WEBVTT 00:00:00.080 --> 00:00:06.480 every computer needs RAM to function but did you know that pretty much all the 00:00:04.160 --> 00:00:09.599 RAM we use these days uses some clever tricks to run much faster than it 00:00:08.240 --> 00:00:12.400 otherwise would even older RAM like 00:00:11.519 --> 00:00:17.600 this ddr3 i'm holding uses these techniques 00:00:15.360 --> 00:00:22.160 in fact it's right in the name ddr stands for double data rate which means 00:00:20.320 --> 00:00:26.400 just what it sounds like it means it can move data twice as quickly as single 00:00:24.560 --> 00:00:32.079 data rate memory which hasn't been in our computers for very long the original 00:00:28.400 --> 00:00:34.079 ddr actually came out way back in 2000 00:00:32.079 --> 00:00:38.960 not to be confused with the other ddr which came out in 1998. unfortunately i 00:00:36.480 --> 00:00:42.399 don't have a stick of the original ddr to show you but i can show you a bit 00:00:40.879 --> 00:00:48.000 about how it works so this is an example of a simple clock 00:00:45.280 --> 00:00:53.199 signal that your computer uses to keep components inside synced up 00:00:50.399 --> 00:00:59.280 conventionally one piece of data is sent per cycle or for each one of these humps 00:00:56.559 --> 00:01:04.559 but you see how each cycle has a rising and a falling edge well ddr sends data 00:01:02.079 --> 00:01:08.799 on both the rising and the falling edges which works because your memory modules 00:01:06.479 --> 00:01:13.280 can detect at what point the internal clock is in its cycle but hold on a 00:01:11.200 --> 00:01:18.240 second this would only be double the data rate over a super old school 00:01:15.760 --> 00:01:23.759 single data rate RAM so how are we getting generational improvements like 00:01:20.159 --> 00:01:26.080 ddr2 3 and 4 which continue to increase 00:01:23.759 --> 00:01:30.479 the data rate by a factor of two each time it turns out that there are 00:01:28.320 --> 00:01:34.799 actually two clocks involved in what make ddr RAM work the external bus that 00:01:33.360 --> 00:01:40.079 connects your RAM to the rest of the system and an internal memory clock for 00:01:37.759 --> 00:01:45.040 ddr2 the internal clock was kept the same but the external bus clock was 00:01:42.799 --> 00:01:49.680 doubled this means that the external bus can carry twice as much data per unit of 00:01:47.600 --> 00:01:53.840 time to take advantage of this the internal memory array where the data is 00:01:51.680 --> 00:01:58.560 actually stored doubles the number of bits sent at one time to the external 00:01:56.000 --> 00:02:03.840 memory bus this process is also called prefetching and it's responsible for why 00:02:00.640 --> 00:02:06.159 ddr2 is faster than ddr and why ddr3 is 00:02:03.840 --> 00:02:10.959 faster than ddr2 the external bus's faster clock can then carry the extra 00:02:08.319 --> 00:02:14.879 data and boom you've got faster memory advances in manufacturing that keeps 00:02:12.800 --> 00:02:18.800 signal integrity high have allowed newer versions of ddr to operate at these 00:02:16.800 --> 00:02:23.680 higher speeds without a hitch it should be noted however that ddr4 works 00:02:21.200 --> 00:02:27.360 slightly differently in that memory arrays are divided into bank groups 00:02:25.840 --> 00:02:31.360 which means that prefetches can be pulled from different parts of the RAM 00:02:29.200 --> 00:02:36.239 at the same time leading to higher speeds than ddr3 boosting the external 00:02:33.840 --> 00:02:41.360 clock is also part of how newer versions of ddr can run at faster clock speeds 00:02:38.319 --> 00:02:43.360 while drawing less power because the 00:02:41.360 --> 00:02:49.120 internal memory array runs at speeds slower than the external bus and sends 00:02:46.480 --> 00:02:53.360 more prefetch data per cycle it keeps power requirements from getting too high 00:02:51.280 --> 00:02:59.200 which when combined with smaller die sizes means new ddr generations don't 00:02:56.080 --> 00:03:01.519 need as much voltage of course unlike 00:02:59.200 --> 00:03:06.879 many other generational improvements one thing that newer versions of ddr do not 00:03:04.000 --> 00:03:10.800 feature is backwards compatibility this is a stick of current gen ddr4 and 00:03:09.120 --> 00:03:16.080 you'll notice that when i hold it up next to this stick of ddr3 that the 00:03:13.360 --> 00:03:20.400 notches are in different places that means that these two sticks cannot be 00:03:18.239 --> 00:03:23.599 used in the same motherboard it's made this way on purpose since the different 00:03:22.000 --> 00:03:28.319 generations of ddr have different electrical and signaling requirements 00:03:26.080 --> 00:03:32.640 that or it's just a plot to make all of us buy new memory every couple years 00:03:30.720 --> 00:03:37.519 either way i'll cough up whatever they want as long as it has RGB big thanks to MSI 00:03:36.000 --> 00:03:43.599 for sponsoring this video 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