Robert Redelmeier wrote:
> > The chips between the CPUs and the AGP slot, however, are
> > very hot - what are they? I assume the APIC is a chip -
> > perhaps near here? Would cooling OTHER motherboard chips
> > than the CPUs or the BX greenie help stability?
>
> Those device aren't really chips, they're voltage regulators
> to supply ~2.0V and 1.5V to the CPUs.
Well, according to my definition they're chips alright. How do you
define "chip" so that these are not?
They don't do computations. They don't deal with data flowing through
them at 100MHz speed.
They do have to cope with the CPU moving from 0 to 500 in 10ns.
A halted CPU will draw little current. When it suddenly starts running
again, it will start drawing the normal amount of current. Due to the
enormous speed at which this happens the power supply doesn't notice
this until it's too late (the electrical engineers call this
inductance). That's why we need those capacitors near the CPUs.
> Cooling them isn't as important as chips, but it doesn't hurt.
If they get too hot they burn out. Running a CPU at 1.5 times rated
speed uses up 1.5 times as much current. Running it at 1.1 times the
rated voltage uses up 1.1 times as much current. So all in all, you're
pushing about 1.65 times as much current through the processor. The
heat in the voltage regulator will increase accordingly.
Hot chips are a bit slower, so they may even react slower to the
current surges, requiring larger capacitors near the CPU.
> It appears to me that they're heatsunk into the board via the solder
> tab.
Agreed.
> I believe APIC is built-into the CPUs, or maybe the BX.
I thought that every Pentium Pro and higher had one builtin, but then
there is the IO-APIC, that is on SMP motherboards(*)?
Roger.
(*) and on a few rare non-smp boards.
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