Interested in UNIVAC 9000 Series (and IBM 360)

Jon Elson elson at
Fri Nov 18 17:15:54 CST 2016

On 11/18/2016 02:04 PM, Chuck Guzis wrote:
> Models? Wasn't the 9300 basically an 
> instruction-compatible model of the S/360 Model 20? I 
> think the 9400 was the bottom end 360/30 model compatible. 
> Calling the Model 20 a "member of the System 360 line" has 
> always been a bit of a stretch in my book.
OH, yeah!  Besides the limited instruction set, short 
registers only half populated, etc., did you know that the 
360/20 did not have an adder?  It could only 
increment/decrement.  The data paths were only 4 bits wide, 
so to add a 3 in register A to a 5 in register B, it 
decremented A and incremented B until A went negative.  It 
did this for each nibble.  I'm guessing a 16-bit add took 
over 100 us.  I'd ALMOST reject calling this a COMPUTER!


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