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hi, i just read a bit about making a boot disk. as i understand it: all i need is that 0AA55h at the end of the 512 bytes. so i have written the code below which is supposed to draw a pixel on the screen but all i get is a flickering screen. do i need to do something else essencial??

model tiny
.386
.code
        org 100h
main:
        mov     ax,13h
        int     10h

        mov     ax,0a000h
        mov     es,ax

        mov     bx,320*100+160
        mov     al,15

        mov     es:[bx],al
inf:
        jmp inf-100h

        org 512+100h

        dw 0AA55h
end     main

>> as i understand it: all i need is that 0AA55h at the end of the 512 bytes

Not exactly, some BIOSes need a short jump followed by a nop at the beginning. Different BIOSes may or may not setup your stack. My boot sector would start like this(nasm syntax):

[BITS 16]
[ORG 0]
jmp short Start
nop

Start:
mov ax,0x07c0
mov ds,ax
mov es,ax
xor ax,ax
mov ss,ax
mov sp,0x7c00

jmp short $

times 510-($-$$) db 0
dw 0xAA55

It could also be that your video card doesn't provide the BIOS service routine to set to 320x200x256 but that'd be a little odd. Also note that the ORG is 0, an ORG of 0x100 is for DOS com programs.

yes that org 100h is needed by the linker "tlink", it doesnt accept anything else and gives errors. when i use jumps i just jump at:

label:
jmp label-100h

because i assume that the bios loads the code at 0000h anyways. i think org is just relevant for the labels.
but i will try that "jmp-start-nop" thingy, thank you very much.

ok i downloaded nasm now and got the code to work... thank you very much for your help!