Babystep1: Difference between revisions

The CPU starts in real mode and the [[BIOS]] loads this code at address 0000:7c00. The "times 512..."-($-$$) stuffdb 0" is NASM's way of saying fill up 512 bytes with zeros. And partcopy is going to expect that (200 in Hex = 512 in Decimal). Change it and you'll see Partcopypartcopy choke.

Often, you will see a so-called boot signature (0xAA55) at the end. Older versions of [[BIOS|BIOSes]] looked for this in order to identify a boot sector on a disk. It is evidently unnecessary nowadays. If it's needed, the last line would be replaced with (or some version of it):

But the thing I'd really like to point out is how onceOnce you've booted, and the cursor is happily blinking on a blank screen, you might notice two things. One is that the floppy motor will turn off and the other is that you can press Ctrl-Alt-Del to reboot. The point is that [[interrupts (such as INT 0x09)]] as still being generated.

For kicks tryTry clearing the interrupts flag:

The code is assembled in [[NASM]] and copied to floppy using partcopy, dd, or debug. Then you simply boot from the floppy.