What is the 3.3v wire on S-ATA drives used for?

[MVC]

I was just modding a PSU for a new build and I was out of black 5-circuit plugs so while the dye is drying on a couple white ones I figured I'd ask. The S-ATA drives have the old 4-pin molex plug and the few times I've used it the drive seemed to work OK. Since I'm modifying the wiring anyway I am bringing the 3.3v wire as well (hence the 5-circuit plugs) but I was wondering what the 3.3v is actually used for.

[MadMan007]

I was wondering this recently myself. It doesn't seem to be truly needed since some motherboards provide adapters. Then I looked at the little pictures for installation on a SATA HD and a DVD-RW and they both only show 4 wires, the same 4 that come from a 4 wire molex, going into the SATA power plug. This convinced me not to worry about that 5th wire.

[CougarSE]

Without it Sata Hotswaping does not work.

[JCLW]

For future drives. IIRC when 2.5" drives go mainstream they will use 5V & 3.3V.

Some flash based drives work on 3.3V, as well.

Current 3.5" drives use 12V and 5V.