INT 15 - SYSTEM - COPY EXTENDED MEMORY
        AH = 87h
        CX = number of words to copy (max 8000h)
        ES:SI -> global descriptor table
Return: CF set on error
        CF clear if successful
        AH = status
            00h source copied into destination
            01h parity error
            02h interrupt error
            03h address line 20 gating failed
            80h invalid command (PC,PCjr)
            86h unsupported function (XT,PS30)
Notes:  copy is done in protected mode with interrupts disabled by the default
          BIOS handler; many 386 memory managers perform the copy with
          interrupts enabled
        this function is incompatible with the OS/2 compatibility box
SeeAlso: AH=88h,AH=89h

Format of global descriptor table:
Offset  Size    Description
 00h 16 BYTEs   zeros
 10h    WORD    source segment length in bytes (2*CX-1 or greater)
 12h  3 BYTEs   24-bit linear source address, low byte first
 15h    BYTE    source segment access rights (93h)
 16h    WORD    zero
 18h    WORD    destination segment length in bytes (2*CX-1 or greater)
 1Ah  3 BYTEs   24-bit linear destination address, low byte first
 1Dh    BYTE    destination segment access rights (93h)
 1Eh 18 BYTEs   zeros

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