[Xtreme Barton]

ok i know its been mentioned alot of times but i cant make the difference between what people are saying.. one thing and the other..

what is cpc in merlins bios? what does it do when its off and on ?

how does this affect my cpu and ram ??

[fateshammer]

Originally Posted by Xtreme Barton

ok i know its been mentioned alot of times but i cant make the difference between what people are saying.. one thing and the other..

what is cpc in merlins bios? what does it do when its off and on ?

how does this affect my cpu and ram ??

Command Per Clock (CPC) also used to be known as Command Timing back in the days. Its about latency. Where 1T=1 clock cycle and 2T=2 clock cycles. Presently, CPC On=1T and CPC Off=2T. Obviously, 1T means tighter timings than 2T. The main issue about turning it off for many users seem to be the possibility of achieving higher FSB's when using 2x512Mb memory sticks, but at the expense of bandwidth efficiency. For a lot of users with 2x256Mb, its always CPC On. Of course, CPC Off isn't always beneficial to all with 2x512Mb rams. Some with 2x512 also get positive results with CPC On.

[DaWiper]

Isn't CPC all about if your memory sticks are singel or double sided?
Meaning, for best performance: singel=cpc on(1t), double=cpc off(2t)?

[red_dragon]

no no no, people use cpc off w/ 2x512 because nf2 has probs addressing 2x512 with 1T latency. even more trouble if your dimms are double sided. That's why people w/ 2x512 use CPC off...But I don't think it's worth it.

[Miguita]

Really? I don't think this applies to nForce2 in particular. I've had stability issues on my P4-system that is unlikely caused by anything but Command Rate (can't be changed in the BIOS). Besides I've read that the Command Rate is related to both module size, and, in particular, number of banks.

The following quote is found at
http://www.lostcircuits.com/advice/bios2/7b.shtml


"DRAM Command Rate is synonymous for address and commmand decode latency of the chipset. Briefly, behind this parameter is the selection of the proper physical bank within the entire memory space in any given system. Any DIMM can have two physical banks and only one bank can be accessed at any time. The choice of which bank is opened requires decoding of the address. In a scenario where only one single-sided DIMM is present in the system, the choice is the default since there are no other possibilities.
If a double-sided DIMM is used instead, the controller has to make an intelligent choice with respect to the issueing of the so-called chip select (CS) command to select the correct bank within which the information is stored. In case, there are two double-sided DIMMs in the system, there are four possible choices and only one is correct. Decoding a larger memory space will take more time and that is why most chipsets currently offer a variable CMD rate where the choices are 1T or 2T."

[Highlander]

Have to run CPC off with my OCZ and DFI setup, for some reason its just not stable, and thats with 2*256, single sided! The BW hit is a fair amount (~ 100mbs in memtests readout, which aint that accurate but i get the idea)
Thing is, the ram runs ok in the NF7 with cpc on... random!
Anway, me stop rambling, if you can run CPC on, gives much better performance.

[felinusz]

I ran CPC on with my 2 X 512 megabytes of OCZ PC3500 EB RAM, and Tictac's D10 4X4 Turbo CPC on, and I got it up to 240 MHz stably, although I needed a little moe voltage then most do with this RAM. I couldn't find an option for CPC in this BIOS (Unless it's still listed "CPU interface" - in which case I simply didn't bother to turn it of and test) , so I didn't get to test my changed limits with 2T.

So, I would imagine that whether CPC causes problems or not is related to the individual RAM somehow as well.