I think you mean the "boot sector", which is one 2048-byte sector on the CD, not accessible as a file. It's loaded into memory and executed by the BIOS when the CD is booted, and it loads SETUPLDR.BIN from the I386 directory and executes that.Hard disks (or emulated USB drives) have 512-byte sectors and use FAT16/32 filesystems, while CD-ROMs have 2048-byte sectors and use the ISO-9660 filesystem. The standard boot sector on the CD is written to understand ISO9660 FS, while hard disk boot sectors understand FAT16/32. However, it is possible to perform the same function, namely loading SETUPLDR.BIN from I386 directory. You're going to have to write your own boot sector to do that... and do it in less than 512 bytes. Oh yes, that's what I want. But I don't know how to do it.