here is a mid-1960s
Digital Equipment Corporation pdp-8 s
mini-computer they got from David Larsen
of the bug book computer museum in Floyd
Virginia it spent the last week or so
restoring it and getting it running it's
built out of the deck flip chips that
are completely transistorized there are
no integrated circuits there's a four
killer word 12 bit word core memory
module back there and this one has an
external power supply that was in the
base of a straight eight used for some
analog interfaces that I converted to
use with this computer so it's Perry
correct but not the original power
supply here is a typical flip chip
module this one happens to be a NAND
gate and it has transistors and diodes
and resistors and it's very simple
single sided circuit board there's a few
hundred of them in the computer now
we're going to load a small program that
increments the accumulator has a small
delay loop and jumps back so we can see
the accumulator incrementing instead of
having to go by to quickly load address
zero deposit the increment accumulator
instruction this one will be a memory
location of 34 that we will increment
and skip yep zero will jump back to that
instruction
and then we'll jump back to the very
beginning now we'll check it
there's the increment accumulator
there's the increment location memory
location skip next to instruction of
zero jump back to that instruction so
we'll loop until the register zero
memory location to zero and then jump to
the beginning so load address and run
and didn't work because I'm in single
step mode stop turn off two single steps
below the address and start it and there
we go pbps
incrementing its accumulator which is
about all I can do since there are no
peripherals on this machine the memory
location is incrementing that goes
through 4096 steps so there's a 4096
instruction cycle delay and then the
accumulator is incrementing you kind of
slow it shows you how slow the machine
really is it's no speed demon the S is a
serial arithmetic machine all the
registers are transferred in serial
format that's got a serial single bit
adder so it is quite slow compared to
even a straight eight which has all
parallel registers and this much faster
stop and that's it
working PD pas
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