10 Feb
2016
10 Feb
'16
12:05 p.m.
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 <jhfinedp3k at 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