3 Apr
2008
3 Apr
'08
11:15 a.m.
"Tim Shoppa" <tshoppa at wmata.com> skrev:
Johnny writes:
Guilty as charged on the 11M+ part. :-)
However, I think I covered machines without MMUs as well, I just didn't spell it
out.
Without MMUs are the same as machines with the MMU disabled.
The one thing that differs is who puts out the extra bits on the address bus if
there are more than 16 address bits, when you don't have an MMU.
The CPU do, in those machines.
Oh well. And I thought I'd done a real proper job. :-)
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
The PDP-11 CPU is a 16-bit machine, so all code
will always just deal
with 16-bit values.
The PDP-11 can have different buses, with different behaviours, but
basically we can divide them into three groups.
16-bit bus
18-bit bus
22-bit bus
Machines with a simple 16-bit bus is almost nonexistant, but there was
some early Q-bus CPUs with a pure 16-bit address range, I seem to remember.
18-bit means all Unibus machines, as well as some Q-bus machines.
22-bit means most Q-bus machines.
Obviously written from a 11M+ user's perspective. Ignore all those puny Unibus and
Q-bus machines without MMU, will you? But they still run RT-11 just fine!