centos 4 installed on P4 won't boot on P3

[admin at homemachine.net (Tom)]

William A. Mahaffey III wrote:
> Tom wrote:
> 
>> Hi,
>>
>> I installed centos 4 on a P4, configured it (and it booted fine here) 
>> then sent it to the DC to be put in a P3 but it won't boot, displays 
>> GRUB and halts.

>> Any clues? Is there some difference between P3 and P4?
>>
>> thanks
>> tom
> 
> 
> 
> Application code compiled for a P4 (using full P4 optimizations) usually 
> won't run on a P3, I suspect the same for kernels. I betcha you need to 
> do the install again on the P3. I also betcha if you did the P3 1st & 
> then moved that disk to the P4 it would work. Newer CPUs can usually run 
> older code, but not vice-versa. YMMV & all that :-).

it doesn't even get to the grub interface, just the word GRUB on blank 
screen :(