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Real mode assembly I: Difference between revisions
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{{Warning|Please see the [[Real Mode OS Warning]] page before continuing.}}
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== Overview ==
You're probably going to sigh and dismiss yet ''another'' tutorial on writing operating systems in [[x86]] assembly language, especially since this one uses real mode. But there's a catch to this one; it actually does more than printing "Hello World" to the screen and halting.
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== So what's it going to look like? ==
Well, there will be a single source file, the kernel. What about a [[bootloader]]? This is such a small kernel, we're not going to use a filesystem at all, we're just going to put the kernel into the first few sectors of the
The system will have a string printing call (of course), keyboard input, and a strcmp call similar to that of C, all packaged into less than a sector.
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Here you go, go wild.
<
org 0x7C00 ; add 0x7C00 to label addresses
mov ax, 0 ; set up segments
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mov es, ax
mov ss, ax ; setup stack
mov sp,
mov si, welcome
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times 510-($-$$) db 0
dw 0AA55h ; some BIOSes require this signature
</syntaxhighlight>
To assemble on Windows:
<
nasm kernel.asm -f bin -o kernel.bin
partcopy kernel.bin 0 200 -f0
</syntaxhighlight>
Or on Linux:
<
nasm kernel.asm -f bin -o kernel.bin
dd if=kernel.bin of=/dev/
</syntaxhighlight>
Those commands assemble your kernel binary and write them to the first
== What next? ==
Why, that's up to you of course! You could add more commands, expand your OS to another sector and learn to use the BIOS
Have fun with your OS, however you decide to write it!
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'''EDIT on December 12 2008: I've written a second part to this tutorial at [[Real mode assembly II]]. This and future parts will have less code to copy and paste and more theory!'''
[[Category:Assembly]]
[[Category:Real mode assembly]]
<- none | [[Real mode assembly II]] ->
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