This looks a bit dubious for erasing a hard drive. INT 13h is the BIOS
diskette interrupt. This script appears to write random information to track 0, sector 1 of the floppy, the boot sector.
It might be the case that specifying the drive number (DL) as 80h might be an undocumented backdoor to 'fooling' the interrupt to write to the hard drive, but I've no info on this. Ordinarily, when using this interrupt, one would specify the drive number as 0 or 1, for drives A: or B: respectively.
Dell had me use that script to "reset" my harddrive when we were troubleshooting a bluescreen in WinXP. We were trying to eliminate the possibility of a boot virus, and this was the last ditch effort to clear the harddrive.
Turns out the problem was the CPU, but at least I learned something (a lot actually).