Topic: My CPU is running at half speed. What did I mess up? Can I fix it?

[Kid Carrson]

To the group:

I recently put together a PC from scratch.  I've done a couple (with a little help from a friend who has sadly now moved out of state), but this is the first one that I guess I've botched (because I did it all by myself I guess).  I got a Intel P4 prescott processor that's supposed to be running at 2.4 GHs, but is only running at 1.2 GHs.  The FSB speed is also odd, showing a FSB speed of 400. 

I'm guessing that I made the following mistake:

  the motherboard is limited to a FSB of 533 (it's an Intel D845PESV), but I must have bought a processor with a FSB of 800, and its running at only 400 FSB by default in the Bios settings.  If that's the mistake, can I fix it without replacing the CPU with a new CPU with a lower FSB (533)?  Can I adjust the multiplier in the Bios so that I get the proper processor speed, or should I just suck it up and get a new processor with an FSB suitable for the motherboard?

I'm OK with changing the processor since I figure I'd use the existing processor somewhere else in time.  But I'd rather not change if I don't need to change.

Thanks for any thoughts.

Kid Carrson

[Javora]

Assuming this isn't a heat issue and the processor is powering down to protect itself.  You would be better off buying a new motherboard with a 800 FSB.  You will not be able to get the processing power you need by tweaking the bios settings.  You should be able to find a motherboard for about $100USD or less.  Hope this helps.

[Kid Carrson]

Thanks.  I figured I'd need to change one or the other.  I was just hoping for a third choice.

KC

[Just plain old Punisher]

Sounds like either a heat issue or intentional CPU throttling. Do you have any utilities or programs running that monitor the CPU temp or CPU fan status? They might be malfunctioning and causing the CPU to throttle down.

Make sure your power profile is set to Always on in the power control panel.

[The Bar-Abbas Anomaly]

 

This is definitely caused by the MB not being able to support an 800Mhz FSB...   Your CPUs mulitplier is fixed and cannot be (easily) changed, so your board running at 400Mhz times your CPUs 3x multiplier = 1200Ghz. 

I'd guess that it likes 400 better than 533 as a FSB speed 'cause it's a nice round divisor of the 800Mhz that the chip wants, but it may also be that your memory is not capable of running faster than 400Mhz maybe?  (That would be PC2700, I think....)

[Nemesis]

your memory is not capable of running faster than 400Mhz maybe?  (That would be PC2700, I think....)

DDR 400 is PC3200.  DDR 333 is PC2700.

[Nemesis]

  the motherboard is limited to a FSB of 533 (it's an Intel D845PESV), but I must have bought a processor with a FSB of 800, and its running at only 400 FSB by default in the Bios settings.  If that's the mistake, can I fix it without replacing the CPU with a new CPU with a lower FSB (533)?  Can I adjust the multiplier in the Bios so that I get the proper processor speed, or should I just suck it up and get a new processor with an FSB suitable for the motherboard?

I've never built a Pentium 4 based machine so I am guessing here.   As I understand it Intel counts its FSB at twice the actual FSB because it accesses 2 banks of RAM at the same time.  Do you have 2 (or a multiple of 2) banks of memory or just 1?  It also matters (with the motherboards I have used) which order you fill the memory sockets, have you checked to make sure that you are filling them in the correct sequence and not skipping a socket that must be filled to get the dual channel capability you require?

[Javora]

Kid never stated what type or how much Ram he has in his system.  But in this case the Ram isn't the issue it's the motherboard and buying the right one for his processor is the only thing that is going to solve his problem.  The only thing Kid needs to be aware of is if the Ram he has is right for the new motherboard.  If not then Kid will need some new Ram as well, but most motherboards of that generation supported older 2700 as well as the newer 3200 DDR Ram.  So really it is just a matter of carefully selecting a new motherboard for his system.

The only problem I see is swapping out the motherboard, that is not an easy process as it means rebuilding the machine.  Make sure you have a good work space that doesn't build up static electricity like a solid wood work bench on a wood or cement floor.  Make sure you are grounded when working with parts.  Most importantly take your time and you should have no problem swapping things out.  I've seen people swapping out parts in their bedroom with the system laying on their bed on a carpeted floor.  Rushed around trying to get what ever they wanted to do (even if the system was working fine) in under 5 minutes because they were showing off or what ever.  And they sit and wonder why their system won't boot afterwards.  Taking your time, and planing out what you do saves time and aggravation when every you deal with computers like these.

[Nemesis]

Link to compatible processors for that motherboard

It might be easier to just exchange the CPU.

[Kid Carrson]

Guys.   Thanks for the thoughts on this issue. 

The problem indeed was the FSB limitation of the motherboard versus the CPU FSB setting.  Since the Mobo had a 533 FSB limit, the 800 FSB CPU ran at 400.  I swapped CPU's (put in a 533 FSB CPU) and everything worked great.  I'll use the 800 FSB CPU on a MOBO that can handle it when I assemble another system later this year.

Thanks again guys.

KC 

[Nemesis]

Nice to hear the resolution.  Thanks for letting us know.