5v rail

[mike_6289]

I know it might sound like a stupid question, but what do modern computers (say SB) use the 5V rail for?

 

[Machupo]

hard drives?

 

[kwiksilver]

usb is 5v

 

[Tsumi]

Hard drives, SSDs, USB, and other components on the motherboard all use the 5v rail. Some people also use the 5v rail to undervolt and slow down any fans they have.

 

[mike_6289]

So in a standard computer eg.

Motherboard
3x HD
2x PCI
1x Vid
2x Optical
4x External USB devices

how many amps would be drawn from the 5v rail?

 

[Tsumi]

Why do you care? It doesn't matter in typical setups. Most important is the amount of power on the 12v rail.

 

[mike_6289]

Why do you care? It doesn't matter in typical setups. Most important is the amount of power on the 12v rail.

It's a curiosity. Does that make my question less valid?

 

[Profumo]

So in a standard computer eg.

Motherboard
3x HD
2x PCI
1x Vid
2x Optical
4x External USB devices

how many amps would be drawn from the 5v rail?

HDD & ODD -> 1A each(the motors in both use 12v)
PCI -> depends on the card in question
USB -> standard USB ports are rated for 500mA
Vid -> what?

 

[Tsumi]

It's a curiosity. Does that make my question less valid?

It will be much less than what the 5v rail on modern power supplies are capable of putting out.

It's hard to measure motherboard power draw, since all the USB pulls from the motherboard. While most USB ports are rated for 500 mA, some are rated for up to 1.5 A, and USB 3.0 can be rated up to 4.5 A. Of course, actual draw highly depends on the device attached to it.

Additionally, different chipsets consume different amounts of power. x58 pulls up to 40 watts or so (don't know which rails), while 1155/1156 probably pull about 10-20.

Modern video cards pull exclusively from 12v.

Hard drives will pull what they're rated for on the label, or less.

PCI cards can pull either from 5v or 3.3v, depending on what they're designed for.