Title says it all. I've got a working Hello World boot sector, now I want to make it load some more sectors but I don't know which memory is safe to overwrite...

0000:0000 - 0040:0000 = Interrupt Table (don't put code here)
0040:0000 - 0050:0000 = Bios Communication area(don't put code here)
0050:0000- 9000:FFFF = Data Area (Every thing here is free to put code)
07C0:0000 - 07c0:0200 = Boot up code(this is where your bootsector code is when you boot) it is also equal to 0000:7c00 - 0000:7e00
A000:0000 - FFFF:0010 = Video, option roms, BIOS (don't attempt to put code here, you WILL crash; there are parts you can write to however...)
A000:0000 - A000:FFFF = Video screen in graphical mode(put only screen pixel data here)
B800:0000 - B800:FFFF = Video screen in text mode(put only screen char data here)

This is your realmode memory map in the most basic form i can give during my short lunch break. When i get home from work, again, i will find you a more detailed resource.

Once you start using extended memory, you'll want to query the BIOS for special things like reserved addresses and memory holes... I can't remember the INTs for this, but it's probably documented somewhere easy to find - if all else fails, check linux kernel ^_^

@asmdemon: Thanks!

@f0dder:
Well, that's a little over my head: I'm used to real mode asm. So I don't know much about the tables you have to set up and everything else you need to do before switching to pmode - it's a little intimidating (real mode is so much simpler)... any good tutorials on that, BTW?

Well, if you stay with real mode code for a bit, and go with one of the standard memory maps, you should be safe I think. As for protected mode setup... this takes a bit of work I'd suggest the intel systems programming manual (vol.3 of their IA32 docs, iirc), www.osdev.org, http://www.nondot.org/sabre/os/articles - that should get you (more than) started

wow, sweet link! Thanks!