Atari ST diskettes

Chuck Guzis cclist at
Mon Dec 7 14:17:15 CST 2020

On 12/7/20 11:50 AM, Van Snyder via cctalk wrote:

> One of my friends changed the tables in a 1620 to do octal arithmetic,
> for telemetry processing.
> Speaking of those tables, do you remember why the 1620 was called
> CADET? Not because it was a "beginner's" or "novice" computer. It was
> an acronym for "Can't Add; Doesn't Even Try."

That was the Model I; the Model II had the math tables hardwired.
Several options were available (and required for some software), such as
indirect addressing and hardware floating point.  A close relative was
the 1710; basically a 1620 with interrupts, real-time clock and various
options for ADC/DAC interfaces for process control.   I believe that
binary arithmetic was also an option, but I'd have to check.

Dijkstra developed a dislike for the thing pretty early on.  One of his
big gripes was that you can't write (to peripherals) everything that you
read.  The other gripe was that there were certain "untouchable"
characters that you could neither test for nor use in arithmetic nor
create, except by reading them (e.g. numeric blank, 8-4 punch).

The standard disk drive was the 1311.

As much as the haters bashed it, it was a pretty reliable workhorse for
the time and a great system for learning fundamentals. (absolutely
uniform instruction layout; no user-addressable registers--all
memory-to-memory), decimal and no fixed word length.

I remember the 1620 SPS coding forms--on one side, cards marked out in
columns for SPS; on the other, the so-called "Absolute Coding System",
which was nothing more than plain machine code.

The 1622 even during its salad days was prone to overheating and
punch-check errors.  One of the hazards running the card-based (no disk)
FORTRAN compiler.

Was there ever a magnetic tape drive for the 1620?  I don't recall ever
hearing about any.  That alone would make it unique among IBM
offerings--card and disk, but no tape.


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