My first CPU, designed and built as a lab project in 1971, used 16-bit
registers and memory words, but the data paths were 1-bit serial. The memory
was implemented with a ~9ms acoustic delay line, in which 8192 recirculating
bits were stored. One of the neat aspects of this design is that one could
continuously view all of memory with a single scope probe! It was unique in
its use of a then-newfangled touchtone keypad for entering hexadecimal
values into registers, replacing the individual toggle switches customarily
used for that purpose. To prove its completion, we programmed it to perform
BCD division; after literally seconds of flashing the lights attached to its
registers, it halted with the correct result ablaze and the TA intoned "it
lives". It was a defining moment...

73,

Dave, AA6YQ


wrote in message ...
"Geoffrey G. Rochat" writes:
....[snip]....
You can do an awful lot on a computer with only 8 instructions that can
directly address a mere 256 12-bit words at a time - if you're willing to
think a little bit. PDP-8s are to computers what regens are to radios:
....[snip]....

You can also do an awful lot on a computer with only 8 instructions that
can directly address only THIRTY-TWO NINE-bit words at a time:

In 1969, while at Fairchild R&D Lab in Palo Alto, CA, I designed and
built a 9-bit PDP-8 imitation (I called it "MINUS", since it was smaller
than a mini-computer; if I had called it "MICRO", I might now be rich!)
with 512 9-bit words of 200 nsec memory. Its instruction format used
a: 3 bit opcode,
1 bit current page/page zero indicator,
1 bit indirect indicator, and a
4 bit address

I also wrote a cross-assembler (in FORTRAN) for it, interfaced it to a
20Kbyte/second magnetic tape and a 3-foot x 5-foot flat bed plotter,
and wrote a program (in MINUSASM) which, in a tight loop, read mag-tape
printed-circuit wirelists produced on an IBM 360/44, buffered them in
the upper half of memory, and then passed them to the plotter to draw
large PC boards. Just before quiting time, we'd load a new mag tape,
and 5-6 hours later another board had been drawn in three colors
(horizontal, vertical, and vias).

Ah, those were the heady days of youth!

--Myron A. Calhoun.
--
Five boxes preserve our freedoms: soap, ballot, witness, jury, and
cartridge
PhD EE (retired). "Barbershop" tenor. CDL(PTX). W0PBV. (785)
539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle,
Pistol)