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saluy

OC'ing RAM

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So I was talking to a friend that knows computers and he says 'so have you set up your latency with your CPU' and I was like 'wahh'

So if any of you atomicons have any ideas on:

1) what he is talking about and

2) how to work out what the formula is to set it up.

 

cheers,

Saluy

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i can see your using a 2500k cpu which is pretty easy to calculate. I'll try and explain it simply.

 

the motherboard has a base clock speed of 100mhz. the cpu and the ram use multipliers to adjust this base frequency to the one they want to run at.

example. i5 2500k = 3.3ghz = 33x100mhz = 33 multi.

 

your ram is exactly the same. 1600mhz ram = 16x100 = 16 multi.

1866mhz = 18.66 multi

2133mhz = 21.33 multi

 

once you chose the right speed, usually 1600 for most common ram, you can also configure the ram latency. usually it does a good job to figure this out by itself and you should only really change it if you know what it should be set to.

this is the time between instructions basically, lower latency is faster ram.

don't confuse this with improved performance though, yes it is improved, but usually by something like 0.1% or 0.5% if anything, and is only noticable under specific conditions, such as benchmarking.

 

I think your mate is either a bit confused himself, or just giving out poor advice.

hope this was useful.

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There's two main components when it comes to memory. Latency and clock rate. Basically memory latency consists of five main timings, commonly written in the form:

 

X-X-X-X XT

 

Where X just a natural number value. In order, these latencies are CL, RCD, RP, RAS and the 'command rate'. Do we care what they're called? Not really.

 

The formulas I use when adjusting memory are:

 

CL = RP

RAS = CL + RCD + 4

Command rate = 1 (usually, otherwise 2)

 

These are based on experience rather than any theoretical studies, but they're generally reliable. I've also found that lowering RCD achieves the best gains.

 

So basically in the BIOS you should be able to adjust these values. Lowering them improves performance - this is known as 'tightening' the latencies. On the other hand, if you raise them, you are 'loosening' the latencies. The general rule of thumb is to increase the clock rate of the memory (as you would a processor) until the memory becomes unstable, and then try loosening the latencies to see if you can achieve a higher clock rate. If not, revert back to the last stable clock and try tightening the latencies instead.

 

Of course, I'm assuming you've at least overclocked a CPU before, and are familiar with using a BIOS and changing clock rates.

Edited by .:Cyb3rGlitch:.

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Of course, I'm assuming you've at least overclocked a CPU before, and are familiar with using a BIOS and changing clock rates.

Looks like he got the simple version and the advanced version now :)

I did not make the assumption he knows anything about overclocking or bios lol.

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i can see your using a 2500k cpu which is pretty easy to calculate. I'll try and explain it simply.

 

the motherboard has a base clock speed of 100mhz. the cpu and the ram use multipliers to adjust this base frequency to the one they want to run at.

example. i5 2500k = 3.3ghz = 33x100mhz = 33 multi.

 

your ram is exactly the same. 1600mhz ram = 16x100 = 16 multi.

1866mhz = 18.66 multi

2133mhz = 21.33 multi

 

once you chose the right speed, usually 1600 for most common ram, you can also configure the ram latency. usually it does a good job to figure this out by itself and you should only really change it if you know what it should be set to.

this is the time between instructions basically, lower latency is faster ram.

don't confuse this with improved performance though, yes it is improved, but usually by something like 0.1% or 0.5% if anything, and is only noticable under specific conditions, such as benchmarking.

 

I think your mate is either a bit confused himself, or just giving out poor advice.

hope this was useful.

We are both quite young and into computers so thank you

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Finding a good balance between latency and speed is the go, pretty much any generic DDR3 should do 1800 cas 8-8-8-24 or something (for example) with up to 1.6v

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Finding a good balance between latency and speed is the go, pretty much any generic DDR3 should do 1800 cas 8-8-8-24 or something (for example) with up to 1.6v

that would be nice but unless my corsair vengance 1600 c9 sticks just dont like the p67-ud4 mb 1866 10 to 11 is barely stable letalone 8 even at 1600 it can only do 8-9-8 with 1.5v tried up to 1.68v it just didnt help last i tried but that may have been trying to get it to post at 2133mhz

 

edit been playing with it again this morning the tops are

1600mhz 8-9-8-24 1.5v 1.05vtt

1940mhz 9-11-9-28 1.56v 1.2vtt

not sure that the later is any faster or if its actually slower yet

Edited by Dasa

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Vtt is very low, tried up to 1.3 or 1.35??

there seems to be some conflicting info about what the max safe vtt is for sandy is most seem to say make sure its under 1.15-1.2v

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Ah I see, interesting.. So is sandy inheirtly bad for memory ocing?

I'm not sure if 1366 needs much vtt for high clocked ram if using a divider to keep bclk low

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most people dont need more than 1.15vtt for overclocking ram to ~1866-2133 with sandy mostly depends on the ram as to what level is reached i think

seems i need more vtt than most though as always there is some luck involved or maybe i just need to play with the sub timings some more but i have seen plenty of others stuck at low limits with ddr3 it seems some sticks are not made with any oc room

 

found this earlier today

cheap 30nm 1.35v lp sticks from samsung that can oc rather well for the price still not great timings though

http://www.xtremesystems.org/forums/showth...968#post5013968

Edited by Dasa

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