Atari ST diskettes

Paul Koning paulkoning at
Mon Dec 7 15:23:59 CST 2020

> On Dec 7, 2020, at 3:17 PM, Chuck Guzis via cctalk <cctalk at> wrote:
> 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).

I remember him writing (dismissively) about the 1620, don't remember him discussing the 1710.  The 1620's obvious issue, apart from the ones you mentioned, is the blocking I/O.  Can't write a multiprogramming system on such a machine.  Dijkstra worked on the first commercial machine that had interrupts standard (the Electrologica X-1).  So he knew how to use and benefit from interrupts; his Ph.D. thesis is an example.

> The standard disk drive was the 1311.

I remember those.  Ours had two, and a disk O/S that used them.  ("Monitor II"?)  One day the system drive developed a leak, spraying hydraulic oil all over the system pack. IBM repaired the leak, bled the hydraulics, and cleaned the pack and heads (with high purity isopropyl alcohol I scrounged from the chemistry department stock room).  Booted up fine afterwards.  Don't try that with modern disk drives.  :-)

> 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.
> ...
> 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.

Not that I know of.  They did offer paper tape, though that wasn't on ours.


More information about the cctech mailing list