Can a 266 Athlon be run at 200 MHz?

In the higher Athlons, the C in the CPU code -- like AMD Athlon 1400AMS3C -- means 266 Mhz Bus capable.  
Can these CPUs be run at 200 MHz bus?  I have conflicting reports.  50% say they can, 50% say they cannot, they have to be run at 266, they will not work on a motherboard that will only take 200 MHz CPUs.  Anyone with any direct experience running the 266 Athlon on MBs that can only take 200 Mhz?

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dbruntonQuid, Me Anxius Sum?  Illegitimi non carborundum.Commented:
I think I have.  

Had a 1.3 GHz processor with a motherboard that had a jumper switch that changed the FSB of the board from either 100 to 133.  Just looked it up, it was a FIC AM37.  From fogged memory it ran at 100 for most of its life before I realised what was happening.

But your mileage may vary.
In my experience they will.  Multiplier is locked so it will run at about 1100MHz.  Core voltage is the same as other T-bird CPUs and you will not damage the CPU by installing it in a 100 (200) MHz FSB motherboard.

Main concern is whether motherboard will support a CPU with that high a clock multiplier.  Must be a board that can handle an 1100MHz CPU.
scrathcyboyAuthor Commented:
The ABIT board has every setting you can imagine from 88 MHz up to 150 MHz -- but that does NOT mean it works with those CPUs.  I have found it does NOT work with Athlon XP, Athlon 133 or any other CPU other than the ones rated for 100 BUS.  Get this, it will work with an Athlon 1200 at 100 MHz bus, but it will NOT work with a DURON 1200 at 100 MHz bus, this is how quirky these motherboards are !!!
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Is there a BIOS upgrade that provides additional CPU support?
If your motherboard specs say it supports 100MHz FSB it supports 100MHz FSB, I had a problem like this for my computer.

I wanted a Pentium 4 @ 3.4GHz but it was a 533MHz FSB, where my Mobo only supported 400MHz, and if it lowers it to 400MHz it would run @ 2.8GHz, but Im sure they wont work.

If I were you, wait until there is at least 5-10 people saying it will work, then try it.
scrathcyboyAuthor Commented:
Obviously, if a 133 bus CPU is running at 100 instead of 133, it will be = speed/1.33333 = 1200 -> 900, 1400 ->1050.  That is not the point.  The point is, will it actually boot?  I put a DURON 1200 in this MB running at 200 Mhz and it would not boot.  I put an Althon XP in this MB and it would not boot.  I am not going to buy any more CPUs until I know they will boot in this ABIT MB, which only handles 100 bus, even though the CPU jumper switch is set to 133 -- apparently these ABIT BIOS programmers are real losers, 133 doesnt work, even tho the jumper says it does, it doesnt.
dbruntonQuid, Me Anxius Sum?  Illegitimi non carborundum.Commented:
I think its your motherboard that's the problem.  

I had the FIC working, it only had two jumpers not a BIOS selectable settings like you have.  Oh yeah, throw SOYO into that mix as well, I have a number of motherboards from them that say they will support 200 MHz CPUs and I can't get them past 166.
Set the FSB to 100MHz and see what happens.  At 133MHz, you may be grissly overclocking memory and PCI bus.

As stated earlier, BIOS CPU support is also a large factor.  It may not accept a 1200MHz Duron due to BIOS.  Remember, it will ID the CPU type.  Definitely will not support an Athlon XP.  Should support any Athlon T-Bird that meets multipliers in BIOS with FSB set at 100MHz.

I've inadvertently forgotten to change FSB from 100 (200) to 133 (266) MHz several times when installing Athlon Thurderbird CPUs.  They all booted, just at lower speed.

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Errata: grissly = grossly
scrathcyboyAuthor Commented:
"It may not accept a 1200MHz Duron due to BIOS.  Remember, it will ID the CPU type.  Definitely will not support an Athlon XP.  Should support any Athlon T-Bird that meets multipliers in BIOS with FSB set at 100MHz."

Yes, that is the conclusion I came to.  I tried 200/266 jumper, made no difference.  And the ABIT people state any athlon up to 1200, which is what they tested, and any duron up to 850, which is the limit they are testing at the time of FINAL bios update.

Hence these ABIT programmers evidently are ID-ing the CPU.  If it isnt on their list, the board fails to boot.  That I like a car refusing to start if it does not recognize the driver -- guaranteed failure thinking.  An intelligent programmer would check the bus speed, the CPU speed the core voltage and other params and then set that regardless of whether the CPU id was in their table or not.

I am upping points so I can assign a reasonable amount to everyone who contributed.  Thanks.
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