Pwr supply for both Pentium 4 and Core 2 Extreme

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If I have a motherboard that accepts all of the socket 775 processors
(EVGA nForce 680i SLI), I get the impression that one still needs
different power supplies for the different chips. If I get a power
supply that will work with the core 2 quad core (extreme?), will it
also work with say a Pentium 4 chip in other words? I know one meant
for the older chips can't be used for the newer but it seems the
reverse is also true (not backwards compatible as is the motherboard).

I want to use a less expensive chip now then upgrade later if I see the
need and as the prices go down. I'm going to load up on memory and use
the Raptor hard drive so maybe the chip speed won't be as much of an


Re: Pwr supply for both Pentium 4 and Core 2 Extreme

The motherboard's design and electrical requirements determine the PSU
needed, not the CPU.


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Re: Pwr supply for both Pentium 4 and Core 2 Extreme

WannaKatana wrote:
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QX6700 quad core is 130W.

X6800 dual core is 75W.

965 Extreme Edition LGA775 is 130W.

I'd say there is no difference between the old and the new,
in terms of the peak. 130W seems to be the max spec.
130W/12V * (1/0.90) = 12.03 amps of current. A 2x2 ATX12V power
connector, has two yellow 12V wires, each with a capacity of
6 amps. Thus, a 130W processor, uses the full capacity
of a 2x2 connector. That is why some motherboards have
a 2x4 power connector. A 2x4 connector would allow processors
up to 260W to be used, but LGA775 socket also has a say
in the matter, and the socket itself will have a limit
as to how much power can flow through the socket pins.
I have no idea what the engineering limit is for
socket LGA775.

If you were to overclock one of the 130W processors, I'd
be careful to use the 2x4 connector at that point. Similarly,
if you were running a Pentium D 805 at 4GHz, I'd probably
want a 2x4 connector as well. If you are running a 130W processor
at stock speed, a power supply with a 2x2 connector, may do
the job just fine. The power supply itself, will need a
12V2 rating of at least 12 amps, to match the load of a
130W processor. A couple more amps on that rail would not
hurt, if you are going for such a high power processor.

In the equation above, there is an assumption that the
Vcore converter is 90% efficient. I have no figures
to show what the average motherboard is able to
achieve these days. 90% is a pretty optimistic number.
With a lack of good motherboard pictures, I cannot track
down the Vcore regulator chip, pull a datasheet, and read
up on the details. No two motherboards will be exactly the

If it was my motherboard, I wouldn't be too concerned
about using a 2x2 connector in a 2x4 motherboard. If I
was doing some extreme overclocking, that is when I would
put more effort into planning my build. At that point,
a power supply with a 2x4 might make sense. You can
compute expected power drain, via FCV**2. (I.e. Power
increases linearly with frequency, and power increases
as the square of the Vcore increase. Moving Vcore from
1.3V to 1.4V, uses 1.4x1.4/1.3x1.3 or 1.16x as much power.
You multiply the nominal power, by the scaling factor,
as in 130W * 1.16 for that Vcore increase example.
If the core frequency went up by 50%, and Vcore increased
from 1.3V to 1.4V to achieve the overclock, then the
power is 130W * 1.16 * 1.50 = 226W. I'd want a 2x4
power connector for that. And 226W would be 12V @ 20.9A,
which is more than you can get from a typical power
supply 12V2 rating.)

Cooling an overclocked 130W processor is a nightmare.
Same as trying to cool a D 805 at 4GHz. Chances are,
if you have such a rig, you won't enjoy sitting next
to it. If you use water cooling, maybe the noise won't be
too bad, but the room you sit in, is going to get hot.
And we haven't even talked about the video card yet,
like 145W for one of the new Nvidia 8800 series cards.

It is good to plan for the future, but if you buy all
components with future proofing in mind, it can make
for a very expensive computer. Like, if you bought an
1100W ATX power supply, because you thought Nvidia might
have a nice pair of SLI cards two years from now, the
power supply would cost as much as your new processor.

As far as what processors the motherboard supports, you
can check with the motherboard manufacturer's "CPUsupport"
web page, and verify that all the prospective processors
you are interested in, will run in it. This is an
example of such a page. This motherboard appears to
run just about anything that fits in the socket. I
don't see such a page on the EVGA site.


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