On Sat, 2 May 2020 at 20:25:42, Paul wrote:
[]
I've never had an AT era machine here. Completely missed it.

Oh, the original AT - and XT - machines were very satisfying: big cast
(or possibly machined, I'm not sure) cases!

I think the AT missed out on Soft Power. They didn't have
the button on the front. Just a button on the back. When you
saw "It's safe to turn off your PC" on the VGA screen,
you reached for the switch on the back to pack it up for the night.

The really early machines, definitely: big red lever switch on the side.
You definitely knew that was a power switch! However, some towers were
AT era and had the power switch on the front; you could tell as it was a
two-position switch, in for on.

having just looked at an old tower, I've remembered another reason some
cases had two buttons on the front: some had a reset button. I always
felt nervous about that: too easy to hit by mistake! IMO if you're going
to have a reset button, it should always be two in series.

You can see the AT power cable pair, with the pins that go 1-6, 1-6
for a total of 12 pins, there is no PS_ON# like on ATX.
There's no 3.3V either (likely some 5V chips back in the day).

http://www.playtool.com/pages/psucon...onnectors.html

1 orange power good
2 red +5 volts or connector key
3 yellow +12 volts
4 blue -12 volts
5 black ground
6 black ground
1 black ground
2 black ground
3 white -5 volts
4 red +5 volts
5 red +5 volts
6 red +5 volts

And my first PC had "one-phase power" on the motherboard,
the CPU was that weak and unassuming. It ran 300MHz,
until you changed the setup and then it ran 450Mhz,
and you'd go "so what?" :-) That's because RAM was
so bad back then, it ran 300MB/sec, or a bit slower
than your SSD today. And the hard drive did 10MB/sec
(as fast as a cheap SD card today).

Paul

My first PC (after defecting from a different family of processors) was
a 386SX; 25 or 40 or something like that MHz.
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

We no longer make things, but sell each other consultancy on how to run
consulatancies better. (Michael Cross, Computing 1999-3-4 [p. 28].)