Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!oakhill!mattp
From: mattp@oakhill.UUCP (Matt Pressly)
Newsgroups: comp.sys.ibm.pc
Subject: System Board RAM above 640K (long)
Message-ID: <1890@oakhill.UUCP>
Date: 7 Mar 89 17:34:12 GMT
Reply-To: mattp@oakhill.UUCP ()
Organization: Motorola Inc. Austin, Tx
Lines: 73

I recently got a CompuAdd 286/20 with 1MB RAM on the system board, and
I am a little confused as to how this memory can be used.  The users'
manual states that memory above 1024K can be used as extended -- I 
assume this refers to the memory you can put in the 4 SIMM slots.  It
also states that the memory between 640K and 1024K (the unusable memory)
is for ROM shadowing and system useage.

[I'm beginning to think there are 3 categories for the memory in excess
of 640K:  extended, expanded, and inaccessible.]

I've got 64K of the 384K used for ROM shadowing, but that leaves 320K which
seems to be inaccessible.  Here are some questions that I have about
that inaccessible memory.  I would greatly appreciate any answers anyone
can provide.

   (1) What does the manual mean by saying this memory is for system 
       use.  It doesn't appear to be used AT ALL.

   (2) Is there any way to use this memory as extended memory?
       The setup program doesn't allow me to do that, but is there
       some other way? What about as expanded?

   (3) Are there any disk caching programs that make use of this 
       memory?   From what I've seen, all of the disk caching
       software uses extended and/or expanded and/or base memory
       only.

   (4) Is there a way I can access this memory from programs that I
       write in Pascal/C/Assembly?  Can I access it in protected mode?
       
   (5) If I can access it, how do I go about that?  Do I need to toggle
       some soft-switch to bank switch it in, since it seems to reside
       in the same address space as Video RAM and BIOS ROM and probably
       IO space?  How are the chip selects generated for those chips?
       Note: some of the address decode logic seems to be configureable
       through software, since a setup program, XSET, allows you to 
       specify what memory you have in the computer, and the computer 
       quits working if you tell XSET something which is not so.

   (6) I called CompuAdd tech-support, and they claimed it can't be
       accessed, and that the hardware designers have gone out of
       their was to make it inaccessible (OS/2 and UNIX can't use it,
       according to the technician).  But he did mention that a software
       package called SOFTBYTES might be able to make it useable by
       fooling the computer into thinking that it's expanded/extended.  
       Does anyone know anything about this package?  Will it work?
       If it works, how did they do it?

   (6.5) The technician said that on the high-end '286s, the memory
       was organized the same was as for the 386s.  If you know how
       the 386 memory is structured, that info would be just about
       as helpful to me.  

   (7) Does anyone have a schematic of the motherboard that they'd
       be willing to loan me :-) ?

If anyone can answer any of these questions or just provide any 
information at all about this system-board memory, it would be 
a really great help, and you will be handsomely rewarded with a
copy of any software I write that will use this memory for 
something useful.  Note:  I've seen other computers which use
this memory as extended rather than inaccessible, so I feel like
there's some hope.  I really find it hard to believe that computer
manufacturers would put in memory that cannot be accessed.

                                              Thanks,

                                              Matthew Pressly

      

-- 
address: mattp@oakhill