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Int 19 - System - Bootstrap Loader [B]
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. 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 below). 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
See Also: INT 14/AH=17h,INT 18
Format of VDISK header block (at beginning of INT 19 handler's segment):
Offset Size Description
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
00h 446 BYTEs Master bootstrap loader code
1BEh 16 BYTEs partition record for partition 1 (see below)
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
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 below)
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
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
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 (planned)
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
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