"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)

....[snip]....
The Computer Museum is out in Mountain View, California.

There's another Computer Museum in Bozeman, Montana.
It's not nearly as big, but it contains nice stuff.

--Myron.

--
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)

....[snip]....
The Computer Museum is out in Mountain View, California.

There's another Computer Museum in Bozeman, Montana.
It's not nearly as big, but it contains nice stuff.

--Myron.

--
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)

"Dave, AA6YQ" wrote in message
news:lARab.522300$YN5.348403@sccrnsc01...
No cheating! If you're going to homebrew a PDP-8, you have to build it out
of discrete TTL.

I had my PDP-8S work-alike operational about 30 years ago. I built it from
TTL.

"Dave, AA6YQ" wrote in message
news:lARab.522300$YN5.348403@sccrnsc01...
No cheating! If you're going to homebrew a PDP-8, you have to build it out
of discrete TTL.

I had my PDP-8S work-alike operational about 30 years ago. I built it from
TTL.

"xpyttl" wrote in message
...

Anyway, as we were first looking over the thing, with it's racks of cards
and beautiful, huge electrolytics in the supply, my assistant advisor taps
me on the shoulder and says "come look at this. See that rack of cards
there? I think it's the accumulator."

Sure enough, 18 cards for the accumulator, 18 cards for the program
counter,
18 cards for the M register, one card per bit!

I built my home-brew PDP-8 in a bit-slice way. Each of the main cards had
one bit of the accumulator, memory data register, memory address register
and the "other" register - 12 cards for the main data paths.

As an ancient aside, the "first minicomputer" Whirlwind at MIT was a 16-bit
bit slice machine. There was one whole 6-ft rack for each slice. Thus the
main part of the machine took 16 racks. I never saw the beast, but we (at
USAF Cambridge Research Labs) did do an experiment or two with it driving
our ground to air digital data link. That was in 1953, IIRC. But I was
VERY young back then.....

73 de bob w3otc

"xpyttl" wrote in message
...

Anyway, as we were first looking over the thing, with it's racks of cards
and beautiful, huge electrolytics in the supply, my assistant advisor taps
me on the shoulder and says "come look at this. See that rack of cards
there? I think it's the accumulator."

Sure enough, 18 cards for the accumulator, 18 cards for the program
counter,
18 cards for the M register, one card per bit!

I built my home-brew PDP-8 in a bit-slice way. Each of the main cards had
one bit of the accumulator, memory data register, memory address register
and the "other" register - 12 cards for the main data paths.

As an ancient aside, the "first minicomputer" Whirlwind at MIT was a 16-bit
bit slice machine. There was one whole 6-ft rack for each slice. Thus the
main part of the machine took 16 racks. I never saw the beast, but we (at
USAF Cambridge Research Labs) did do an experiment or two with it driving
our ground to air digital data link. That was in 1953, IIRC. But I was
VERY young back then.....

73 de bob w3otc

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)

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)

Very cool. What did you use for memory?

73,

Dave, AA6YQ

"R J Carpenter" wrote in message
...

"Dave, AA6YQ" wrote in message
news:lARab.522300$YN5.348403@sccrnsc01...
No cheating! If you're going to homebrew a PDP-8, you have to build it
out
of discrete TTL.

I had my PDP-8S work-alike operational about 30 years ago. I built it
from
TTL.