock was kept the same, 21 00:01:40,720 --> 00:01:48,240 but the external bus clock was doubled. This means that the external bus can carry twice as much data per unit of time. 22 00:01:48,240 --> 00:01:52,720 To take advantage of this, the internal memory array where the data is actually stored 23 00:01:52,720 --> 00:01:57,120 doubles the number of bits sent at one time to the external memory bus. 24 00:01:57,120 --> 00:02:02,560 This process is also called prefetching, and it's responsible for why DDR2 is faster than DDR, 25 00:02:02,560 --> 00:02:08,720 and why DDR3 is faster than DDR2. The external bus's faster clock can then carry the extra data, 26 00:02:08,720 --> 00:02:13,920 and boom, you've got faster memory. Advances in manufacturing that keeps signal integrity high 27 00:02:13,920 --> 00:02:18,560 have allowed newer versions of DDR to operate at these higher speeds without a hitch. 28 00:02:18,560 --> 00:02:22,640 It should be noted, however, that DDR4 works slightly differently 29 00:02:22,640 --> 00:02:25,920 in that memory arrays are divided into bank groups, 30 00:02:25,920 --> 00:02:29,200 which means that prefetches can be pulled from different parts of the RAM 31 00:02:29,200 --> 00:02:32,960 at the same time, leading to higher speeds than DDR3. 32 00:02:32,960 --> 00:02:36,800 Boosting the external clock is also part of how newer versions of DDR 33 00:02:36,800 --> 00:02:40,640 can run at faster clock speeds while drawing less power. 34 00:02:40,640 --> 00:02:45,600 Because the internal memory array runs at speeds slower than the external bus, 35 00:02:45,600 --> 00:02:48,640 and sends more prefetch data per cycle, 36 00:02:48,640 --> 00:02:54,000 it keeps power requirements from getting too high, which, when combined with smaller die sizes, 37 00:02:54,000 --> 00:02:58,080 means new DDR generations don't need as much voltage. 38 00:02:58,080 --> 00:03:01,280 Of course, unlike many other generational improvements, 39 00:03:01,280 --> 00:03:06,400 one thing that newer versions of DDR do not feature is backwards compatibility. 40 00:03:06,400 --> 00:03:12,960 This is a stick of current gen DDR4, and you'll notice that when I hold it up next to this stick of DDR3, 41 00:03:12,960 --> 00:03:20,080 that the notches are in different places. That means that these two sticks cannot be used in the same motherboard. 42 00:03:20,080 --> 00:03:26,080 It's made this way on purpose, since the different generations of DDR have different electrical and signaling requirements. 43 00:03:26,080 --> 00:03:30,720 That, or it's just a plot to make all of us buy new memory every couple of years. 44 00:03:30,720 --> 00:03:35,040 Either way, I'll cough up whatever they want as long as it has RGB. 45 00:03:35,040 --> 00:03:41,040 So thanks for watching guys, if you like this video, hit like, 46 00:03:41,040 --> 00:03:46,560 hit subscribe, and hit us up in the comments section with your suggestions for topics that we should cover in the future.