[TUHS] Old mainframe I/O speed (was: core)

[Arrigo Triulzi]

On 21 Jun 2018, at 16:00, Paul Winalski <paul.winalski at gmail.com> 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”?

I seem to recall there was also some trickery at the CPU level so that you could “field upgrade” between two models by removing it but a) I cannot find the source and b) my Pugh book is far and cannot scan through it.

Arrigo