China DOS Union

The image of a hard disk is to copy each sector of the entire hard disk one by one in the order of sectors. That is to say, this file is a hard copy of the hard disk. Such a file is called an image file of the hard disk.

The concept of an ISO image of a CD is the same, which is a hard copy of all sectors of the CD.

The difference is that the beginning of a hard disk is the MBR sector and other related data structures, while the beginning of a CD has 32 K of 00 bytes, followed by other data structures unique to CDs. Therefore, the structures of hard disk images and CD images are also different.

Got a lot, thanks

To be honest, I personally think this technology is very groundbreaking, and I've been paying attention to it for a long time but there's been no result. If it can be realized, then optical drive discs will become less valuable. I can make all system discs (that is, discs that can boot the system) into ISO or BIN files, and when needed, load the ISO file under DOS through grub to install the system. No need for any discs or optical drives at all.

Floppy disks and hard disks can be emulated with IMG because they both use a unified BIOS standard. By simply changing the pointer to INT13, the read and write operations can be redirected to another place, such as an IMG file. This is emulation.

The situation with optical discs is quite different. Currently, optical discs cannot be operated through the BIOS's int interface. We cannot achieve emulation by modifying the int vector.

grub for dos 0.3.x is an attempt. First, it aims to "hard diskize" the optical disc so that the optical disc can also have the BIOS's int interface. When this interface gains more software support and forms a standard and scale, we can use ISO to emulate CDROM.

It is still very far away, so don't have too high expectations.