>Richard Cini wrote:
Jerome -- good point about the IOPAGE. Maybe I'll get an 8kw and 16kw board -- that gives me 28kw with the included 4kw. I have no specific software so I don't need to tinker with reducing IOPAGE.
Rich
On Feb 9, 2016, at 10:47 PM, Jerome H. Fine <jhfined...@compsys.to> wrote:
Thanks guys. This is really helpful. I was getting confused between the M8044
and M7944 boards. Max memory for the LSI-11 is 32kw, right?
Correct, the maximum memory on a board is 32kw.
For an LSI-11 (aka PDP-11/03) without any MMU hardware,
the actual maximum memory that can be accessed must also allow
for the IOPAGE registers. Usually, the IOPAGE address range
is 4 kw which leaves 28kw for everything else, including RT-11
(assuming that is what you are running). There is one option
available with some hardware to reduce the address range
set aside for the IOPAGE to just 2kw which then leaves
30kw for everything else. Unless you are running a specific
program which requires the extra 2kw, it is probably not
worth the extra effort.
I hope that my version of arithmetic is for 8kw + 16kw = 24kw,
so somewhere I don't understand where the other 4kw comes
from.
Then, since you are missing only 4kw out of the maximum of
28kw (which is the normal maximum), you will not likely have
a problem unless you have really memory rich programs.
RT-11 runs fairly well in just 16kw (or 32 KB), so it should not be a
problem. For my own work in which I need to run MACRO.SAV
as fast as possible, I run the program in 64 KB of extended memory
under a Mapped Monitor - which a PDP-11/03 (or an LSI-11)
can't do since there is no MMU chip.
Of course, my actual CPU is a Pentium III which I use to run Ersatz-11
so that RT-11 is running 15 times as fast as a PDP-11/93. And the
disk I/O is also a bit faster. I can copy a 32 MB RT-11 partition to
a second 32 MB RT-11 partition in under 2 seconds. Even with two
ESDI hard drives on a PDP-11/93, that takes over 4 minutes.
Jerome Fine
