1 00:00:06,330 --> 00:00:07,650 - [Instructor] Let's quickly discuss 2 00:00:07,650 --> 00:00:11,160 data transfer rates for RAM. 3 00:00:11,160 --> 00:00:11,993 Now on the left here, 4 00:00:11,993 --> 00:00:16,970 we have a CPU and the CPU relies on cache memory internally 5 00:00:18,090 --> 00:00:22,710 to store the most commonly used instruction sets. 6 00:00:22,710 --> 00:00:25,710 But the cache memory is very limited. 7 00:00:25,710 --> 00:00:27,930 So, all the other data 8 00:00:27,930 --> 00:00:32,930 needs to be stored, for this current session, on RAM. 9 00:00:34,260 --> 00:00:37,530 Because there's so much data during a computer session, 10 00:00:37,530 --> 00:00:40,560 we need to make sure that the RAM is fast 11 00:00:40,560 --> 00:00:43,413 and can transfer a lot of data per seconds. 12 00:00:44,670 --> 00:00:46,080 How do we find that out? 13 00:00:46,080 --> 00:00:49,080 Well, let's give an example here 14 00:00:49,080 --> 00:00:54,080 and we'll say that this is a DDR4 memory module 15 00:00:56,040 --> 00:01:01,040 and the type is DDR4-2133. 16 00:01:01,530 --> 00:01:06,530 Now some people will refer to this as 2,133 megahertz 17 00:01:07,710 --> 00:01:12,710 but really what this means is 2,133 mega transfers. 18 00:01:15,060 --> 00:01:20,060 It can do 2,133 mega transfers 19 00:01:20,130 --> 00:01:23,850 or millions of transfers per second. 20 00:01:23,850 --> 00:01:25,320 Now, how do we figure out 21 00:01:25,320 --> 00:01:29,280 exactly what the data transfer rate is 22 00:01:29,280 --> 00:01:31,530 from the memory to the CPU? 23 00:01:31,530 --> 00:01:33,117 Well, we have to think a little bit here 24 00:01:33,117 --> 00:01:34,950 and we have to say okay, 25 00:01:34,950 --> 00:01:38,523 the RAM needs to communicate with the CPU. 26 00:01:39,420 --> 00:01:44,220 And it does that by way of the address bus. 27 00:01:44,220 --> 00:01:49,220 And that is a 64-bit bus, 64-bits. 28 00:01:51,630 --> 00:01:52,890 Now, what does that mean? 29 00:01:52,890 --> 00:01:57,360 Let's go down to our little calculation area down here. 30 00:01:57,360 --> 00:02:02,360 64-bits means that there's actually 64 circuits 31 00:02:04,320 --> 00:02:09,320 and we can send 64-bits of data simultaneously per cycle. 32 00:02:09,630 --> 00:02:12,090 Now, if we want to figure out the amount of actual data 33 00:02:12,090 --> 00:02:15,390 that we can transfer, we want to calculate for bytes. 34 00:02:15,390 --> 00:02:19,833 So 64-bits actually equals eight bytes. 35 00:02:20,730 --> 00:02:23,943 Because there's eight bits per byte. 36 00:02:25,500 --> 00:02:28,323 So 64-bits equals eight bytes. 37 00:02:29,880 --> 00:02:34,770 Every cycle we're sending eight bytes of data 38 00:02:34,770 --> 00:02:36,300 and there's a ton of cycles. 39 00:02:36,300 --> 00:02:37,230 How many? 40 00:02:37,230 --> 00:02:41,940 2,133 mega cycles basically. 41 00:02:41,940 --> 00:02:44,700 So what are we talking about here? 42 00:02:44,700 --> 00:02:48,750 Well, we wanna find out the maximum data transfer rate 43 00:02:48,750 --> 00:02:51,660 and solve for bytes. 44 00:02:51,660 --> 00:02:55,920 So we could do that by taking this number here, 45 00:02:55,920 --> 00:03:00,270 2133 and multiplying by eight, 46 00:03:00,270 --> 00:03:04,650 by the amount of bytes that are sent per cycle, that's it. 47 00:03:04,650 --> 00:03:09,540 So let's bring over our trusty calculator and do the math. 48 00:03:09,540 --> 00:03:13,277 If we do 2133x8, we'll get 17064 49 00:03:19,110 --> 00:03:23,820 but really it's a little higher than that, it's 17,066. 50 00:03:23,820 --> 00:03:27,810 Let me redo the calculation a little bit more accurately. 51 00:03:27,810 --> 00:03:32,810 2133.33, because this is really a repeating decimal. 52 00:03:33,090 --> 00:03:37,650 So it's 2133.33 and the threes keep going. 53 00:03:37,650 --> 00:03:41,280 It's okay to just stop at two decimal points though. 54 00:03:41,280 --> 00:03:46,280 So we'd say 2133.33x8 and that'll give us 17,066. 55 00:03:49,320 --> 00:03:54,263 And really the answer would be 0.6666 repeating decimal. 56 00:03:54,263 --> 00:03:58,623 But this is good enough for me, 17,066. 57 00:03:59,610 --> 00:04:01,860 But how much are we talking about here? 58 00:04:01,860 --> 00:04:05,940 Remember that we're talking about mega transfers. 59 00:04:05,940 --> 00:04:10,940 So really it's 17066 megabytes per second. 60 00:04:12,390 --> 00:04:15,030 So the total data transfer rate 61 00:04:15,030 --> 00:04:20,030 is going to equal 17,066 megabytes per second. 62 00:04:23,550 --> 00:04:27,270 That's how much data we can transfer back and forth 63 00:04:27,270 --> 00:04:29,610 between the RAM and the memory controller 64 00:04:29,610 --> 00:04:31,172 that's part of the CPU. 65 00:04:31,172 --> 00:04:34,950 17,066 megabytes per second. 66 00:04:34,950 --> 00:04:38,520 That's what this particular RAM can do. 67 00:04:38,520 --> 00:04:43,050 Other types of RAM with higher mega transfers per second 68 00:04:43,050 --> 00:04:46,020 will send more megabytes per second. 69 00:04:46,020 --> 00:04:50,970 But basically all you're doing is using the same equation. 70 00:04:50,970 --> 00:04:55,970 You'll say mega transfers per second times eight 71 00:04:56,190 --> 00:04:57,930 and solve for bytes. 72 00:04:57,930 --> 00:05:02,880 So that'll equal the amount of megabytes per second 73 00:05:02,880 --> 00:05:04,920 and that's it, that'll be your equation 74 00:05:04,920 --> 00:05:09,690 regardless of what DDR4 or five or whatever you're using. 75 00:05:09,690 --> 00:05:14,340 Now, this name here, DDR4-2133, 76 00:05:14,340 --> 00:05:18,210 that's the DDR4 standard 77 00:05:18,210 --> 00:05:23,210 but it will correspond to a module name quite often. 78 00:05:25,380 --> 00:05:28,890 And that name will be based off of 79 00:05:28,890 --> 00:05:31,080 the amount of megabytes per second. 80 00:05:31,080 --> 00:05:35,133 So for example, this module standard is DDR4-2133 81 00:05:37,290 --> 00:05:40,593 but the module name would be PC4-17000. 82 00:05:45,330 --> 00:05:50,330 And you might see it read as 17,066 also. 83 00:05:50,520 --> 00:05:54,630 That would be the actual module name for this RAM. 84 00:05:54,630 --> 00:05:58,260 So there's a little data transfer rate calculation 85 00:05:58,260 --> 00:05:59,223 for a DDR4.