PII 955 OC

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Posting this in here as it doesn't seem to be getting noticed. Mod can lock/delete the one in 8 Pack's section.


New to OC'ing and recently got my 955 to 3.8Ghz on 1.425v. Prime stable at <50. (as far as I can tell)

The above is with everything set to "normal" + x19 multi.

I can get prime to run for a few mins @ 4Ghz on 1.5v but then bluescreen. Can I assume from this that I'm close to stable?

Would appreciate some help on getting a solid 4Ghz, is it time to start changing more settings? People recommend upping the NB for best performance.

I attempted to change FSB and NB slightly whilst leaving everything else the same. The former gave bluescreen and NB changes cause "fatal errors" on some cores in prime.

Thanks
 
If you raise the HT reference clock (there is no FSB) then you also overclock the Hypertransport bus, which must at all times and without question by as close to 2000MHz as you can get, preferably under if you can't get it bang on.

Secondly overclocking the CPU-NB requires an increase in voltage, this will also heat up the CPU which potentially hurts your CPU overclock.

To get your CPU stable at 4GHz should only be a matter of CPU voltage and cooling. However, if your temperatures are breaching 55C then you're at the limit and further voltage will not help stability.

My suggestion would be to try and tighten your RAM timings and clock your CPU-NB to 2400MHz at 3.8GHz CPU speed. I've found it's hard to run your memory at 1600 speed or greater with Deneb chips.

Stretch goal: CPU-NB at 2600MHz with 7-7-7-21 timings on your RAM.
 
JonSmith said:
If you raise the HT reference clock (there is no FSB) then you also overclock the Hypertransport bus, which must at all times and without question by as close to 2000MHz as you can get, preferably under if you can't get it bang on.

Secondly overclocking the CPU-NB requires an increase in voltage, this will also heat up the CPU which potentially hurts your CPU overclock.

To get your CPU stable at 4GHz should only be a matter of CPU voltage and cooling. However, if your temperatures are breaching 55C then you're at the limit and further voltage will not help stability.

My suggestion would be to try and tighten your RAM timings and clock your CPU-NB to 2400MHz at 3.8GHz CPU speed. I've found it's hard to run your memory at 1600 speed or greater with Deneb chips.

Stretch goal: CPU-NB at 2600MHz with 7-7-7-21 timings on your RAM.
Click to expand...

Thanks for the input. The variation in naming confuses me. Heat doesn't look like it's an issue at the minute. Are you saying the only thing that will make me stable at 4Ghz is upping the vcore?

The HT reference clock you speak of is the same one that effects CPU freq?

I increased the CPU-NB to 2400 but that's when I encountered core errors. If I'm looking at the correct option, the voltage is set to 1.3 as standard. Which option do I increase NB voltage or NB VID are the only two I can see. (The CPU-NB is shown under Memory>NB Freq in CPU Z?) Everything else is set to "normal" with the exception of the multiplier and the cpu voltage. Including ram which is auto at 9-9-9-24, 1333mhz @ 1.5v. HT bus remains at 2000 exactly.

Will the ram be affecting stability if I change the CPU-NB freq? Or do I simply need more volts on the CPU-NB?
 
This should help. NB VID is the voltage for the CPU NB. This is what i was running for benchmarking for superpi. CPU voltage missing off the bottom which was 1.55V.
cpu-1_zpsf2a8afec.jpg


This has all been dialled back to these settings for everyday use:
CPU - 242 x15.5 - 3751MHz @ 1.45V
CPU NB - 242 x11 - 2662MHz @ 1.3V
HT LINK - 242 x8 - 1936MHz
RAM - 242 x6.66 - 1612MHz - 9-9-8-18-20-1T @ 1.65V (8GB kingston & 4GB corsair with SPD timings at 1600 of 9-9-9-27-36)
 
Thanks very much Kei, is that also on a 955? Funnily enough I figured CPU NB Vid out this afternoon and have set the CPU-NB multi to x13 (2600mhz), had to bump the voltage to 1.225 but so far prime has been fine, still at 3.8Ghz. Temps no hotter either, although it has been a little cooler outside.

Would I see much improvement from pushing further? 4Ghz might be possible on 1.55v but is that safe?


Side note: Whilst searching on-line, someone explicitly stated not to alter the CPU NB Vid, which is incorrect.
 
1.55V is the maximum (recommended) safe, but I'd expect you'd hit the heat wall before you reached that level. Once the core temperature rises past 55C, don't bother increasing the voltage further as it will not help. Up until that point, go for it.

I wouldn't recommend clocking further because the CPU-NB bump will give you about 5% more performance, coupled with clocking your RAM for a couple of percent makes up for it. You probably won't be able to clock your CPU-NB at 4GHz for thermal reasons.
 
JonSmith said:
1.55V is the maximum (recommended) safe, but I'd expect you'd hit the heat wall before you reached that level. Once the core temperature rises past 55C, don't bother increasing the voltage further as it will not help. Up until that point, go for it.

I wouldn't recommend clocking further because the CPU-NB bump will give you about 5% more performance, coupled with clocking your RAM for a couple of percent makes up for it. You probably won't be able to clock your CPU-NB at 4GHz for thermal reasons.
Click to expand...

Do you have a source for the limits? I checked the AMD website but it states 1.5v. Would you advise I stick to 2600 on the CPU-NB as well?

I suppose it's best if I stay well within the limits than push it right to the edge of safety anyway, especially if the gains are so small. Seen around 2 FPS improvement in Hitman, although the improvement may well be more in other applications.
 
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I've been running a c3 955 BE stable at 3.8 GHz, 1.392v with a 2200MHz Nb on stock v
My chip would clock stable to 4.1GHz but ran too hot for long term use @1.44v. Things may be different now I have my H100 though...
 
AT Orchard said:
Thanks very much Kei, is that also on a 955? Funnily enough I figured CPU NB Vid out this afternoon and have set the CPU-NB multi to x13 (2600mhz), had to bump the voltage to 1.225 but so far prime has been fine, still at 3.8Ghz. Temps no hotter either, although it has been a little cooler outside.

Would I see much improvement from pushing further? 4Ghz might be possible on 1.55v but is that safe?


Side note: Whilst searching on-line, someone explicitly stated not to alter the CPU NB Vid, which is incorrect.
Click to expand...
Yes that is a 955, but it is an older C2 stepping which needs more voltage to remain stable vs a C3. Mine is not very stable above 3.8GHz no matter how many volts I put through it, so I stick with 3.75. (mine is watercooled and was quite comfortable even at 1.6V, but i still wouldn't want to run that 24/7) The NB overclock makes all of the difference though.
 
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