INT 19 - SYSTEM - BOOTSTRAP LOADER
Desc:	This interrupt reboots the system without clearing memory or restoring
	  interrupt vectors.  Because interrupt vectors are preserved, this
	  interrupt usually causes a system hang if any TSRs have hooked
	  vectors from 00h through 1Ch, particularly INT 08.
Notes:	Usually, the BIOS will try to read sector 1, head 0, track 0 from drive
	  A: to 0000h:7C00h.  If this fails, and a hard disk is installed, the
	  BIOS will read sector 1, head 0, track 0 of the first hard disk.
	  This sector should contain a master bootstrap loader and a partition
	  table (see #0455).  After loading the master boot sector at
	  0000h:7C00h, the master bootstrap loader is given control.  It will
	  scan the partition table for an active partition, and will then load
	  the operating system's bootstrap loader (contained in the first
	  sector of the active partition) and give it control.
	true IBM PCs and most clones issue an INT 18 if neither floppy nor hard
	  disk have a valid boot sector
	to accomplish a warm boot equivalent to Ctrl-Alt-Del, store 1234h in
	  0040h:0072h and jump to FFFFh:0000h.	For a cold boot equivalent to
	  a reset, store 0000h at 0040h:0072h before jumping.
	VDISK.SYS hooks this interrupt to allow applications to find out how
	  much extended memory has been used by VDISKs (see #0454).  DOS 3.3+
	  PRINT hooks INT 19 but does not set up a correct VDISK header block
	  at the beginning of its INT 19 handler segment, thus causing some
	  programs to overwrite extended memory which is already in use.
	the default handler is at F000h:E6F2h for 100% compatible BIOSes
	MS-DOS 3.2+ hangs on booting (even from floppy) if the hard disk
	  contains extended partitions which point at each other in a loop,
	  since it will never find the end of the linked list of extended
	  partitions
	under Windows Real and Enhanced modes, calling INT 19 will hang the
	  system in the same was as under bare DOS; under Windows Standard
	  mode, INT 19 will successfully perform a cold reboot as it appears
	  to have been redirected to a MOV AL,0FEh/OUT 64h,AL sequence
SeeAlso: INT 14/AH=17h,INT 18,INT 5B"PC Cluster"

Format of VDISK header block (at beginning of INT 19 handler's segment):
Offset	Size	Description	(Table 0454)
 00h 18 BYTEs	n/a (for VDISK.SYS, the device driver header)
 12h 11 BYTEs	signature string "VDISK	 Vn.m" for VDISK.SYS version n.m
 1Dh 15 BYTEs	n/a
 2Ch  3 BYTEs	linear address of first byte of available extended memory

Format of hard disk master boot sector:
Offset	Size	Description	(Table 0455)
 00h 446 BYTEs	Master bootstrap loader code
1BEh 16 BYTEs	partition record for partition 1 (see #0456)
1CEh 16 BYTEs	partition record for partition 2
1DEh 16 BYTEs	partition record for partition 3
1EEh 16 BYTEs	partition record for partition 4
1FEh	WORD	signature, AA55h indicates valid boot block

Format of partition record:
Offset	Size	Description	(Table 0456)
 00h	BYTE	boot indicator (80h = active partition)
 01h	BYTE	partition start head
 02h	BYTE	partition start sector (bits 0-5)
 03h	BYTE	partition start track (bits 8,9 in bits 6,7 of sector)
 04h	BYTE	operating system indicator (see #0457)
 05h	BYTE	partition end head
 06h	BYTE	partition end sector (bits 0-5)
 07h	BYTE	partition end track (bits 8,9 in bits 6,7 of sector)
 08h	DWORD	sectors preceding partition
 0Ch	DWORD	length of partition in sectors

(Table 0457)
Values for operating system indicator:
 00h	empty
 01h	DOS 12-bit FAT
 02h	XENIX root file system
 03h	XENIX /usr file system (obsolete)
 04h	DOS 16-bit FAT
 05h	DOS 3.3+ extended partition
 06h	DOS 3.31+ Large File System
 07h	QNX
 07h	OS/2 HPFS
 07h	Advanced Unix
 08h	AIX bootable partition, SplitDrive
 09h	AIX data partition
 09h	Coherent filesystem
 0Ah	OS/2 Boot Manager
 0Ah	OPUS
 0Ah	Coherent swap partition
 10h	OPUS
 12h	Compaq Diagnostics partition
 18h	AST special Windows swap file
 24h	NEC MS-DOS 3.x
 40h	VENIX 80286
 50h	Disk Manager, read-only partition
 51h	Disk Manager, read/write partition
 51h	Novell???
 52h	CP/M
 52h	Microport System V/386
 56h	GoldenBow VFeature
 61h	SpeedStor
 63h	Unix SysV/386, 386/ix
 63h	Mach, MtXinu BSD 4.3 on Mach
 63h	GNU HURD
 64h	Novell NetWare
 65h	Novell NetWare (3.11)
 70h	DiskSecure Multi-Boot
 75h	PC/IX
 80h	Minix v1.1 - 1.4a
 81h	Minix v1.4b+
 81h	Linux
 81h	Mitac Advanced Disk Manager
 82h	Linux Swap partition
 83h	Linux native file system (ext2fs/xiafs)
 84h	OS/2-renumbered type 04h partition (related to hiding DOS C: drive)
 93h	Amoeba file system
 94h	Amoeba bad block table
 B7h	BSDI file system (secondarily swap)
 B8h	BSDI swap partition (secondarily file system)
 C1h	DR-DOS 6.0 LOGIN.EXE-secured 12-bit FAT partition
 C4h	DR-DOS 6.0 LOGIN.EXE-secured 16-bit FAT partition
 C6h	DR-DOS 6.0 LOGIN.EXE-secured Huge partition
 DBh	CP/M, Concurrent CP/M, Concurrent DOS
 DBh	CTOS (Convergent Technologies OS)
 E1h	SpeedStor 12-bit FAT extended partition
 E4h	SpeedStor 16-bit FAT extended partition
 F2h	DOS 3.3+ secondary
 FEh	LANstep
 FFh	Xenix bad block table