INT 21 - Stacker - GET DEVICE DRIVER ADDRESS AND SET VOLUME NUMBER              
	AX = 4404h
	BL = drive number (00h = default, 01h = A:, etc.)
	CX = 0004h
	DS:DX -> DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address. buffer to receive device driver address
Return: buffer filled with pointer into Stacker device driver (see #02550):
	  driver + 19h if Stacker Anywhere controls this drive
	  driver + 1Ah if Stacker controls this drive
	  unchanged else
Notes:	in addition to returning the address of the Stacker device driver,
	  this call also sets the volume number at offset 58h in the device
	  driver (see #02550 at INT 25/AX=CDCDh)
	Stacker Anywhere does not link its built-in device driver into
	  the standard device driver chain, but it can be found via CDSsee Current Directory Structure/DPBsee Drive Paramter Block
	this call can be used as an installation check for all versions of
	  Stacker and Stacker Anywhere to avoid the INT 25 call
SeeAlso: AX=4408h,AX=440Eh,AH=52h,INT 25/AX=CDCDh
                                                                                

INT 21 - Stacker - GET STACVOL FILE SECTORS                                     
	AX = 4404h
	BL = drive number (0 is current drive)
	CX = byte count (i.e., 200h = 1 sector)
	DS:DX -> buffer (see #01529)
Return: Data Buffer contains the number of sectors requested from the
	  STACVOL physical file for the drive specified.


Format of Stacker buffer:
Offset	Size	Description	(Table 01529)
 00h	WORD	01CDh
 02h	WORD	sector count
 04h	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	number of starting sector
 08h	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	far pointer to Data Buffer
                                                                                

INT 21 - DUBLDISK.SYS v2.6 - GET INFO                                           
	AX = 4404h
	BL = drive number of DoubleDisk drive (00h = default, 01h = A:, etc.)
	CX = number of bytes (000Ah-0014h, call ignored otherwise)
	DS:DX -> data record (see #01530)
Return: CF clear if successful
	    AX = number of bytes read
	CF set on error
	    AX = error code (01h,05h,06h,0Dh) (see #01680 at AH=59h/BX=0000h)
Program: DUBLDISK.SYS is the device driver portion of DoubleDisk, a disk
	  expander by Vertisoft Systems, Inc.
InstallCheck:	for v2.6, scan memory for the signature "FATsee File Allocation Table 2.6  byte:",
	  which is immediately followed by a data table (see #01531)
BUG:	VOPT (a disk optimizer by Golden Bow Software) assumes that any driver
	  which returns the "correct" number of bytes when the first word of
	  the buffer for the data record contains the signature value 4444h is
	  DoubleDisk; a workaround is for the non-DoubleDisk driver to return
	  no data if the signature is present
SeeAlso: AX=440Dh"DOS 3.2+"
Index:	installation check;DUBLDISK.SYS


Format of DUBLDISK data record:
Offset	Size	Description	(Table 01530)
 00h	WORD	(call) signature 4444h
 02h	BYTE	(call) function
			00h ???
			01h ???
---function 00h---
 02h	BYTE	(ret) ???
 03h	BYTE	(ret) ???
---function 01h---
 02h	WORD	(ret) 4444h
 04h	WORD	allocation unit size???
 06h	WORD	???
 08h	WORD	???
 0Ah	BYTE	???


Format of DUBLDISK signature data table:
Offset	Size	Description	(Table 01531)
 00h  5 BYTEs	???
 05h	BYTE	first drive number
 06h	BYTE	number of drives
 07h	???
                                                                                

INT 21 - DBLSPACE.BIN - IOCTL - FLUSH OR INVALIDATE INTERNAL CACHES             
	AX = 4404h
	BL = drive number (00h = default, 01h = A:, etc)
	CX = 000Ah (size of DSPACKET structure)
	DS:DX -> DSPACKET structure (see #01532)
Return: CF clear if IOCTL successful -- check DSPACKET for actual status
	    AX = number of bytes actually transferred
	CF set on error
	    AX = error code (01h,05h,06h,0Dh) (see #01680 at AH=59h/BX=0000h)
SeeAlso: AX=4405h"DBLSPACE",INT 2F/AX=4A11h/BX=0000h


Format of DoubleSpace DSPACKET structure:
Offset	Size	Description	(Table 01532)
 00h	WORD	signature 444Dh ("DM")
 02h	BYTE	command code
		46h ('F') flush internal caches
		49h ('I') flush and invalidate internal caches
 03h	WORD	result code
		(ret) 4F4Bh ("OK") if successful, else unchanged
 05h  5 BYTEs	padding
                                                                                

INT 21 - DBLSPACE.BIN v6.2 - IOCTL - GET ??? FOR SPECIFIED DRIVE                
	AX = 4404h
	BL = drive number (00h = default, 01h = A:, etc)
	CX = size of DSPACKET structure (ignored in DOS 6.2)
	DS:DX -> DSPACKET structure (see #01533)
Return: CF clear if IOCTL successful -- check DSPACKET for actual status
	    AX = number of bytes actually transferred
	CF set on error
	    AX = error code (01h,05h,06h,0Dh) (see #01680 at AH=59h/BX=0000h)
SeeAlso: AX=4405h"DBLSPACE",INT 2F/AX=4A11h/BX=0000h


Format of DoubleSpace DSPACKET structure:
Offset	Size	Description	(Table 01533)
 00h	WORD	signature 444Dh ("DM")
 02h	BYTE	command code
		53h ('S') get ??? for specified drive
 03h	WORD	result code
		(ret) 4F4Bh ("OK") if successful, else unchanged
 05h	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	(ret) pointer to 96-byte ??? data
 09h	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	(ret) pointer to ??? data
 0Dh  3 BYTEs	reserved
                                                                                

INT 21 U - DoubleTools v1.0 - GET ???                                           
	AX = 4404h
	BL = drive number (00h = default, 01h = A:, etc)
	CX = 0006h
	DS:DX -> DoubleTools structure (see #01534)
Return: CF clear if IOCTL successful -- check DSPACKET for actual status
	    AX = number of bytes actually transferred
	CF set on error
	    AX = error code (01h,05h,06h,0Dh) (see #01680 at AH=59h/BX=0000h)
Note:	the Transporter device driver has the signature 55h 61h 50h 74h
	  ("DaPt") twelve bytes after it beginning


Format of DoubleTools structure:
Offset	Size	Description	(Table 01534)
 00h	WORD	(call) signature 55h AAh
		(ret) signature 78h 70h ("xp")
 02h	WORD	(call) signature 52h 16h
		(ret) ???
 04h	WORD	(ret) segment of driver's DS (same as its PSPsee Program Segment Prefix)