[TUHS] UNIX on S/370

[Ron Natalie]

> I get that PDP-11 and VAX used memory mapped I/O but was that somehow
exposed above the device driver layer?  If so, I missed that, because I had
no conceptual or technical problem with talking to an I/O 

> channel, it was pretty easy.  And I suck at writing drivers.

There's nothing that restricts a device driver to memory mapped I/O.    You
do what ever you have to do to initiate the I/O.   Even the x86's originally
used special instructions to start the I/O (in/out).    The DENELCOR HEP
supercomputer (we did this port around 1983) we had to bounce I/O requests
off a separate I/O processor different from where the kernel was running.
Similar constucts were used on other machines.