INT 15 - SYSTEM - ENABLE/DISABLE PROCESSOR FUNCTIONS
        AH = C8h
        AL = function
            00h disable cache or (90 and 95) disable cache L1
            01h enable cache or (90 and 95) enable cache L1
            ---models 90 and 95 only---
            02h disable cache L2
            03h enable cache L2
            04h disable both caches
            05h enable both caches
            06h return status of both caches
            07h-FFh Reserved
Return: CF set on error
        CF clear if successful
            AH = status (see below)
        For subfunction 06h only:
            BH = status of cache L2
                00h enabled
                01h disabled or not installed
            BL = status of cache L1 (same codes as BH)
Notes:   supported by at least PS/2 70, 70/486, 80-A21, 90, 95
        call AH=C0h and examine bit 3 of feature byte 2 to check if this
          function is supported.
        on a 486 system, any external caches must be disabled when the
          on-chip cache (L1) is disabled.
SeeAlso: AH=C0h

Values for status:
 00h    operation successful
 01h    function choice (in AL) is invalid
 02h    NVRAM data is invalid
 03h    cache test error
 04h    (90 and 95 only) cannot perform operation requested due to state of
          other cache (see note above)
 05h    no L2 cache is present

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