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Which rail give the CPU the power?

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steimm

Registered
Joined
Mar 8, 2002
Hi there!

I wonder, which rail is giving the CPU power?
I've been getting different information from alot of places, everything from the +3.3V to the +12V. What is true?
Is it depending on the CPU, I mean is it a difference between a PII, PIII, P4, T-bird, Palomino, T-bred etc?

Can someone tell me?

/steimm
 
OP
S

steimm

Registered
Joined
Mar 8, 2002
Thx, so then it is most important to have high Ampere on the 5V-rail if I've been voltmodding the Vcore on my motherboard?

/steimm
 

Gemini1706

Member
Joined
Oct 9, 2002
The CPU uses the 12V rail in the Athlon case. Do not know about the Pentium.

The 12V is regulated down to vcore voltages using a built-in regulator in the mobo. I think the 12V line is used becasue you can get alot of power from the supply with lower current (becasue power=Voltgae*Current, ofcourse somw power is lost as loses and heat).
 

overdoze

Member
Joined
Jan 12, 2001
Location
Texas
DaveSauce said:
oh wow...i just noticed that my p/s can take up to 50 amps to start up....im surprised my house doesnt dim when I start this thing up....

high wattage will dim your light like 800W or above. High amps does not mean it is high wattage. Most typical PS draw somewhere in the 200W range.
 

Sonny

Senior TIFOSI
Joined
Aug 3, 2001
Location
VARIANTE ASCARI
I know it to be the 5V rail but AMD sometimes says its the 12V rail & so does THG(LOL) but when my 'puter goes from idle to load I see my 5V drop a little & my 12V jump a little so I believe it to be 5V plus AMD also said that their 2GHz plus chips will need 45A on the 5V rail for it to even run stable now Abit(don't follow the other brands as much) adds a 12V socket on their newest chipset just like on P4 systems. I still think it's the 5V rail.
 

juliendogg

Member
Joined
Nov 29, 2001
Location
NC, USA
i'm goin with sonny on this one, it's my understanding that the cpu is powered off the 5v rail. hence the massive problems that can come from a low 5v rail. my system reboots instantly if the 5v drops to 4.75. does that on occasion as i'm still using an old 250w psu. at idle it's ok, 4.89. not so bad. put the cpu under 100% load and down it goes. usually stops around 4.79 and stays pretty stable. new psu in route :D