[comp.sys.ibm.pc.misc] hard 80386 questions

grossman@star-trek.bbn.com (Martin Grossman) (03/29/91)

On my 80386 (DX) I have 4 MB ram mem.  I assume its physicaly addressed
startin at 0 (ie 00000000:0000 ).

Theirs also some RAM chips (10 of them) for the cache and shaddow ram.

Their are 2 rom area that nortons SI tells me about in the whole system.
One is on the SVGA board and its address is at C000:0 L 8000 (ie 32K)
The other is on the system board (AMI bios) and is addressed at
F000:0000 L FFFF (ie 64K).


1) Where are those roms within the 80386 address space?  I know it can't
   be within the first 4MB since youd have memory conflicts.

2) When I run the extended CMOS setup and turn off shaddow ram then I can
   tell the system runs slowwer,  BUT after I turn it back on, I go into
   debug and that mem C000:0L8000 and F000:0LFFFF still looks like ROM
   (ie I use the 'e' command to change unused words but the original
   values are still their when I dump it)  (ie It looks like when
   shadow is enabled it copies the rom to fast ram, maps the ram in
   as the rom addresses but disables write accessing...is this right)

3) When I run a TSR that came with the SVGA that copies the VGA ROM
   (I've compared it byte for byte) into low ram (ie within the TSR)
   then video accesses are even faster that using shadow ram.  Why is
   this.  I assumed that shadow ram was some of that (10 chips fast
   ram used also for cache)

4) When cache/shadowram/etc..etc are all turned off SI gives and index
   of 39.9 (this is a 33MHZ system).....when cache.etc.etc are all turned
   on then SI reports 52.3......I don't remember the actual numbers
   but landmarks cpuspeed program show a high improvment BUT only when I
   switch (turbo) to lower 16MHZ setting (cpuspeed bombs out when run
   in high speed mode)


PS does anyone know where I can get ahold of (ANY) source code (assembler)
   of any 80386 BIOS (even one for a different system).  I want to use
   this (in congunction with reading the 80386 hardware manuals) to learn
   all about paging/segments/linear addressing/vitual 8086 mode/protected
   mode etc etc etc


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