9 Dec
2004
9 Dec
'04
11:04 p.m.
On Thu, 9 Dec 2004 21:30:20 -0500, John Allain <allain(a)panix.com> wrote:
Today I started mothballing the VAX 6000 and noticed
that a large part
of its power supply is on 3.3 volts, now common, but probably not in 1988.
Seems like something was invented, probably in chip design that made
3.3 so useful. I wonder what that was, when that landmark was reached.
(For that matter, I don't really know why 5V and
12V were popular, on a "first priinciples" basis.)
Maybe we've lost some of the people on the list who can answer these
questions, but I'm trying anyway.
Well, I think I can answer those two
questions about 5V and 12V,
though I am expecting 40~50 more years to live.
5V is popular because of TTL. TTL is made of bipolar technology on
silicon. Take a look of a simple NAND gate, and tune the voltages of
those transistors for speed, you end up with 5V power supply.
12V is popular because it is a multiple of 2V, which is the voltage of
lead battery. It is also a multiple of 1.5V, which is the voltage of
MnZn battery. Cars used lead bettery, and 12V was chosen (with 6
cells). I think this fact also increased its popularity.
I am pretty sure that the 5V answer is accurate. There might be better
reasons why 12V is popular.
vax, 9000
John A