hi folks, just did my first test with MASM and FASM with the same code (almos) and I falled in trouble. The only difference is that to produce just the 104 bytes I need to write to MBR in FASM I put org 7c00h and in MASM 0h.

The problem is on the

mov si, offset msg

that in the first case transletes it to 44 7C (7c44h) and with masm translates to 44 00 (0044h)! but just when I change org 7c00h to org 0h in MASM. Otherwise it will produce the entire segment from 0 to 7dff.

how do I solve it?

or in short, how to make MASM produce a binary that begins at 7c00h as it first byte and subsequent jumps remain relative to 7c00h?

.model TINY 
.code  
org             7c00h             ; Boot entry point. Address 07c0:0000 on the computer memory
 xor  ax, ax          ; Zero out ax
 mov  ds, ax       ; Set data segment to base of RAM
 jmp start       ; Jump to the first byte after DOS boot record data    

; ----------------------------------------------------------------------
; DOS boot record data
; ----------------------------------------------------------------------
brINT13Flag     db      90h             ; 0002h - 0EH for INT13 AH=42 READ
brOEM           db      'MSDOS5.0'      ; 0003h - OEM name & DOS version (8 chars)
brBPS           dw      512             ; 000Bh - Bytes/sector
brSPC           db      1               ; 000Dh - Sectors/cluster
brResCount      dw      1               ; 000Eh - Reserved (boot) sectors
brFATs          db      2               ; 0010h - FAT copies
brRootEntries   dw      0E0h            ; 0011h - Root directory entries
brSectorCount   dw      2880            ; 0013h - Sectors in volume, < 32MB
brMedia         db      240             ; 0015h - Media descriptor
brSPF           dw      9               ; 0016h - Sectors per FAT
brSPH           dw      18              ; 0018h - Sectors per track
brHPC           dw      2               ; 001Ah - Number of Heads
brHidden        dd      0               ; 001Ch - Hidden sectors
brSectors       dd      0               ; 0020h - Total number of sectors
                db      0               ; 0024h - Physical drive no.
                db      0               ; 0025h - Reserved (FAT32)
                db      29h             ; 0026h - Extended boot record sig
brSerialNum     dd      404418EAh       ; 0027h - Volume serial number (random)
brLabel         db      'OSAdventure'   ; 002Bh - Volume label  (11 chars)
brFSID          db      'FAT12   '      ; 0036h - File System ID (8 chars)

;------------------------------------------------------------------------
; Boot code
; ----------------------------------------------------------------------

start:
 mov si, offset msg
 call showmsg
hang: 
 jmp hang

msg    db  'Loading...',0

showmsg:
 lodsb
 cmp al, 0
 jz showmsgd
 push si
 mov bx, 0007
 mov ah, 0eh
 int 10h
 pop si
 jmp showmsg
showmsgd:
 retn

; ----------------------------------------------------------------------
; Boot record signature
; ----------------------------------------------------------------------
       dw   0AA55h                      ; Boot record signature
END