XMS 04H: Global Disable A20
Compatibility: XMS 2.0+
Expects: AH 04H
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Returns: AX status: 0000H = successful
0001H = error and BL=XMS error code
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Info: This disables the A20 line, making the HMA▲ inaccessible
(FFFF:0000 will point to someplace in low memory).
Only the owner of the HMA should mess with this; see XMS 01H
(request HMA).
Notes: ■ Toggling A20 is relatively slow on some machines.
■ TSR owners of the HMA who toggle A20 on popup, should first get
the current state via XMS 07H, and restore that setting before
popping down.
See Also: XMS Functions
Extended Memory Specification (XMS)
DOS Functions
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