Variable Word length CPU

[William Donzelli]

> They never did make a big dent in the punched card world, did they?

And to add to that, later S/3s could be fitted with 80 column card
devices!

> While the S/3 instruction set bears certain similarities to the S/360, I've
> wondered what IBM's logic was for making it so different from the S/360.  I
> doubt that it was technical--the 360/20 was far more brain-dead than the
> S/3 and customers still used them, in spite of the crippled instruction
> set.

The S/3 line was...special. 

I think the bizzare instruction set of the S/3 stems from the the need for
the machine to deal with characters - RPG and such - almost
exclusively. FORTRAN was offered but it must have really sucked.

There are only 30 or so instructions in the whole set, yet a number of
them are for complex string handling (kind of inpressive for a
non-microcode machine to do string inserts, actually). There are no simple
byte level instructions - everything that goes thru the ALUs are strings,
basically. Everything is a string. Thw world is a string to an S/3.

And yes, the S/3 is a real variable word length machine! Yes, you can add
two 569 byte integers with one instruction!

William Donzelli
aw288 at osfn.org