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Hello World

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Structure:
.zeroTerminated:

--- Code: ---times 512-($-$$) db 0
jmp start

print:
 pusha
 .printloop:
   mov al, [si]
   cmp al, 0
   jne .printchar
   popa
   ret
 .printchar:
   mov ah, 0x0e
   int 0x10
   add si, 1
   jmp .printloop
ret

string: db "Hello World.", 0

start:
  mov si, string
  call print

--- End code ---

debs3759:

--- Quote from: Structure on December 11, 2019, 04:03:35 PM ---.zeroTerminated:

--- Code: ---times 512-($-$$) db 0
jmp start

print:
 pusha
 .printloop:
   mov al, [si]
   cmp al, 0
   jne .printchar
   popa
   ret
 .printchar:
   mov ah, 0x0e
   int 0x10
   add si, 1
   jmp .printloop
ret

string: db "Hello World.", 0

start:
  mov si, string
  call print

--- End code ---

--- End quote ---

In your code, if that is the entire code, $ = $$ (both are at the start of your code). So

times 512-($-$$) db 0

inserts 512 0 bytes at the start of the code. What is that for?

Structure:
The first 512 kb are reserved for the boot sector:

https://en.wikipedia.org/wiki/Boot_sector

or a file header, etc...

debs3759:
I did wonder if this was related to a boot sector, but it wasn't obvious from your code. My FAT12 boot sector code is lower down in this forum :)

T145:
You don't need any of that bootcode, since you're not making anything to boot into, like a virtual floppy disk. As you know, in 16 bit land we just start executing from the top, so you can always just use the following macro to print your string:


--- Code: ---%macro puts 1
    pushaw
    mov     si, %1
    mov     ah, 0Eh    ; INT 10h doesn't trash ah or bx
    mov     bx, 7      ; video mode support
%%read:
    lodsb
    test    al, al     ; check for null-terminating character (0)
    jz      %%done
    int     10h        ; print character in al
    jmp     %%read
%%done:
    popaw
%endmacro

--- End code ---

Then just `puts string` and either `ret` or `jmp $` to avoid running into the data section.

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