Detailed RAM spec help

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HollywoodNZ

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Feb 19, 2015
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So before I get into it, this is as good as homework so I'm really looking for discussion or maybe a pointer to material to read rather than just an answer :)

So I have an upcoming hardware lab session based on RAM and I am trying to prepare for it.
In the lab I need to identify

  • Memory standard
    Interface type
    Module operating speed
    Bus or interface speed
    Bandwidth
    Latency

I have got most of it (I think) but I'd really appreciate if someone could look it over for me :) So here's what I've got CPU-Z Screen Grab


  • Memory Standard: PC10667
    Interface: DDR3
    Module Operating Speed: 665MHz (standard is 667?)
    Bus or Interface Speed: I'm stuck on how to find this
    Bandwidth: 10.6GB/s, 1325MB/s. I found this in a chart of standards and speeds but would love to know exactly how to find it
    Latency: 9 Clocks (9Hz? if anyone knows the equation to work it out it's be great)

Any input or advice would be greatly appreciated

Thanks in advance, HollywoodNZ




 
Solution
B
OK.

Memory standard, should be PC3-10667. The 3 denotes it is DDR3 memory type based.

Module operating speed, is two times the memory clock frequency. Because DDR (Double Data Rate) memory operates two times per memory clock cycle. CPU-z shows the memory clock frequency as 665.1 MHz, so the memory will operate at two times 665.1 MHz = 1330.2 MHz.

Bus or interface speed(?). Memory usually operates on a 64 bit wide data bus. The speed of that bus is the operating frequency of the memory module, which is 1330.2 MHz in this case.

Bandwidth is memory operating frequency times data bus width divided by 8. Here it is 1330.2 MHz x 64 bit / 8 = 10641.6 MB/s ~ 10 GB/s.

CAS Latency is the Column Address Strobe which is the delay in...
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brispuss

Splendid
Dec 27, 2014
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26,490
OK.

Memory standard, should be PC3-10667. The 3 denotes it is DDR3 memory type based.

Module operating speed, is two times the memory clock frequency. Because DDR (Double Data Rate) memory operates two times per memory clock cycle. CPU-z shows the memory clock frequency as 665.1 MHz, so the memory will operate at two times 665.1 MHz = 1330.2 MHz.

Bus or interface speed(?). Memory usually operates on a 64 bit wide data bus. The speed of that bus is the operating frequency of the memory module, which is 1330.2 MHz in this case.

Bandwidth is memory operating frequency times data bus width divided by 8. Here it is 1330.2 MHz x 64 bit / 8 = 10641.6 MB/s ~ 10 GB/s.

CAS Latency is the Column Address Strobe which is the delay in clock cycles to select memory cell columns. To convert that latency to nano-seconds (ns), formula is 2000 x CAS / memory operating frequency (MHz) = 2000 x 9 / 1330.2 = 13.5 ns, in this case.
 
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Solution
H

HollywoodNZ

Reputable
Feb 19, 2015
9
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4,510
Hey, thanks for your reply!

So I've got most of that now thanks, but just to confirm some stuff in regards to latency. When a module has an advertised latency of CL15 would this mean it's latency is 15 ns? How do they get the number that they advertise?
Also is it always 2000 or does it vary depending on the module?

Again thank you for all your help :)

Cheers

 
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B

brispuss

Splendid
Dec 27, 2014
2,607
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CAS latency, by default, means the number of clock cycles. So if a module is advertised as having a CL of 15, then that module will have a CAS latency of 15 clock cycles. And the equivalent period in nano seconds has to be calculated using the formula as above.

CAS latency is determined by the characteristics of memory chips used to make memory modules. The memory chip manufacturer supplies the details of the memory chip parameters, including CL, to memory module manufacturers (and usually also made publicly available) as an aid in determining the performance of memory modules.

The constant "2000" is for all of the DDR range of memory modules from DDR through to DDR4.

This constant changes to 1000 for SDR (Single Data Rate) memory modules ONLY.
 
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