Good memory board for Heath H-11?

Jerome H. Fine jhfinedp3k at
Wed Feb 10 14:05:10 CST 2016

 >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. 
>>>On Feb 9, 2016, at 10:47 PM, Jerome H. Fine <jhfinedp3k at> 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

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

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