What's safe to over clock on amd's? 138-145fsb?

[gtr]

I'm running a xp1700 and was curious if their is any bad outcomes if i overclock it at 138fsb "cpu". What is a safe number? Or is it best to leave it alone?

I'm currently running ddr266. If i run a ddr333 could the cpu be overclocked more with better results?

Also if over clock what voltage is good?

thanks in advance. Newbie in Over clocking and don't want to mess the chips up.

[Ape0r]

Just keep your temps under 60C and you'll be fine. I run my Athlon XP 1900+ at 139 FSB.

[jmichna]

Ditto on 139fsb... XP2100+ @1807mHz (139x13.0=XP2200+ speed)

Will soon unlock the CPU, then will play around with 166FSB/166mem bus (around 10.5 or 11.0 multiplier on the cpu).
jmichna

[Bigjakkstaffa]

Ive gone up to 155 before, but after a few months you'll notice graphical corruption - id say 140mhz FSB is a sensible limit

--Jakk

[gtr]

Thanks, As for memory bus it's only safe "error free" to up it to 166 Mhz is with ddr333 right?

[jmichna]

Originally posted by gtr
Thanks, As for memory bus it's only safe "error free" to up it to 166 Mhz is with ddr333 right?

"DDR2700"="ddr333"... both terms mean the same, and are for 166mHz speed, but good quality ram can be pushed significantly beyond the 166 limit. With my mobo at 139fsb, that pushes my mem bus to approx 175mHz (fsb x 1.25). Other folks tweak the mem timings and get much higher speeds, in the 180's and 190's.

DDR3200 (ddr400) would buy more "head room" but do you really think you will need it?
jmichna

[gtr]

Thanks I think i see now. When the fsb is turned up it actually increases the multiplier. This cause an increace with both pci bus and memory bus. However the memory bus could also be increased by setting the cas to 2 instead of 2.5 or something, correct?

[jmichna]

Originally posted by gtr
Thanks I think i see now. When the fsb is turned up it actually increases the multiplier. This cause an increace with both pci bus and memory bus. However the memory bus could also be increased by setting the cas to 2 instead of 2.5 or something, correct?

CAS has no effect on the mem bus speed, they are independent of one another. Having said that, CAS is (sort of) how fast the memory chips work internally. CAS stands for - I believe - "Column Addressing Strobe" and is analagous to the refresh rate of earlier mem chips. There are longer technically accurate descriptions in many articles, but I don't have them handy right now. CAS 2.0 is faster than 2.5 which is faster than 3.0. The mem bus speed is how fast the memory communicates with the rest of the pc.

If you want to try to run your mem bus as fast as possible, you then have to back down a bit on how aggressive you set your CAS timings. You have to try to find the optimum "sweet spot" between mem bus and CAS, that yields the higherst memory throughput. There are several programs people use to measure memory performance to do this. SiSoft Sandra is one popular one.

The various vendors sort and rate their memory as to how fast it will work for a given mem bus speed. For example, you can by Corsair DDR ram that will run at 166mHz at CAS 2.0, and you can buy Corsair DDR ram that will at 166mHz at CAS 2.5. You will pay a bit more for the CAS 2.0 flavor.

Most people seem to settle on trying to achieve the highest possible mem bus speed while keeping their memory timings at CAS 2.0 (or whatever the mem is rated at). Others have found it to their advantage to run as fast a mem bus as possible, slowing down CAS until they achieve stability.

I'm sure other folks here at Sysopt can give more technically accurate information.
jmichna

[bigblue]

jmichna makes some good arguements.
I'm no CAS expert, but I have achieved 166mhz FSB, ran a 3dMark2001SE, before chickening out and bringing her back out of the clouds. I run CAS3 PC133, but results vary depending on way too many factors. Things running on the PCI bus can crash everything if it can't handle the extra mhz. Different models of the same processor can make a difference in how stable it performs at high FSBs.

It's really on keeping your CPU cool, monitoring that temperature closely, and keeping things stable.