INT 15 - SYSTEM - GET EXTENDED MEMORY SIZE (286+)
        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
SeeAlso: AH=87h,AH=C7h

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