Programming Forums - Question: Bootinit?

; This is a comment

[ORG 0x7C00];This just tells the program where it is in the memory. Not important

[BITS 16];Not important too.



jmp start        ; Jump over BIOS parameter block



start:;The label for the start of the actual program



push cs;Put cs onto the stack

pop ds;Take it out and put it into ds





mov si,Print_loading  ;Print loading message

call printstring ;Call is like jump, but it goes back. Like a function





   ;The complicated bit: Loads the next program

mov ah,02h       ;When ah=, int13 reads a disk sector

mov al,4          ;Al is how many sectors to read

mov ch,0          ;The track to read from

mov cl,2          ;Sector Id

mov dh,0          ;Head

mov dl,0          ;Drive (0 is floppy)

mov bx,0x1000         ;Es and Bx put together are where to load the program too (see jmp 0x1000:0x00)

mov es,bx

mov bx,0x00

int 13h  ;Int 13 is all functions for disks



mov si,putdot     ;Print a ".".

call printstring



jmp 0x1000:0x00    ;Run Bootinit from stack.



printstring:      ;Print string routine.

mov ah,0eh         ;Mov ah into 0, so int 10 prints

stringloop:         ;The following code loads each seperate charcter so it can be printed

lodsb          

cmp al,00         ;If al =0, then the string has all been loaded

je endstring

int 10h  ;When int 10 is called, and ah=, it prints

jmp stringloop

endstring:

ret          ;Ret returns







putdot    db '.',0

Print_loading db 13,10,'Loading Easy OS v0.01a...',0

times 425 db 0;wastes 425 bytes on purpose, so the sector is full (The program must be 512 bytes long)

I was looking at someone elses code, and right above printstring there is a jmp 0x1000:0x00. Why is it jumping there?

Here's the site: http://www.groovyweb.uklinux.net/index.php...your%20own%20os