DOS SYS command usage instructions

Ordinary application, we generally start with C, after the start, prompt display for C:, but sometimes we also need to start from a disk, for example, the computer infected with the virus, it is necessary to start with a non-toxic floppy, and then anti-virus software. In the correct setting, insert the floppy disk with startup capability into the a drive, and after the computer starts, the prompt is a:. So how do we get a floppy disk to start?

DOS provides a special command for making a startup disk, which is the SYS command. The SYS command has a simple format: SYS drive name, for example, at the C-disk prompt: SYS A: The system files on the C disk are transferred to a disk, and the disk in the a drive is made into a boot disk. If in the case of a disk startup, sys c: is to transfer the system files on disk A to the C disk.

In addition to the SYS command, you can also use the format a:/s command to make a system disk while formatting a disk. If a floppy disk has a boot function, it must have Io.sys, Msdos.sys, and Command.com three files in its root directory, and the first two files must be on the front track of the disk.

When we use the dir command to view the start-up disk we just made, we can see that there are command.com files under the root directory, but we don't see Io.sys, MSDOS. SYS these two files. In fact, these two files are system files, directly with the dir command is not visible, if we use the Dir/as command to see them, the role of this command is to view system files. In addition, we cannot simply use the Copy command to make the startup disk because the system files copied with the copy command are not necessarily placed on the front track.