Re: Building computer - power supplies
On 9/27/2013 6:37 PM, Joel Rees wrote:
> On Fri, Sep 27, 2013 at 9:36 PM, Stan Hoeppner <stan@hardwarefreak.com> wrote:
>> A point I forgot to make. This is something everyone should know.
>>
>> Subject: The marketing myth of multiple +12V rails
>> [...]
>
> What I want to know is why Intel CPUs still need the +12V.
They don't now and they never did. The 8088 through 80486 and the first
generation Pentium-60 were 5 volt ICs. The 80486-DX4 and 2nd gen
Pentium were 3.3V. The Pentium MMX through today's CPUs have a dual
voltage plane. The IO section uses 3.3V and the core 1.x-2.x volts
depending on model. The core runs at a lower voltage for higher clock
speed with less current draw and less heat.
As CPUs began requiring more and more juice, specifically the 130W P4
models, it became impractical carry the current across the PCB from the
ATX connector to the CPU socket. A 130W CPU at 3.3V requires 40 amps of
current. Traces in motherboard PCBs are typically made of a gold alloy
deposition. A bare motherboard PCB alone with enough trace metal to
carry 40 amps would need to be on the order of a 12 layer board, and
would simply cost too much due to the additional gold content and
manufacturing complexity.
Installing two voltage regulators next to the CPU socket and using
standard ~22 gauge copper wires from the 12V rail of the PSU solves the
problem cheaply. The 12V rail was chosen because 3.6x less current is
required vs using the 3.3V rail as was used previously, which means much
smaller wires are needed.
If you read about Google's custom servers that power their search
engine, all 6 million of them (exaggeration), they designed their own
motherboard and their own 12V only PSU in conjunction with their
vendors. The PSU supplies 12V to the board through a single connector,
and all conversion is performed on the board.
If you look at any of the big iron from HP, IBM, SUN, SGI, the bulk
power supplies in the chassis supply 48V to each of the many processor
and IO boards, and it's converted down from there at the board level.
This has been the standard for iron for at least 20 years.
> Have you considered copying these kinds of posts to a blog, Stan?
> Might be easier to find them again.
Yes, on occasion. I just never seem to find time/motivation to set it
up and do it...
> (I often do exactly that when I don't want to forget something. Then I
> forget it's in one of my blogs. I mix politics and religion and
> technology and philosophy up too freely in my blogs, even though part
> of the purpose of creating multiple blogs was to separate them by
> purpose.)
If I understand you correctly, in my case blogging it were strictly be
for the benefit of others.
Everything that goes into my posts comes directly from my organic
archive. Sure, I do look some things up on occasion to verify my facts
before posting, or find a link to demonstrate a point, but it's 99% from
memory. I've been gifted with what some folks call a "photographic
memory", though I can assure you that's not a very good description of
how it actually works. Many/most things I can recall instantly. With
others, I know the memory which I'm trying to pull, but finding the
detail within it is akin to being in a boat on a mildly foggy lake, and
I have to paddle around in the fog for a bit before that memory comes
into clear view. I think for most people that fog is simply too thick,
and they don't even try to look through it.
Some people can do this with auditory as well as visual memory. For me
it must go through my visual cortex to have any chance at storage and
retrieval. I know a few women who would say that all men have this ear
to memory problem. ;)
--
Stan
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