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Asked: 2026-06-04T07:16:47+00:00

Why doesn’t NASM compile to an object file with the org directive? org 0x7C00

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Why doesn’t NASM compile to an object file with the org directive?

org 0x7C00
nop
mov ax, ax
nop

If I compile this with:

nasm -O0 -fobj temp.asm

NASM gives me an error for whatever reason:

temp.asm:1: error: parser: instruction expected
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1 Answer

  1. Editorial Team

    In this case instead of org you should use resb:

    ; file: nasmOrg.asm
; assemble: nasm -f obj nasmOrg.asm -o nasmOrg.obj

SEGMENT _TEXT PUBLIC CLASS=CODE USE16

;        resb    0x0100 ; reserve 0x0100 bytes for a .COM program
        resb    0x7C00 ; reserve 0x7C00 bytes for a boot sector
..start:
nop
mov ax, ax
nop

    This is how you can compile different parts of a .COM program into separate object files. If you use TLINK as the linker, the next step would be:

    tlink.exe /t nasmOrg.obj [any other object files], nasmOrg.bin

    Note that if you omit the comma and the following name of the resultant binary (nasmOrg.bin) or if you specify a name with the .COM extension (e.g. nasmOrg.com), TLINK will refuse to link, it will say something like:

    Error: Cannot generate COM file : invalid initial entry point address

    And you’ll have to change 0x7C00 to 0x0100 to make a .COM program.

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