SMP with a P3 800 and P3 750

[GFORCE100]

Hi guys,

I have this dilema. I have dual P3 800's. I decided to overclock them to 900MHz on my SMP board. However only one of the CPU's will do 900MHz stable in intensive apps at this speed without increasing it's Vcore. Now this has been bugging me and I don't want to start taping pins really.

I also have a P3 750. All CPU's are Slot 1. I have three Pentium III's altogether, all retail boxed versions and all CBO stepping. Now, I was thinking. Can I put the P3 750 in place of one of my P3 800's in my SMP board and run it? Is that possible? The only difference is that one of the CPU#s has a multiplier of 7.5x and the other 8x. I feel this is possible but would like to double check?

Alternatively I'll be seeking to either replace one P3 800 or the P3 750 with someone else's retail boxed P3 (800Mhz) that can do 900Mhz at the default voltage. I thought of perhaps offering my P3 750 and throwing in a new Enermax 330W PSU which I have left from reviewing.

May someone provide feedback on this? For now I would love to put the P3 750 in along side my P3 800 and have Windows 2000 work on both overclocked CPU's. Then it would be 840MHz and 900MHz working along side it each other.

Thanks for your input.

 

[bacillus]

I always thought that both cpus had to be the same speed & stepping so I would also be interested to see if anyone could provide concrete evidence to the contrary!

 

[Bignate603]

I think the processors have to be the same but i'm not sure.

 

[GFORCE100]

Yes that's what I'm trying to find out. If not then someone who will trade with me and who lives in the UK prerebly. One of the P3 800's seems to like more than 1.7V which just means it's more thirsty, not neccessarily a bad overclocker.

 

[LarryJoe]

I am no expert on SMP, but I just don't get why you want to do what you are trying to do. First, I always thought both CPU's had to be the same speed or identical to SMP. If this is not true, what is the big deal with a 900/800 vs. 900/840? Is this all about the additional 40mhz the 750 will give you? If so, not worth the effort of even bending down to remove the 800 that won't do 900, IMO.

LJ

 

[GFORCE100]

You can't have 800/900 because of the locked multipliers.

 

[LarryJoe]

I am saying keep both 800's in there and just overclock one if that is possible.

 

[GFORCE100]

I can't overclock one. I wish there was such an option, would come in very handy.

 

[Hanpan]

They don't have to be the same stepping or speed however they have to run at the same speed. I'm about 95% sure. For example you could run a cbo 750@1000 with a cco 1000 mhz chip. However whichever chip is in the first socket set the voltage. I think you can even match fc-pga with adapter and slot one. It is that they run the same speed taht is importatn. I don;t think it would hurt to try. Might try asking pm about this one thouhg.

 

[Phil21]

You could underclock the 800 to have it work at 750 and you'd be fine (disclaimer: 9 times out of 10). You cannot use different speed CPU's in SMP. Period. They both must run the same speed, and they both will have the same FSB/multiplyer. I remember running socket7(ha!) P133's dual, with one P200 underclocked. ALso make sure both CPU's use the same voltage, I just ran into that without thinking with two PII 450's. one was an SECC chip, and the other was SECC2. It seems the SECC2's use more voltage, and it severely cooked the SECC CPU. Luckily I saw the machine locking up randomly on boots and felt (ok burnt the hell out of) the chip with my hand.

So, as long as both CPU's are the same voltage, same FSB, and same multiplyer you'll be fine. There is no way to have say a 500mthz chip work with a 1000 mhtz chip.

peace,

-Phil

 

[GFORCE100]

I've tried it. To cut a long story short I think it's a synchronization issue. Will lockup if I ran a CPU benchmark. Booted fine though, no beeps.

The thing is you cannot underclock one processor, and nor may you change the multiplier.

 

[KpocAlypse]

If ya want go to 2cpu. There is no doubt someone there who will be able to answer you question

 

[Sir Fredrick]

Obviously, a lot of the people who posted in this thread do not know much about SMP. To meet Intel specs, both processors MUST be the same speed and the same stepping. That is not to say that mismatched speed/stepping processors won't work, it's just to say that there's no guarantee.

Since the only way you can adjust the speed of a PIII is through FSB, a 750 and an 800 can't possibly ever run at the same speed (both processors share a FSB). A 750 and an 800 could work together, but there's no guarantee, and even if they work together they might not be stable. When it comes to running an SMP system, there is already a greater chance of instability, so I would not recommend any extreme amounts of overclocking anyway.

 

[AndyHui]

Sir Frederick: not exactly. Intel has explicitly stated that for SMP, processors must at a minimum be of the same speed, and same class of processor. There are provisions for mixed stepping SMP systems; the mixed stepping matrix for SMP is located in the Specification Update.

Intel allows for, but does not support SMP with mixed steppings and even with different cache sizes.