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From: Johnny Billquist <b...@softjar.se>
Newsgroups: alt.sys.pdp11
Subject: Re: Virtual memory routines on RSX
Date: Tue, 04 Sep 2012 20:52:05 +0200
Organization: Update Computer Club
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On 2012-09-04 19:14, Rob Brown wrote:
> On 2012-09-04, Lee Gleason <lee.glea...@comcast.net> wrote:
>>    Anyone ever seen these used?
>
> Johnny has used them.
>
>>    Have an opinion on whether they are useful?
>
> Last time I looked at them, I thought that they did not expand the
> address space enough to make them worthwhile.  I thought you could do
> more with the PLAS directives, or even just a virtual array.
>
> My 2 cents.

I wrote a rely to Lee, but I can't see it, so I don't know what happened 
to it.

Anyway, yes, I've used the VM library. It's pretty ok, but it has a 
couple of limitations that I find annoying.
1. You cannot free memory. Only allocate.
2. You cannot allocate more than 512 bytes in one chunk.

The VM library in turn uses the DM library, which is actually a very 
useful and nice library.
PLAS directives are nice, but the problem with them is that all RSX 
systems do not neccesarily have the PLAS directive.
Virtual arrays are pretty much no different than the VM library, but 
more restricted.

With the VM library, you can pretty much have 128K of ram to play with 
(if I remember right, but it might be that it is just 64K).

Some of the more known users of the VM library is MACRO-11 and TKB, 
which uses them for the symbol tables and other information. Neither of 
the restrictions mentioned above is a problem in this case.

IND uses the DM library only.

	Johnny