CPU Power question...

L

L0s7 4 Lyf3

Limp Gawd
Joined
Mar 3, 2004
Messages
454
Yep, you read the title I have a question about powering CPU's...

What reasons did CPU makers have to switch power draw over to the +12V Rail? What advantages does it have over +3.3V or +5V?
 
lots of reasons.

The main one is current - if you have a CPU pulling 100W on a motherboard, the Vcore regulator will pull >20 amps from the 5V rail. This is a lot of current to move around... at 12V, the current required is >8.3A - less than half. >20A requires thick PCB traces, heavy cabling, and so on.

You can more efficiently make a power supply that produces low current at high voltage, than a power supply that produces high current at low voltage. So your computer's PSU runs a bit cooler and draws less power from the wall.

And load regulation became an issue - lots of stuff in your computer (PCI cards, hard drive controllers, USB devices) run on 5 volts, and the 5V rail has to be stable. In your average linux box with a Prescott, your computer's CPU changes its power demand from 10W to 100W hundreds of times a second! and this causes immense current swings on the 5V rail, causing it to "jump around", possibily making your computer unstable. Few things in a computer require that the 12V rail is steady - normally it's just used for electromechanical things (fans, hard drive spindles, etc) which don't care if they're getting 10V or 14V. So moving the CPU regulator there made sense, since it keeps crap off the 5V rail.
 
bump

(was looking for something else when this elegant explaination appeared before my eyes :p )
 
ahem errr...yes however


AMD Power Monitor Version 1.0.1
http://www.amd.com/us-en/Processors/TechnicalResources/0,,30_182_871_9706,00.html
This application is used to monitor the current frequency, voltage, utilization, and power savings of each core of each processor in a system. This application also has a system tray icon that can be used to view and select power schemes on the system. The system tray icon will show the average utilization of every core on the system.
for AMD Athlon 64 Processors

released this month :p

however it only supports XP XP-64 W2K3 and W2K3-64
 
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