Request an intro to memory timing

[Patchworkblue]

I always see people writing about memory, with 4 numbers behind, separated by dashes. I believe the first one is CAS latency, what's the rest? Thanks.

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[bum_jcrules]

A-B-C-D

A= tCAS = Time Delay (t) Column Access Strobe (CAS) (Pulse Duration in cycles)

B = tRCD = Time Delay (t) RAS Active to CAS Active

C = tRP = Time Delay (t) RAS Precharge

D = tRAS = Row Access Strobe (Pulse Duration in cycles)

The first latency, tCAS, is time delay specified before the memory controller will send out the next instruction. It is the wait time for the CAS pulse signal to finish. If it or any other delay is too short there will be corrupted output data at the end of the read.

tRCD is the delay between the cycle sets.

tRP is the charge given to refersh/deactivate the row.

tRAS is the total active to de-activate time.


Some people post the command rate timing. You see it as CMD 1T or CMD 2T. It is the delay before the first command is issued after the chip select or the memory selection.


If you need further explanations feel free to ask.




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[ytoledano]

When the memory timings are listed like with my Corsair Twinx 256A-3200LL, the timings are 2-3-2-6 T1. Which one is the CAS, RCD...?

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[bum_jcrules]

The way they are normally listed is in the order I listed it above.

A-B-C-D CMD

tCAS, tRCD, tRP, tRAS, CMD

2-2-3-6 1T, 2.5-3-3-7 2T, etc.

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[Patchworkblue]

So, is it better to have lower numbers in all categories? As in, lower values equal higher performance, while higher values equal higher stability?

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[bum_jcrules]

For simplicity's sake yes.

However not all settings should be at the lowest number possible. As for those listed above, yes that is a correct assesment.





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[jennylow]

Thanks for the information on CAS.

My Asus PNP800 has DRAM timing setup in the BIOS, but I
can't figure out a few items.

The five BIOS items to setup are:

CAS Latency [2.0, 2.5, 3.0] - tCAS A

RAS to CAS [4, 3, 2] - tRCD B

RAS Precharge [4, 3, 2] - tRP C

DRAM Precharge Delay [8, 7, 6, 5]

DRAM Burst Length [4, 8]

Which of the last two is "Row Access Strobe"?

What do the last two BIOS settings mean?

Thanks,

Jen

 

[bum_jcrules]

This is what I hate about some motherboard settings.

DRAM Precharge Delay is tRAS. Dumb name for it but that is what it is.

Burst length can be set to either 4 or 8 quad words per burst. The higher the number the higher your peak bandwidth. Set it to 8.



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