Int 15 Fn 88  - System - Get Extended Memory Size (286+)                   [B]

   AH = 88h

Return: CF clear if successful
       AX = number of contiguous KB starting at absolute address 100000h
   CF set on error
       AH = status
       80h invalid command (PC,PCjr)
       86h unsupported function (XT,PS30)

Notes: TSRs which wish to allocate extended memory to themselves often hook
     this call, and return a reduced memory size.  They are then free to
     use the memory between the new and old sizes at will.
   the standard BIOS only returns memory between 1MB and 16MB; use AH=C7h
     for memory beyond 16MB
   not all BIOSes correctly return the carry flag, making this call
     unreliable unless one first checks whether it is supported through
     a mechanism other than calling the function and testing CF

See Also: AH=87h,AH=C7h