Babystep1: Difference between revisions

The CPU starts in real mode and the BIOS loads this code at address 0000:7c00. The "times 512..." stuff 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 Partcopy 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 once 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 try 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.