On Sat, 14 Jul 2018 14:18:24 +0100, Graham. wrote:

====snip====


Makes you wonder why the 3.25 SATA drives still need +12v & +5v

Not 3.25, it's 3.5 (inch). :-)

It doesn't make me wonder why. It's quite obvious if you give it any
thought and remember that the larger internal desktop HDDs all use the
power of a 12v BLDC motor to spin their platters at 5400, 7200, 10200 and
even 15000rpm (though the advent of SSD technology has rendered those
last two speed options obsolete now). The +5v (along with the +12v) are
legacy requirements.

Even though every SATA interfaced SSD drive I've seen have all been 2.5
inch drives and (just like their larger 3.5 inch cousins) are endowed
with the +3.3v option, none to my knowledge actually utilise it as an
alternative to the +5v line. At the very least, all SATA SSDs will run
just fine off the +5v (and ground return) lines alone. There's no need to
provide the +3.3v as anyone who has ever used a 4 pin Molex to SATA power
adapter should be only too aware.

If any of those power rails are eventually to become obsoleted, it's
more likely to be the +5 and +3,3 volt rails, That "Legacy +12v line"
will most likely become the 'defacto' standard for distributing DC power
to everything in PCs and IT kit in general simply because of the ease by
which the actual chip voltages required can be generated by commodity on-
board dc-dc switching regulator chips.

--
Johnny B Good