Good memory board for Heath H-11?

Richard Cini rich.cini at
Wed Feb 10 14:24:45 CST 2016

Jerome -- it's "new math" :-)

Seriously though, I guess I could have been a bit clearer in my description, but think I had mentioned somewhere along the way that the unit already had 4kw of memory, so I was trying to get to 28kw to leave IOPAGE open. I also just realized that the boards have a "page 7 disable" which operated like the S100 "phantom" signal which is why a 32kw board would work. Learning lots during this process. Everything I forgot about my 11/34a is starting to come back. 

Sent from my iPhone

> On Feb 10, 2016, at 3:05 PM, Jerome H. Fine <jhfinedp3k at> wrote:
> >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> 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

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