What is the speed of RAM today? CL – CAS Latency – Cas delay … For the pros may say something. Only … why the higher the speed of the RAM is higher than Cl? It seemed to me what should be the opposite.
Opening any DDR4, I did not find a dailure, for example, for DDR3 here http: / /www.icsi.com.tw/pdf/43tr16256a-85120al.pdf I read – 13 nanoseconds – i.e. about 66mnz, i.e. Sam memory 1866MN, and what is there 13 nanoseconds? Those. Is it a non-examination of 100 times slower? For DDR4, it also became incomprehensible to CL14 – a delay of 14 nanoseconds i.e. Are the same 66MNZ? Nevertheless, they promise full speed in the “bandwidth of 19200 MB / s” equal to 8 * 2400 MHz.
Do I understand correctly, CAS signal processing lasts 14 ns for CL14, and RAS-less nanoseconds?
It turns out that during one CAS-circulation it would be possible to make 100 Ras appeals (100 roughly, really 1866 / 71nnz = 26 but the higher the memory, the indicator above). And if we intentionally force the CPU in a secure mode to sort out the data from different CAS-prints (it is possible through the CR3 to the RAM, make fun to physically allow 256 pages, with addresses specifically with a 256MB interval, and run on reading 1gig plot with a step in 4096) then get speed Memory about 70mhz (14 ns)?
how much% CL-parameter reduces the speed of memory? As I understand it, the page size … 32-bit is 4GB, Paired Ras-Cas give a rough 16 bits. 2 at 16 degrees equal to 64k, i.e, entering the border of the memory of the memory 64kb (maybe real 256k-bytes) you have to switch the page. With a linen reading – every 64k linear read operations will have 1 time to switch spending … 0,1K per CAS (for 2400 CL14). Roughly 0.1%? And in reality we lose from 1% to 10% of the speed of memory for CL14? 2400 / 70MNZ = 34Cyclas or percentage of speed loss other?
What is the best 2400MNZ CL14 or 2666MNZ CL17? Somehow the figure 17 Well, source scares. CL17 (58mn) will give a slowdown from 1.2% to 12% compared with P3? 2666/58 = 46 cycles. UDP: DDR4 3200MNZ CL15 is the number of cycles of “idle” about 55, and it seems that this figure will grow …
Answer 1, Authority 100%
Do I understand correctly, the CAS signal processing lasts 14 ns for CL14, and RAS-less nanoseconds?
1) incorrectly, the delay is indicated in the treads of the RAM tires (14 clocks).
2) Mixed horses, people, the answer to the question – no, just the messenger of everything in a row in the question.
CAS – Time to open the column, RAS – time to “open” strings. Without opening the string, you will not read anything by opening the column – you can read the lines. those. Reading time = Cas + Ras (Rough very much I think it is clear that they are not separable).
It is difficult to measure the speed in the following 70MHZ values - it’s anything but not speed.
3) directly – does not reduce at all, it is not about the maximum channel speed, but about the time between the query and the answer. To achieve maximum speed – you need to either request large blocks or many (overhead will increase, but they are also included in the bandwidth of the channel).
What is the best 2400MNZ CL14 or 2666MNZ CL17? Somehow a number 17 Well, source scares.
4) It depends on what you need, the delays are less – in the first case, but nevertheless the speed will be equal to the second.
CL17 (58MNZ) will give a slowdown from 1.2% to 12% compared with P3? 2666/58 = 46 cycles. UDP: DDR4 3200MNZ CL15 is the number of cycles of “idle” about 55, and it seems this figure will grow …
These counts are above my forces.
CL17 means that if you send a request to RAM, then before the first you received byte, 17Tacts (+ TRCD) will be passed, further – faster, then each byte will be triggered by RAS.
2666MHz ~ 46ns + Ras to receive the first byte, further Ras for each subsequent.
At the same time, no one bothers you to make several requests.
Almost everything or everything written in this answer was in the comments.
Real speeds on real hardware will be far from the theoretical ones that we read from datasheets. The minimum latency is not always necessary, and high speed is not always important, choosing such things you need to understand the purpose of use precisely.