Underclocking?

It seems that, at least in some markets, 800 MZh P-3 CPU's are cheaper and
more readily available than 700 MHz ones. Although everything I know about
physics and electronics says that there's probably no real danger in
underclocking an 800 to 700, I thought I'd ask. Is it okay?

TIA
Norm

Are you aware that PIIIs have locked multipliers?

There were two types of PIII 800 CPUs that I know of: 100 MHz FSB (front
side bus) with an 8X multiplier, and 133 MHz FSB (6X). The latter were
usually listed with a "B" suffix.

I'd expect a mainboard designed for a 700 also to be able to use an 800 -
they're both "Coppermine" CPUs. It might not be capable of the 133 MHz FSB,
though, so you might want the correct (non-B) 800.

Good luck.

Bob Knowlden

Address may be altered to avoid spam. Replace nkbob with bobkn.

"Norm Dresner" <ndrez@att.net> wrote in message
news:_xS%b.51103$aH3.1563312@bgtnsc04-news.ops.worldnet.att.net...
> It seems that, at least in some markets, 800 MZh P-3 CPU's are cheaper and
> more readily available than 700 MHz ones. Although everything I know
about
> physics and electronics says that there's probably no real danger in
> underclocking an 800 to 700, I thought I'd ask. Is it okay?
>
> TIA
> Norm
>

Alas, it's not a motherboard but a Single Board Computer (ISA bus). And it
says 700 MHz which, I assume, means that the chip-set isn't qualified for
800 MHz.

Does the "Locked Multiplier" mean that it's the FSB that drives the CPU
frequency or that the CPU frequency is used to derive the FSB?

Thanks
Norm

"Bob Knowlden" <nkbob@comcast.net> wrote in message
news:c1p24o$1lddte$1@ID-135009.news.uni-berlin.de...
> Are you aware that PIIIs have locked multipliers?
>
> There were two types of PIII 800 CPUs that I know of: 100 MHz FSB (front
> side bus) with an 8X multiplier, and 133 MHz FSB (6X). The latter were
> usually listed with a "B" suffix.
>
> I'd expect a mainboard designed for a 700 also to be able to use an 800 -
> they're both "Coppermine" CPUs. It might not be capable of the 133 MHz
FSB,
> though, so you might want the correct (non-B) 800.
>
> Good luck.
>
> Bob Knowlden
>
> Address may be altered to avoid spam. Replace nkbob with bobkn.
>
> "Norm Dresner" <ndrez@att.net> wrote in message
> news:_xS%b.51103$aH3.1563312@bgtnsc04-news.ops.worldnet.att.net...
> > It seems that, at least in some markets, 800 MZh P-3 CPU's are cheaper
and
> > more readily available than 700 MHz ones. Although everything I know
> about
> > physics and electronics says that there's probably no real danger in
> > underclocking an 800 to 700, I thought I'd ask. Is it okay?
> >
> > TIA
> > Norm
> >
>
>

On Sat, 28 Feb 2004 11:03:24 GMT, "Norm Dresner" <ndrez@att.net>
wrote:
>Alas, it's not a motherboard but a Single Board Computer (ISA bus). And it
>says 700 MHz which, I assume, means that the chip-set isn't qualified for
>800 MHz.
>
> Does the "Locked Multiplier" mean that it's the FSB that drives the CPU
>frequency or that the CPU frequency is used to derive the FSB?

Bus speed is used to drive the CPU frequency. Inside the CPU there is
a clock multiplier that clocks the internals of the chip at some
multiple of the bus speed. In almost all modern processors that
multiplier is locked at the factory with no possible way of unlocking
it (this is mainly done to prevent remarking, ie someone taking a
700MHz processor and rebadging it as an 800MHz processor).

-------------
Tony Hill
hilla <underscore> 20 <at> yahoo <dot> ca

"Norm Dresner" <ndrez@att.net> wrote :

> Alas, it's not a motherboard but a Single Board Computer (ISA
> bus). And it says 700 MHz which, I assume, means that the
> chip-set isn't qualified for 800 MHz.

Chipset by itselfe has nothing to do with processor frequency. All it
cares about is I/O and FSB.

Pozdrawiam.
--
RusH //
http://pulse.pdi.net/~rush/qv30/
Like ninjas, true hackers are shrouded in secrecy and mystery.
You may never know -- UNTIL IT'S TOO LATE.

"Tony Hill" <hilla_nospam_20@yahoo.ca> wrote in message
news:941256b1096ccccb90f959c6b8d53de1@news.1usenet.com...
> On Sat, 28 Feb 2004 11:03:24 GMT, "Norm Dresner" <ndrez@att.net>
> wrote:
> >Alas, it's not a motherboard but a Single Board Computer (ISA bus). And
it
> >says 700 MHz which, I assume, means that the chip-set isn't qualified for
> >800 MHz.
> >
> > Does the "Locked Multiplier" mean that it's the FSB that drives the
CPU
> >frequency or that the CPU frequency is used to derive the FSB?
>
> Bus speed is used to drive the CPU frequency. Inside the CPU there is
> a clock multiplier that clocks the internals of the chip at some
> multiple of the bus speed. In almost all modern processors that
> multiplier is locked at the factory with no possible way of unlocking
> it (this is mainly done to prevent remarking, ie someone taking a
> 700MHz processor and rebadging it as an 800MHz processor).
>

AHA! So if I set the board for 100 MHz FSB and put an 800 MHz CPU on
it it would run at 800 MHz. The lower FSB is 66 MHz which would get me a
tad over 500 MHz for the processor. Not what I'd ideally want, but it sure
beats the Socket 7 board with the 233 Mhz MMX I have running in the box now.
It would seem then that the proper course of action is pay the extra
money to get a real 700 MHz CPU which I can run with a 100 MHz FSB.

Thanks for the education.

Norm

"RusH" <rush@pulse.pdi.net> wrote in message
news:Xns949DA41613D73RusHcomputersystems@193.110.122.80...
> "Norm Dresner" <ndrez@att.net> wrote :
>
> > Alas, it's not a motherboard but a Single Board Computer (ISA
> > bus). And it says 700 MHz which, I assume, means that the
> > chip-set isn't qualified for 800 MHz.
>
> Chipset by itselfe has nothing to do with processor frequency. All it
> cares about is I/O and FSB.

Okay. That was a brain cramp.

It's been pointed out to me in a private e-mail that an 800 MHz CPU
would draw more current than a 700 MHz and perhaps overload on-board voltage
regulators.

Thanks for the correction.

Norm

"Norm Dresner" <ndrez@att.net> wrote in message
news:JCc0c.114917$hR.2222628@bgtnsc05-news.ops.worldnet.att.net...
> "Tony Hill" <hilla_nospam_20@yahoo.ca> wrote in message
> news:941256b1096ccccb90f959c6b8d53de1@news.1usenet.com...
> > On Sat, 28 Feb 2004 11:03:24 GMT, "Norm Dresner" <ndrez@att.net>
> > wrote:
> > >Alas, it's not a motherboard but a Single Board Computer (ISA bus).
And
> it
> > >says 700 MHz which, I assume, means that the chip-set isn't qualified
for
> > >800 MHz.
> > >
> > > Does the "Locked Multiplier" mean that it's the FSB that drives the
> CPU
> > >frequency or that the CPU frequency is used to derive the FSB?
> >
> > Bus speed is used to drive the CPU frequency. Inside the CPU there is
> > a clock multiplier that clocks the internals of the chip at some
> > multiple of the bus speed. In almost all modern processors that
> > multiplier is locked at the factory with no possible way of unlocking
> > it (this is mainly done to prevent remarking, ie someone taking a
> > 700MHz processor and rebadging it as an 800MHz processor).
> >
>
> AHA! So if I set the board for 100 MHz FSB and put an 800 MHz CPU on
> it it would run at 800 MHz. The lower FSB is 66 MHz which would get me a
> tad over 500 MHz for the processor. Not what I'd ideally want, but it
sure
> beats the Socket 7 board with the 233 Mhz MMX I have running in the box
now.
> It would seem then that the proper course of action is pay the extra
> money to get a real 700 MHz CPU which I can run with a 100 MHz FSB.
>
> Thanks for the education.
>
> Norm

The thing you have to be careful about is not just 1 thing, there are many
things involved in upgrading to a P3.

First, yes, the multipliers are locked, so it doesn't matter what the manual
says it supports, as long as it supports the proper bus speed.

Secondly, the board must be able to run a Coppermine CPU. You won't get a
board to run a Tualatin unless it was specifically made to do so, or unless
you are using a Poweleap adapter (which has its own set of power regulators,
AFAIK).

Third, the power draw must be able to be withstood by the board. If an 800
takes 70W, and your board can only do 65W, you're out of luck. (These
numbers are completly ficticious, BTW).

So, really, as long as your BIOS supports Coppermine, has the 100MHz bus,
can do the voltage of the CPU, and can give it enough current to support it,
then you shouldn't have any problems with an 800MHz.

Underclocking would be strange to do on an Intel, as you'd end up running an
87.5MHz bus, which is likely to throw off your AGP, and PCI speeds, thereby
making it even more risky.

At the very least, it's a good thing you did ask and not go it alone.

"Norm Dresner" <ndrez@att.net> wrote :

> It's been pointed out to me in a private e-mail that an 800
> MHz CPU
> would draw more current than a 700 MHz and perhaps overload
> on-board voltage regulators.

1-3(hmm maybe 5) Wats more wont do you any harm


Pozdrawiam.
--
RusH //
http://pulse.pdi.net/~rush/qv30/
Like ninjas, true hackers are shrouded in secrecy and mystery.
You may never know -- UNTIL IT'S TOO LATE.

Anonymous Joe <no@spam.plz> wrote:
> So, really, as long as your BIOS supports Coppermine, has the 100MHz bus,
> can do the voltage of the CPU, and can give it enough current to support it,
> then you shouldn't have any problems with an 800MHz.

It might very well work even without explicit BIOS support for Coppermine;
I've done that (P3/800-100fsb, very early revision ABIT BH6), and although
the BIOS-reported speed was wrong, it otherwise worked wonderfully, and the
processor ran at the right speed.

--
Nate Edel http://www.nkedel.com/

"I do have a cause though. It is obscenity. I'm for it." - Tom Lehrer