underclocking?

T

twist

New member
I have the ABIT BX-133 mobo. FSB speeds are adjustable for 100mhz or 133 mhz and beyond. I wanted to upgrade processors to P III 933, but running 133 fsb puts the AGP port at about 89 mhz due to a lack of a 1/2 divider. I understand that this is a function of the BX chipset.

Is it possible to clock my AGP card at 89mhz? What would happen if I left fsb at 100 to satisfy agp requirements, and by so doing, underclocked the 933 processor?

My ram is already pc133.

Thanks,
Twist
 
AGP 1x=33 MHz (100 x 1/3)
AGP 2x=66 Mhz (100 x 2/3)

89 is way too high for the AGP card, the system may not be stable. You'll have to run at 100 FSB. The 100 FSB puts the AGP at 66 MHz, and the PCI bus at 33.

Your proc will run at 701 MHz or so. If you want to set this right, change the Mobo.

Sangram
 
I think I just got lucky, but I have the exact same motherboard running a 1GHz at 133 FSB with a 2x AGP card and have never had a problem with it and a GeForce card. I did have stability issues with a Voodoo 5500 card in this same machine and so I switched to a GeForce2 card and the problems went away. The same Voodoo 5500 is running fine in another computer, so obviously there was something in that combination that didn't get along.

While it's likely to be unstable running at 133, my advice is try it and see, cause you never know. Even when it's not supposed to work, it still might depending on the video card. Run it for a couple days and if there's a problem you're likely to see it rather quickly.
 
thanks guys,

What if the AGP card used was a 4x? Could that run on rhe 89 mhz AGP buss?

thanks again,

Twist
 
it should default to 133 with that proc and that mobo i would think. then it wont be tweaking the pci bus or agp. i.e. i have the abit kt7 and it will go way above 133 but at 133 everything stays at its default pci=33 and i wasnt sure what agp runs at by default
if you underclock you will also underclock the processor your buying as its meant to run on a 133 frontside bus. or maybe im just misunderstanding..
twist said:
I have the ABIT BX-133 mobo. FSB speeds are adjustable for 100mhz or 133 mhz and beyond. I wanted to upgrade processors to P III 933, but running 133 fsb puts the AGP port at about 89 mhz due to a lack of a 1/2 divider. I understand that this is a function of the BX chipset.

Is it possible to clock my AGP card at 89mhz? What would happen if I left fsb at 100 to satisfy agp requirements, and by so doing, underclocked the 933 processor?

My ram is already pc133.

Thanks,
Twist
Click to expand...
 
Thanks for all the replies.

After reading a little in my mobo manual, it seems like I should be able to run 133 fsb to satisfy a P III 933, use a 1/4 divider for the PCI buss, and use a 1/1 for the AGP slot with a 4x AGP card. Or does a 4x AGP card still need a 33 or 66 mhz AGP buss?

Or I could always go pci video card if need be.

Twist
 
Whats the point? I don't think I could focus on making music worrying about these things. lol

Ignorance is bliss!!!!
 
maybe im missing something, but if your board is made to run 133 and your processor needs 133 there shouldnt be an issue i dont think. or is the board default 100 and your pushing it to 133????

twist said:
Thanks for all the replies.

After reading a little in my mobo manual, it seems like I should be able to run 133 fsb to satisfy a P III 933, use a 1/4 divider for the PCI buss, and use a 1/1 for the AGP slot with a 4x AGP card. Or does a 4x AGP card still need a 33 or 66 mhz AGP buss?

Or I could always go pci video card if need be.

Twist
Click to expand...
 
Ham,

Correct. The board is able to do 133 and beyond, but as far as the AGP function, it was intended to run at 100.

I of course, never being satified, was hoping to get a little more out of it than it was intended for.

The most encouraging thing, is the reply from JON X, who has actually succeeded in doing exactly what I was talking about.

I was mistaken about being able to run 4x AGP to solve the problem. Turns out the AGP slot should run at 66 mhz no matter what card you have; the speed is then multiplied on the card itself, either 2x or 4x depending on your card.

There are other alternatives however, I could just use a PCI video card, or replace the mobo (last choice), or install a P III 800 instead of a 933. The 800 runs on 100 mhz, and it's all good, except that I'm bummed because for the same price I could have gotten the 933.

Underclocking the 933 doesn't really make sense though, I just wondered what would happen if you did.



Gargamel,

Point? Only that this is fun to learn about and experiment with don't you think? We have these incredibly powerful tools in our hands, and for me it's kinda nice to know how they work. At least a little bit.

Twist
 
I'm running very similar equipment. Abit BX-133 RAID and a 933 MHz PIII. However, I also running a PCI Video Card, so I haven't come up against the AGP problem.

The latest BIOS for the board allows for an 8.5 multiplier for the processor at a 100 FSB. Assuming you could underclock (I'm far from an expert here), you should be able to clock at 850 MHz with 100 FSB and still set the AGP correctly at 2/3. 933 vs 850 doesn't seem much of a penalty, assuming it can be done.

I guess the issue is can you run a 933-133 Pentium at 850-100 without problems (beside the slightly slower speed)? Not sure also if there is an issue with your 133 memory if you run the FSB at 100.
 
The 133 SDRAM isn't gonna care if the FSB is running at 100Mhz, so that will be fine. The AGP on that BP-6 I thought was only 2x, which I guessed that if you put a 4x card in there it would only run at 2x AGP... or in other words the video card would be limited by the bandwidth of the AGP slot when using the system memory. I could be wrong about how it works, but it's working for me. Still shouldn't be that much a performance hit even if the 4x card is at 2x, especially for recording software purposes. :D

I can't explain the details of the theory about AGP, FSB, and whatever else... but I can tell you from experience that it will work with that mobo and what you are trying to do, cause I've done it twice. You got the right idea about the video card, as that would be the thing to replace. I love that Abit mobo... I have 2 BP-6, a BL-7 Raid and another Abit dual celeron that I can't remember the name for right now, and all of them are great.
 
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