Compatibility: EMS 4.0+
Expects: AH    4fH
AL    subfn: 00H=Save some mapping registers
DS:SI=list of registers to query
ES:DI=buffer to receive data
01H=Restore some mapping registers
DS:SI=data obtained via subfn 00H
02H=Query buffer size for subfns 00H and 01H
BX=count of pages to be saved/restored
Returns: AH    EMM status (0=successful)
AL    (subfn 02H) size, in bytes of buffer for data buffers
ES:DI (subfn 00H) buffer contains returned information
Info: This fn is similar to INT 67H 4exxH, in that it saves/restores
the page mapping registers.  This version lets you specify a
subset (e.g., save/restore just one or two pages).

Before using subfn 4f00H, you should use subfn 4f02H to see how
large of a buffer you will need.

DS:SI (subfn 4f00H) is a list that identifies which mapping registers
you wish to save.  The list is formatted as:

Offset Size Contents
+0      2  wPgCnt    number of 16K pages to save
+2      2  wSeg1     segment of first physical pg to save
+4      2  wSeg2     segment of second physical pg to save

ES:SI (subfn 4f00H) is a buffer to receive mapping-register data.  You
should use subfn 4f02H to see how large this should be.

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INT 67H 4fxxH: Get/Set Partial Page Map