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Dual Pentium with different speed

I like to know if is it possible to have a mainboard to run two Pentium III with different speed. I have a Pentium III 866MHZ and Pentium III 600MHZ. I intend to build a workstation with the above. Please advise on what motherboard is reccommended if the above combination is possible? Also,any resources on the internet which I can find out more about the above.thks in advance.
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Well, I'll try to comment here. As far as I know, the board will NOT run at two different speeds. However, even though it's not a recommended idea (by manufacturers, that it), it's perfectly possible to build a dual mobo box with different speed CPU on it. Stick the 600 in the socket with a lower number (CPU1) and then the 800 (CPU2) in the other. This way both run at slower speed. If your board has jumpers to specify speeds then you can propably even increase the speed for the 600, that overclocking -;).

I've done in on Tyan Tiger 230T. www.tyan.com. Works fine. I've also done it on other makes. As to how easy it is, depends. I wouldn't venture recommend a board, though.

Overclockers.com has a few good articles about it. www.dualcpu.com had an arcticle but don't quote me on that 'cause they seem offline at the moment.

Hope this is helpful to some degree,


Surferman's idea would work if the CPU clock multipliers weren't locked.

The CPUs cannot run at different speeds due to timing issues between the CPUs and the chipset.

Meanwhile, with the cost of an 800Mhz P3 chip at $85, I recommend you just get a new chip to match your existing 800.

For good dualie motherboards, check out motherboards by SuperMicro at  www.supermicro.com

I have owned several and they are excellent for reliability.

If your budget allows and you prefer, you can always get a prebuilt dual CPU capable system from your favorite manufacturer (IBM, HP, Dell, etc) with one 800Mhz CPU installed and add the one you already have.
Good point on timing issue, magarity. Still, it's my understanding that the board design permitting, the multiplier locking works the way that it won't allow people running the CPU's FASTER than the specified speed. However, nothing forbids you running you CPU SLOWER than it's capable of. As I said, a lot depends on the board. Some boards have everything locked, some allow, and I quote from ABIT's site "greater freedom of choice..." As for myself, that's the part I like. -:)

Here's a link to an article from Intel's site, about how to use PIII CPU:


Even they admit that "...Operation with different speed processors is not prohibited, but is not tested by Intel...".
As for the feasibility of such a system, it's a separate issue. Given that the difference going either way boils down to $85, let this issue be decided by the original poster.

PS. This post was made from another machine on my home network, based on ABIT BE6 and Intel PIII 850MHz CPU that ordinarily runs 100MHz FSB and the multiplier 8.5. Just for the kicks, I downed the multiplier to 4.5 and ended up with an old 450MHz! Too bad I can't get my hands MP system to try. -;)

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WakeupSpecialist 1Commented:
Hmmm...I have heard both sides of this issue.  Last I heard and I tend to agree with magarity, is that because of voltage issues, Stepping and speed you can not use different CPU's.  And I believe that you can't underclock your cpu either.  But you may be able to try it to see if it works.  I would definitely do what the web site suggests, to check the motherboard manufacturer and see if there are any other issues regarding stepping and CPU Speed etc.

I tend to agree with Magarity as well, however I disagree regarding the underclocking of CPU's. This can be done on some Abit dual-cpu motherboards for example.
Ryan RowleyCommented:
Another problem might be the O/S of choice.
Some O/S's deal better with Dual or more CPU's than others.
Your basic home MS Windows versions might cause some problems.  I have seen MB's with different speed CPU's, but
I have not seen any running with standard MS O/S's.
Someone else might have experience with that. I have heard that standard MS O/S's are picky about such things.
Well that's my 2 cents worth.
OK, there seems to be some confusion over my point about clock multipliers.

BSIM asked if both CPUs could be run AT DIFFERENT SPEEDS.  Not, 'can one CPU or the other be made to match speeds'.  The answer to this original question is a definite 'no'.  BSIM has not written back to ask if it's possible to modify the behaviour of the two chips in possesion, but that seems to be what everyone is answering anyway.  So...

My point is that both need to run at the same speed and that means doing something to either make the 600 faster or the 866 slower.  WHEREBY a Pentium3  866 uses a 133Mhz bus and, WHEREBY a Pentium3 600 uses a 100Mhz bus and, WHEREBY this is a difficult exercise to get them both to run the same speed, THEREFORE it is recommended BSIM simply get another 866 chip for $85.  (Sorry, just read the text of some new law bill in the House right now)  Given the prices of decent dualie motherboards, this is not an outrageous expense to have properly matching CPUs.

Getting the 866 to run slower is probably possible if you are determined to do so and promise not to complain if it turns out to be unstable.  Getting the 600 to run faster won't work at all because of the bus speed increase.  A dualie 866 for $85 is better than a dualie 600 using a crippled 866.

Ryan RowleyCommented:
It is far better to upgrade to the faster CPU's.
I'm with Magarity on that point. Overall performance to
price ratio is a no brainer here.
Sorry, couldn't get on all morning...  Let me jump on the wagon also. I guess I kinda misread the question too... If BSIM really meant running the board with two CPU's, one at 866MHz and the other one at 600 then I totally agree with everyone. This cannot be done. I thought that BSIM simply wanted to get a board, him being a techie, and utilize his two existings chips, that's what I was making a case for! If that's what you, BSIM, really want to do then getting the 866MHz to run at a slower speed is really not a problem. The board will run at 100MHz FBS and with two 600MHz chips. This was my suggestion from the technical angle. However, I agree with magarity on the fact that it may be better spend the extra $$$ and get the second 866MHz chip to match the first one. This extra $$$ also buys you a bit more horsepower, after all, that's what we're all after, otherwise BSIM wouldn't be asking this question to begin with -:).

BSIMAuthor Commented:
hi pple,I want to get CPUs at different speed to run on a mainboard. I know of sun machines allowing 2 different speed, sparc CPUs to run on a mainboard,hence,thougt that maybe Intel machines can do the same.
Ryan RowleyCommented:
Yep Suns and many other Unix world machines will do that.
I believe there are intel boards that can do it, but I don't think that any of the standard versions of the MS O/S's can support that operation. MS uses the CPU's differently than the UNIX world. I don't think any MB designed exclusively for MS O/S's would be able either.
This is an Intel x86 design issue and has nothing to do with any operating system, Unix, Microsoft, or other.  Some specialized x86 systems may have different speeds but those will be more like two systems in one than a standard unified dual CPU system.  Good luck finding such a machine for less than 15,000$US.
BSIM, so for your original question, I think it can't be done. I wish I could add something more helpful Sorry!

Ryan RowleyCommented:
magarity - both are an issue. Intel based MB that would
do it would be much more expensive. However O/S along with
it's drivers are a limiting factor. I have worked with
system exceeding 10 and 12 Cpus. Can't just load any old O/S on them. I think MS's standard O/S's only support 2.
I think their more expensive Server versions support more.

The O/S drives the hardware. O/S includes Bios, drivers and
higher level kernel programs.
"I have worked with system exceeding 10 and 12 Cpus"

That's all very fine but those certainly weren't random speed Pentium 3s scavanged from other PCs.  Other architectures are not being debated here.  Off the shelf dual CPU x86 workstations do NOT mix speeds.

"I think MS's standard O/S's only support 2."

This is a tangent discussion to the question at hand, but I've installed WinNT 4.0 Server out of the box onto a 4 way Pentium Pro machine without modification.  I don't know NT's final limit.  Other MS OSes vary - NT Workstation, 2k Pro, and XP Pro state on the box they are good for 2 way only.  2K Server states on the box it is good to 32, but unfortunately I lack a machine upon which to test this.  A quick check of HP's website shows their 8-way Xeon servers come with 2K Server installed.  Intel's spec calls for 128 CPUs but the most I've ever heard about is a 64 CPU Xeon machine Intel made as a proof-of-concept demonstrator.  It's cost prohibitive to have so many when it's easier to make a Beowulf style cluster of independent machines at those numbers of processors.  x86 is a nasty architecture anyway and you definitely want something else if you need so many processors in a single machine.

All of this is moot because it is not even close to what BSIM is asking.  The answer to this question is: Off the shelf dual CPU x86 workstations do NOT mix speeds.
Ryan RowleyCommented:
All of this is moot because it is not even close to what BSIM is asking.  The answer to this question is:
Off the shelf dual CPU x86 workstations do NOT mix speeds.

Think we are all agreed on this answer for this question.

Just pointing out that the O/S does have a roll and your

This is an Intel x86 design issue and has nothing to do with any operating system, Unix, Microsoft, or other.

Is not true in all circumstances. Don't care how many CPU's
you have, if the O/S does support it, it won't work.

I deal with lots of strange systems and I have written
small special purpose O/S's before to burn onto ROM's.

Software and Hardware must work together.

I have seen a system with different speed x86 cpu's but the
hardware was not designed to run MS windows. The system
had many cpu riser cards in it and they could all be of different speeds. A version of Unix was designed for it.
Ryan RowleyCommented:
I think Magarity gets the point here.
Ryan RowleyCommented:
oops point = points
WakeupSpecialist 1Commented:
Amen!  Now give it to him! :p
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