XMS35.txt

  XMS v3.5 API
  
  XMS v3.5 has been created to allow accessing extended memory beyond the 4 GB
  barrier. 

  To achieve this, the XMS v3.0 API has been extended:
  
  AH=0C8h: query free super-extended memory. Returns in EAX largest free block
           in kB, in EDX the total amount (in kB) of free super-extended memory.
           AX=0 indicates an error.
  
  AH=0C9h: allocate block of super-extended memory. Expects in EDX the
           requested amount of memory in kB. Returns AX=0 if an error occured,
           else AX is 1 and the handle of the block is in DX.

  AH=0CCh: lock a (super-extended) memory block. Expects handle in DX. Returns
           64-bit physical address of locked block in EDX:EBX. Returns AX=0
           if an error occured.

  XMS function 00 (Get Version) will return ax=0350h, that is version 3.50.

  Since the memory beyond the 4 GB limit must be managed exclusively,
  Int 15h, ax=E820h should be intercepted in a way that all memory blocks with
  addresses >= 100000000h are changed from "available" to "reserved".

  In V86 mode, the XMM's 'move extended memory' function (AH=0Bh) will need the
  help of the Expanded Memory Manager (EMM), since privileged code has to be
  executed. The only EMMs that currently support accessing memory beyond 4 GB 
  are Jemm386/JemmEx v5.80+. Their Int 15h API has been exhanced as well.
  
  Register setup for Int 15h, AH=87h: 
   
  - AH: 87h
  - EAX[bits 16-31]: F00Fh
  - CX: F00Fh
  - ECX[bits 16-31]: size of block in words
  - DS:SI: same as the standard ( pointing to a GDT ), descriptors 2 & 3
           defining address bits 0-31 of source/destination region.
  - DX: address bits 32-47 of the source region.
  - BX: address bits 32-47 of the destination region.

   If the call succeeded, the carry flag is cleared and register AH is 0.
   If an error occured ( for example, CPU doesn't support PSE ), the carry
   flag is set and AH is != 0.

  Japheth