DOS6.0 source program of the hard disk boot record source program Fdboot.asm

;/*
; * Microsoft Confidential
; * Copyright (C) Microsoft Corporation 1983-1991
; * All Rights Reserved.
; */
; BOOT-IBM hard disk boot record 6/8/82
;
;
; This is the standard boot record, that'll be shipped on all hard disks. It contains:
;
; 1. Code to load (and give control to) the boot record for 1 of 4 possible
; Operating systems.
;
; 2. A partition table at the "End of" The boot record, followed by the required signature.
;
;
_data Segment Public
Assume Cs:_data,ds:_data
ORG 600h

CLI; no interrupts for now
XOR Ax,ax
MOV Ss,ax
mov sp,7c00h new stack at 0:7C00
mov si,sp; where this boot record starts-0:7c00
Push AX
Pop es; seg regs the same
Push AX
Pop ds
STI; interrupts OK now
Cld
mov di,0600h; Where to relocate the This boot record to
MOV cx,100h
REPNZ MOVSW relocate to 0:0600
; JMP Entry2
DB 0eah
DW $+4,0
Entry2:
mov si,offset tab;p artition table
MOV bl,4 number of table entries
Next
CMP byte ptr[si],80h is this a bootable entry?
JE Boot; yes
CMP byte ptr[si],0 No, is boot indicator zero?
Jne bad; No, it must being X "or" x "to be valid
Add si,16 Yes, go to next entry
Dec BL
JNZ Next
int 18h; no bootable entries-go to ROM basic
Boot
mov Dx,[si]; head and drive to boot
mov cx,[si+2]; cyl, sector to boot from
MOV Bp,si Save table entry to the partition boot record
NEXT1:
Add si,16 Next Table entry
Dec BL; # entries Left
JZ Tabok entries look OK
CMP byte ptr[si],0 All remaining entries should begin with zero
Je next1; this one is OK
Bad
MOV si,offset M1 oops-found a Non-zero entry-the table is bad
Msg
LODSB get a message character
CMP al,0
Je hold
Push SI
MOV bx,7
MOV ah,14
int 10h; display it
Pop si
JMP msg;d o the entire message
;
HOLD:JMP hold spin here-nothing more Todo
Tabok:
mov di,5; retry count
Rdboot:
mov bx,7c00h; Where to read system boot record
MOV ax,0201h read 1 sector
Push di
int 13h; Get the boot record
Pop di
Jnc goboot; Successful-now Give it control
XOR Ax,ax; Had an error, so
int 13h; recalibrate
Dec di; Reduce retry count
JNZ rdboot If retry count above zero, go retry
mov si,offset m2 all retries done-permanent error-point to message,
JMP msg; go display message and loop
Goboot:
mov si,offset m3;p repare for invalid boot record
MOV Di,07dfeh
CMP word ptr [di],0aa55h;d oes the boot record have the
; Required signature?
Jne msg; No, display invalid system boot record message
MOV si,bp Yes, pass partition table entry address
DB 0eah
DW 7c00h,0

Include FDISK5.CL1

ORG 7beh
tab:;p artition table
DW 0,0;p artition 1 begin
DW 0,0;p artition 1 End
DW 0,0;p artition 1 relative sector (low, high parts)
DW 0,0;p artition 1 # of sectors (low, high parts)
DW 0,0;p artition 2 begin
DW 0,0;p artition 2 End
DW 0,0;p artition 2 relative sector
DW 0,0;p artition 2 # of Sectors
DW 0,0;p artition 3 begin
DW 0,0;p artition 3 End
DW 0,0;p artition 3 Relative sector
DW 0,0;p artition 3 # of Sectors
DW 0,0;p artition 4 begin
DW 0,0;p artition 4 End
DW 0,0;p artition 4 Relative sector
DW 0,0;p artition 4 # of Sectors
Signa db 55h,0aah; signature

_data ends
End