Back up the hard disk master boot partition into a file _dos/bat

C:\dos>debug
-a100
1078:0100 mov ax,0201; 02 = Read, 01 = number of Sectors Read
1078:0103 mov bx,0200; After reading, place in memory at 0200
1078:0106 mov cx,0001; 00 = Track number, 01 = Start Sector Area code
1078:0109 mov dx,0080; 00 = 0 Head, 80 for hard disk
1078:010c INT 13; BIOS Disk Outage
1078:010e int 20; End
1078:0110 ^c
-g=100; Executed from 0100
program terminated normally; Program Display
-RCX; CX registers define the size of the saved file
CX 0000; Set File size
: 300; 300H = 768 bytes
-N Mainboot.dat; Save in file Mainboot.dat
-W; Write a file
Writing 00300 bytes; Program Display
     -q                                  ;  Exit  DEBUG