--------m-2F4300-----------------------------
INT 2F - EXTENDED MEMORY SPECIFICATION (XMS) v2+ - INSTALLATION CHECK
	AX = 4300h
Return: AL = 80h XMS driver installed
	AL <> 80h no driver
Notes:	XMS gives access to extended memory and noncontiguous/nonEMS memory
	  above 640K
	this installation check DOES NOT follow the format used by other
	  software
SeeAlso: AX=4310h
Index:	installation check;XMS version 2+
--------m-2F4308-----------------------------
INT 2F U - HIMEM.SYS v2.77+ - GET A20 HANDLER NUMBER
	AX = 4308h
Return: AL = 43h if supported
	    BL = A20 handler number (value of /MACHINE:nn switch)
	    BH = AT A20 switch time (00h medium, 01h fast, 02h slow)
Note:	if the A20 handler number returned in BL is 00h, an external handler
	  is being used (see AX=4330h)
SeeAlso: AX=4309h,AX=4330h
--------m-2F4309-----------------------------
INT 2F U - HIMEM.SYS v3.09+ - GET XMS HANDLE TABLE
	AX = 4309h
Return: AL = 43h if function supported
	    ES:BX -> XMS handle table (see #1301)
Note:	HIMEM.SYS v3.09 is part of MS-DOS 6.0.
SeeAlso: AX=4308h

Format of XMS handle table:
Offset	Size	Description	(Table 1301)
 00h	BYTE	??? (01h in HIMEM.SYS v3.09)
 01h	BYTE	size of one handle descriptor
 02h	WORD	number of handles (default = 20h)
 04h	DWORD	pointer to XMS handle array (see #1302)
SeeAlso: #1336

Format of XMS handle descriptor [array]:
Offset	Size	Description	(Table 1302)
 00h	BYTE	flag
		01h=free, 02h=used, 04h=in pool but not associated with any EMB
 01h	BYTE	lock count (00h=unlocked)
 02h	DWORD	address of XMS block in KB (shift left by 10 for abs. address)
 06h	DWORD	size of XMS block in KB
--------m-2F4310-----------------------------
INT 2F - EXTENDED MEMORY SPECIFICATION (XMS) v2+ - GET DRIVER ADDRESS
	AX = 4310h
Return: ES:BX -> driver entry point (see #1303,#1304,#1314,#1333)
Notes:	HIMEM.SYS v2.77 chains to previous handler if AH is not 00h or 10h
	HIMEM.SYS requires at least 256 bytes free stack space when calling
	  the driver entry point
SeeAlso: AX=4300h

Format of XMS driver entry point:
Offset	Size	Description	(Table 1303)
 00h  5 BYTEs	jump to actual handler
		either short jump (EBh XXh) followed by three NOPs or
		  far jump (EAh XXXX:XXXX) to a program which has hooked itself
		  into the XMS driver chain
Note:	to hook into the XMS driver chain, a program should follow the chain of
	  far jumps until it reaches the short jump of the driver at the end
	  of the chain; this short jump is to be replaced with a far jump to
	  the new handler's entry point, which should contain a short jump
	  followed by three NOPs.  The new handler must return to the address
	  pointed at by the short jump which was overwritten.  Using this
	  method, the new handler becomes the first to see every XMS request.

(Table 1304)
Call the XMS driver "Get XMS version number" function with:
	AH = 00h
Return: AX = XMS version (in BCD, AH=major, AL=minor)
	BX = internal revision number (in BCD for HIMEM.SYS)
	DX = High Memory Area (HMA) state
	    0001h HMA (1M to 1M + 64K) exists
	    0000h HMA does not exist

(Table 1305)
Call the XMS driver "Request High Memory Area" function with:
	AH = 01h
	DX = memory in bytes (for TSR or device drivers)
	    FFFFh if application program
Return: AX = status
	    0001h success
	    0000h failure
		BL = error code (80h,81h,90h,91h,92h) (see #1334)
Note:	HIMEM.SYS will fail function 01h with error code 91h if AL=40h and
	  DX=KB free extended memory returned by last call of function 08h

(Table 1306)
Call the XMS driver "Release High Memory Area" function with:
	AH = 02h
Return: AX = status
	    0001h success
	    0000h failure
		BL = error code (80h,81h,90h,93h) (see #1334)

(Table 1307)
Call the XMS driver "Global enable A20, for using the HMA" function with:
	AH = 03h
Return: AX = status
	    0001h success
	    0000h failure
		BL = error code (80h,81h,82h) (see #1334)

(Table 1308)
Call the XMS driver "Global disable A20" function with:
	AH = 04h
Return: AX = status
	    0001h success
	    0000h failure
		BL = error code (80h,81h,82h,94h) (see #1334)

(Table 1309)
Call the XMS driver "Local enable A20" function with:
	AH = 05h
Return: AX = status
	    0001h success
	    0000h failure
		BL = error code (80h,81h,82h) (see #1334)
Note:	this function is used for direct access to extended memory

(Table 1310)
Call the XMS driver "Local disable A20" function with:
	AH = 06h
Return: AX = status
	    0001h success
	    0000h failure
		BL = error code (80h,81h,82h,94h) (see #1334)

(Table 1311)
Call the XMS driver "Query A20 state" function with:
	AH = 07h
Return: AX = status
	    0001h enabled
	    0000h disabled
		BL = error code (00h,80h,81h) (see #1334)

(Table 1312)
Call the XMS driver "Query free extended memory" function with:
	AH = 08h
	BL = 00h (some implementations leave BL unchanged on success)
Return: AX = size of largest extended memory block in KB
	DX = total extended memory in KB
	BL = error code (00h,80h,81h,A0h) (see #1334)
Note:	this function does not include the HMA in the returned memory sizes

(Table 1313)
Call the XMS driver "Allocate extended memory block" function with:
	AH = 09h
	DX = Kbytes needed
Return: AX = status
	    0001h success
		DX = handle for memory block
	    0000h failure
		BL = error code (80h,81h,A0h) (see #1334)
SeeAlso: #1331

(Table 1314)
Call the XMS driver "Free extended memory block" function with:
	AH = 0Ah
	DX = handle of block to free
Return: AX = status
	    0001h success
	    0000h failure
		BL = error code (80h,81h,A2h,ABh) (see #1334)
SeeAlso: #1313,#1331

(Table 1315)
Call the XMS driver "Move extended memory block" function with:
	AH = 0Bh
	DS:SI -> EMM structure (see #1335)
Return: AX = status
	    0001h success
	    0000h failure
		BL = error code (80h-82h,A3h-A9h) (see #1334)
Note:	if either handle in the EMM structure is 0000h, the corresponding
	  offset is considered to be an absolute segment:offset address in
	  directly addressable memory

(Table 1316)
Call the XMS driver "Lock extended memory block" function with:
	AH = 0Ch
	DX = handle of block to lock
Return: AX = status
	    0001h success
		DX:BX = 32-bit linear address of locked block
	    0000h failure
		BL = error code (80h,81h,A2h,ACh,ADh) (see #1334)
Note:	MS Windows 3.x rejects this function for handles allocated after
	  Windows started

(Table 1317)
Call the XMS driver "Unlock extended memory block" function with:
	AH = 0Dh
	DX = handle of block to unlock
Return: AX = status
	    0001h success
	    0000h failure
		BL = error code (80h,81h,A2h,AAh) (see #1334)

(Table 1318)
Call the XMS driver "Get handle information" function with:
	AH = 0Eh
	DX = handle for which to get info
Return: AX = status
	    0001h success
		BH = block's lock count
		BL = number of free handles left
		DX = block size in KB
	    0000h failure
		BL = error code (80h,81h,A2h) (see #1334)
BUG:	MS Windows 3.10 acts as though unallocated handles are in use
Note:	MS Windows 3.00 has problems with this call

(Table 1319)
Call the XMS driver "Reallocate extended memory block" function with:
	AH = 0Fh
	DX = handle of block
	BX = new size of block in KB
Return: AX = status
	    0001h success
	    0000h failure
		BL = error code (80h,81h,A0h-A2h,ABh) (see #1334)

(Table 1320)
Call the XMS driver "Request upper memory block" function with:
	AH = 10h
	DX = size of block in paragraphs
Return: AX = status
	    0001h success
		BX = segment address of UMB
		DX = actual size of block
	    0000h failure
		BL = error code (80h,B0h,B1h) (see #1334)
		DX = largest available block
Notes:	Upper Memory consists of non-EMS memory between 640K and 1024K
	the XMS driver need not implement functions 10h through 12h to be
	  considered compliant with the standard

(Table 1321)
Call the XMS driver "Release upper memory block" function with:
	AH = 11h
	DX = segment address of UMB to release
Return: AX = status
	    0001h success
	    0000h failure
		BL = error code (80h,B2h) (see #1334)
Note:	the XMS driver need not implement functions 10h through 12h to be
	  considered compliant with the standard

(Table 1322)
Call the XMS v3.0+ driver "Reallocate upper memory block" function with:
	AH = 12h
	DX = segment address of UMB to resize
	BX = new size of block in paragraphs
Return: AX = status
	    0001h success
	    0000h failure
		BL = error code (80h,B0h,B2h) (see #1334)
		DX = maximum available size (RM386)
Note:	the XMS driver need not implement functions 10h through 12h to be
	  considered compliant with the standard

(Table 1323)
Call the QEMM v5.11 "???" function with:
	AH = 34h  (QEMM 5.11 only, undocumented)
	???
Return: ???

(Table 1324)
Call the QEMM v5.11 "???" function with:
	AH = 44h  (QEMM 5.11 only, undocumented)
	???
Return: ???

(Table 1325)
Call the Netroom RM386 v6.00 "Reallocate upper memory block" function with:
	AH = 80h
	DX = segment address of UMB to resize
	BX = new size of block in paragraphs
Return: AX = status
	    0001h success
	    0000h failure
		BL = error code (80h,B0h,B2h) (see #1334)
		DX = maximum available size
Note:	this function is identical to function 12h

(Table 1326)
Call the Netroom RM386 v6.00 "re-enable HMA allocation" function with:
	AH = 81h
Return: AX = 0001h (success)

(Table 1327)
Call the Netroom RM386 v6.00 "Cloaking API" function with:
	AH = 82h
	DX = XMS handle of block containing protected-mode code
	CL = code size (00h 16-bit, else 32-bit)
	ESI, EDI = parameters to pass to protected-mode code
Return: AX = status
	    0001h success
	    0000h failed
		BL = error code (A2h,B0h) (see #1334)
Note:	this function calls offset 0 in the XMS memory block with
	    EBX = physical address of block's start
	    CS = code selector for XMS block at EBX (16-bit or 32-bit)
	    DS = data selector for XMS block, starting at EBX
	    ES = selector for V86 memory access to full real-mode 1088K
	    GS = selector for full flat address space
	    ESI, EDI from V86 mode

(Table 1328)
Call the Netroom RM386 v6.00 "Create new UMB entry" function with:
	AH = 83h
	BX = segment of high-memory block
	DX = first page of start of block
	CX = number of consecutive pages in block
	DI = start of UMB in block
Return: AX = 0001h (success)
	DI = segment of first high-DOS block
Note:	the new UMB is not linked into the high-memory chain

(Table 1329)
Call the Netroom RM386 v6.00 "Get all XMS handles info" function with:
	AH = 84h
	CX = size of buffer for handle info
	ES:DI -> buffer for handle info (see #1336)
Return: AX = 0001h (success)
	DX = current number of allocated XMS handles

(Table 1330)
Call the XMS v3.0 driver "Query free extended memory" function with:
	AH = 88h
Return: EAX = largest block of extended memory, in KB
	BL = status (00h,80h,81h,A0h) (see #1334)
	ECX = physical address of highest byte of memory
	    (valid even on error codes 81h and A0h)
	EDX = total Kbytes of extended memory (0 if status A0h)
BUG:	HIMEM v3.03-3.07 crash on an 80286 machine if any of the 8Xh functions
	  are called
SeeAlso: #1312,#1331

(Table 1331)
Call the XMS v3.0 driver "Allocate any extended memory" function with:
	AH = 89h
	EDX = Kbytes needed
Return: AX = status
	    0001h success
		DX = handle for allocated block (free with AH=0Ah) (see #1314)
	    0000h failure
		BL = status (80h,81h,A0h,A1h,A2h) (see #1334)
SeeAlso: #1313,#1330

(Table 1332)
Call the XMS v3.0 driver "Get extended EMB handle information" function with:
	AH = 8Eh
	DX = handle
Return: AX = status
	    0001h success
		BH = block's lock count
		CX = number of free handles left
		EDX = block size in KB
	    0000h failure
		BL = status (80h,81h,A2h) (see #1334)
BUG:	MS-DOS 6.0 HIMEM.SYS leaves CX unchanged

(Table 1333)
Call the XMS v3.0 driver "Reallocate any extended memory block" function with:
	AH = 8Fh
	DX = unlocked handle
	EBX = new size in KB
Return: AX = status
	    0001h success
	    0000h failure
		BL = status (80h,81h,A0h-A2h,ABh) (see #1334)
BUG:	HIMEM v3.03-3.07 crash on an 80286 machine if any of the 8Xh functions
	  are called

(Table 1334)
Values for XMS error code returned in BL:
 00h	successful
 80h	function not implemented
 81h	Vdisk was detected
 82h	an A20 error occurred
 8Eh	a general driver error
 8Fh	unrecoverable driver error
 90h	HMA does not exist or is not managed by XMS provider
 91h	HMA is already in use
 92h	DX is less than the /HMAMIN= parameter
 93h	HMA is not allocated
 94h	A20 line still enabled
 A0h	all extended memory is allocated
 A1h	all available extended memory handles are allocated
 A2h	invalid handle
 A3h	source handle is invalid
 A4h	source offset is invalid
 A5h	destination handle is invalid
 A6h	destination offset is invalid
 A7h	length is invalid
 A8h	move has an invalid overlap
 A9h	parity error occurred
 AAh	block is not locked
 ABh	block is locked
 ACh	block lock count overflowed
 ADh	lock failed
 B0h	only a smaller UMB is available
 B1h	no UMB's are available
 B2h	UMB segment number is invalid

Format of EMM structure:
Offset	Size	Description	(Table 1335)
 00h	DWORD	number of bytes to move (must be even)
 04h	WORD	source handle
 06h	DWORD	offset into source block
 0Ah	WORD	destination handle
 0Ch	DWORD	offset into destination block
Notes:	if source and destination overlap, only forward moves (source base
	  less than destination base) are guaranteed to work properly
	if either handle is zero, the corresponding offset is interpreted
	  as a real-mode address referring to memory directly addressable
	  by the processor

Format of XMS handle info [array]:
Offset	Size	Description	(Table 1336)
 00h	BYTE	handle
 01h	BYTE	lock count
 02h	DWORD	handle size
 06h	DWORD	handle physical address (only valid if lock count nonzero)
SeeAlso: #1301
--------m-2F4320-----------------------------
INT 2F U - HIMEM.SYS - Mach 20 SUPPORT
	AX = 4320h
	???
Return: ???
--------m-2F4330-----------------------------
INT 2F CU - HIMEM.SYS v2.77+ - GET EXTERNAL A20 HANDLER ADDRESS
	AX = 4330h
Return: AL = 80h if external A20 handler provided
	    ES:BX -> external A20 handler (see #1337)
	    CL = A20 detection support
		00h handler is unable to report A20 state
		01h handler supports function 0002h to report A20 state
Note:	HIMEM.SYS calls this function to allow an external program to provide
	  an A20 handler (i.e. to support a machine not supported by HIMEM
	  itself)
SeeAlso: AX=4308h,AX=4310h

(Table 1337)
Call parameters for external A20 handler are:
	AX = function
	    0000h disable A20
	    0001h enable A20
	    0002h get A20 state
Return: AX = status (functions 0000h and 0001h)
	    0000h failure
	    0001h successful
	AX = A20 state (function 0002h)
	    0000h disabled
	    0001h enabled
Note:	HIMEM.SYS only calls function 0002h if the returned CL indicated that
	  the handler supports the call