Re: Polysemy in programming langs (was: Why does the meaning of words change?)

Ph. D. scripsit:

> Then there was the PDP-8, the first mini-computer IIRC,
> introduced in the 1960s. The only way to store the value
> of the accumulator into memory was via the instruction
> DCA, Deposit and Clear Accumulator. This copied the
> value to memory then set the accumulator to zero.
Yup.  The "accumulator" (AC), for younkers, was the main (and on some
models the only) register, so-called because it was used to
accumulate sums.  The PDP-8's instruction set was small enough
that I still remember all of it:

AND: logically AND a memory location with the AC, leave result in the AC
TAD: add a memory location to the AC, leave the result in the AC
ISZ: increment a memory location; if it becomes zero, skip next instruction
DCA: move AC to a memory location, clear AC
JMS: move the program counter to a memory location, jump to the following
     memory location (the PDP-8's subroutine-calling convention)
JMP: jump to memory location
IOT: I/O instruction: pass one of 8 commands to one of up to 64 devices
     (the meaning of each command was device-dependent)
OPR1: depending on various bits, clear or complement the AC or the "link"
     (condition code), or rotate the AC one or two bits left or right
OPR2: skip next instruction depending on the AC's value, sign, and/or the link

> (The PDP-8 used 4K of 12-bit words.)
Expandable up to 32K.

--
John Cowan  jcowan@reutershealth.com  www.ccil.org/~cowan  www.reutershealth.com
"In the sciences, we are now uniquely privileged to sit side by side
with the giants on whose shoulders we stand."
        --Gerald Holton

Replies