When the SYS command is used, the

is usually used. We usually use the C drive. After the boot, the prompt is displayed as C:, but sometimes we also need to start from the A drive. For example, if the computer is infected with a virus, it must be non-toxic. After the floppy disk is booted, use antivirus software to kill the virus. With the correct settings, insert the floppy disk with the boot function into the A drive. After the computer starts, the prompt is A:. So, how can we make a floppy disk have a boot function?

DOS provides a command specifically for making a boot disk. This is the sys command. The format of the sys command is very simple: sys drive name, for example, at the C drive prompt, type: sys a:, the system file on the C drive is transferred to the A drive, and the disk in the A drive is made into the boot disk. If the A disk is booted, sys c: is to transfer the system file on the A disk to the C disk.

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

When we use the dir command to view the boot disk we just created, we can see that there are COMMAND.COM files in the root directory, but we can't see the two files IO.SYS and MSDOS.SYS. In fact, these two files are system files. You can't see them directly with the dir command. If we use the dir/as command, we can see them. The purpose of this command is to view the system files. In addition, we can't simply use the copy command to make a boot disk, because the system files copied with the copy command are not necessarily placed on the front track.