[Info-vax] OpenVMS.Org quick pool

[Paul Sture]

On Thu, 23 Aug 2012 16:28:25 -0400, Stephen Hoffman wrote:

> On 2012-08-23 18:05:57 +0000, Johnny Billquist said:
> 
>> No point. You cannot address more than 64K with a PDP-11, so even if
>> you had 1 MB, you could not address it.
> 
> You're referring to the 16-bit addressing design of the PDP-11, most
> likely.
> 
> Later PDP-11 systems support 22-bit memory addressing.
> 
> And shuffling mapping tables also permitted accessing more than 16-bits
> of memory (though not all at once), using windowing.

Our 11/34 running RT-11 had a memory management unit (MMU) which allowed 
RT-11 V3 to reach memory above 64K; we ended up with 192K or slightly 
more in that system.

Since we were using CTS-300 (a Time Shared Dibol monitor which ran 
programs on our behalf) it was transparent to the programmer, though once 
we moved to using MMU, the linker used a base address which resulted in 
over-large executables, and Digital provided a utility called REDUCE 
which trimmed the disk space used back to sensible levels.

This didn't mean that any Dibol program could exceed 32K, just that we 
could run more of them concurrently and hence support more users.

> The same basic window-mapping hackery was performed as far back as Apple
> II systems and very likely before;

This was circa 1978/9.  According to the RT-11 Wiki, use of extended 
memory was available with an MMU as far back as 1975.

https://en.wikipedia.org/wiki/RT-11#Release_history

I note from the release history there that RT-11 v3 dates from Feb-1977. 
This was supposed to support MMU addressing but was sufficiently buggy 
that we had to wait for v3B.  Seeing a menu record appearing in the 
middle of your parts file was a bit of a surprise :-)

-- 
Paul Sture