OSDev.org

Posted: **Tue Dec 25, 2007 9:00 pm**

how do i write files to certain sectors of a floppy? like grub and the kernel and stuff? I know bootloaders must go on cyl 0 head 0 sec 1, how do i write a file to that? like the prog in emu8086, only to a real floppy.

thanks

Posted: **Tue Dec 25, 2007 11:26 pm**

Let's think this though...

A sector is 512 bytes, 1 sector is used... so you have 2879 sectors available...

Instead of troubling yourself with such basic math.. consider a file system..

(If you want to know how to actually write bytes to a floppy image.. use your favourite programming languages file I/O routines..)

Posted: **Tue Dec 25, 2007 11:35 pm**

but how do you write to the boot sector?

Posted: **Wed Dec 26, 2007 5:46 am**

here is a sample "read disk" code.
Just replace INT 13 AH=02 with INT 13 AH=03 to make it a "Write disk" code.
Also consider the following page for reference http://www.ctyme.com/intr/rb-0608.htm

Code: Select all


    PUSH CS
    POP DS
    MOV CX,5
    XOR AH,AH
.Reset_disk
    INT 13
    JNC .Read_disk
    LOOP .Reset_disk   ; retry for 5 times
    ; Print a reset error message
    MOV SI, ResetErrorMsg
    CALL PrintStr         ; print the error message
    JMP .Stop
.Read_disk
    MOV AH,02
    MOV AL,SectNumber
    MOV BX,Stage2Address
    MOV CX,0001     ; read from cylinder #1
    XOR DX,DX        ; Read from floppy (Disk 0)
    INT 13
    JNC .RunStage2
    MOV SI,ReadFailMsg
    CALL PrintStr     ; Print the read error message
.Stop
    HLT
.RunStage2
    JMP Stage2Address
.PrintStr
    PUSH BX
    PUSH AX
    MOV AH,0E
    MOV BX,0007
    LODSB
.RdChr
    JZ .EndStr
    INT 10
    JMP .RdChr
.EndStr
    POP AX
    POP BX
    RET

OSDev.org

Write to certain sectors of floppy

Write to certain sectors of floppy