On Mar 22, 2021, at 19:21, Stan Sieler wrote:
> 
> Re:
> 
>> locate it on the SUBSYS tape, and even though the commands are present
>> (STARTCACHE, STOPCACHE, CACHECONTROL), STARTCACHE results in "disc caching
>> is
>> not enabled on this sytem".
>> 
> 
> FYI, when Classic MPE gets compiled, two of the segments that are generated
> (from two different source files)
> are "CACHESEG" (from source file S5ES002C), and "CACHESEG" (yes, same name;
> from source file S5FS002C).
> The former is the real code for disc caching, the latter is dummy routines
> (so the rest of MPE, which refers
> to disc caching routines in various places) can be linked together.   The
> dummy routines will result
> in messages like "disc caching is not enabled on this system".
> 
> That said, it's probably relatively useless information :)

Based on that, I’m guessing the desired USL from the SUBSYS tape is named something like [log in to unmask], and indeed on the Release 23 SUBSYS tape there is U5EU281A.USL.SYS.

I am thinking DS/3000 and NS/3000 do this sort of thing differently, there’s are some plabels somewhere (system global area?) that are the real guts of CXDSLINE and CXREMOTE, and those command executors test the plabels to see if they can be called and if not they report CIERR 647 (“DS SUBSYSTEM NOT FOUND”, on V/R).  

-Frank McConnell

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