On Thu, 21 Jun 2018, Arrigo Triulzi wrote:

>> for the microcode to customers.  There were several hacks in there to 
>> slow down the disk I/O so that it didn't outperform the model 30.
>
> Is this the origin of the lore on “the IBM slowdown device”?

If I remember my computer lore correctly, wasn't the difference between 
the Cyber 72 and the 73 just a timing capacitor, if you knew which board?

And I still reckon that the olde 360/20 (I did see the console for one) 
should never have been part of the 360 series;

     * It had a HALT instruction!

     * It had about half the instruction set.

     * Half the number of registers, and width.

     * Floating point?  What's that?

Etc.  A triumph of marketing over engineering...

-- Dave, who did his CompSci thesis on the 360...