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Copyright 1991 David Jurgens |
Warm Boot / System Bootstrap
- Ctrl-Alt-Delete results in a warm boot but only after part of the
POST sequence has executed. See COLD BOOT for more information.
- ROM BIOS bootstrap loader (INT 19) attempts Boot Record load
- Drive A: is searched for a Boot Record, if no Boot Record is found
the active partition of the first drive is searched. If found, it
is loaded into memory at 7C00:0 and given control. If still not
found Cassette BASIC is loaded (IBM only) or a prompt for a system
diskette is displayed.
- the boot record code checks that IBMBIO.COM and IBMDOS.COM (IO.SYS
and DOS.SYS for MSDOS) exist and are the first two files. These
files must be contiguous and the first two directory entries.
- boot record loads IBMBIO.COM
- IBMBIO.COM initialization code loads IBMDOS.COM
∙ determines equipment status
∙ resets disk system
∙ initializes attached devices
∙ loads installable device drivers
∙ sets DOS relative interrupt vectors
∙ relocates IBMDOS.COM downward and begins its execution
- IBMDOS.COM initializes its working tables
∙ initializes DOS interrupt vectors for interrupts 20h through 27h
∙ builds PSP for COMMAND.COM at lowest possible segment
∙ interrupt vectors for INTs 0Fh through 3Fh are initialized
(for DOS 3.1+)
∙ loads COMMAND.COM (or specified command interpreter) using the
EXEC call.
- AUTOEXEC.BAT is then loaded and executed
- see BOOT RECORD COLD BOOT
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| Esc or Alt-X to exit |
warm boot |
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