The modern DOS operating system is distributed on 3-5 high density floppy disks. It comes with backup utilities and (depending on how the lawyers feel) disk compression drivers. However, all the stuff that goes into C:\DOS and its subdirectories are programs and utilities. The core DOS operating system consists of six files:
The boot sector is a 512 byte record placed at the beginning of the C: drive when DOS was installed, or placed there subsequently using the "sys c:" command.
Two "hidden" files are stored in the root directory of the C: drive. They do not show up in a DIR listing unless the /A switch is used. On IBM PC DOS systems, they are IBMBIO.SYS and IBMDOS .SYS. On MS DOS systems, they are called IO.SYS and MSDOS.SYS. These files form the kernel of the DOS system.
COMMAND.COM is the "shell" or command interpreter. It prints out the "C:\> " prompt and reads user commands. It also supports BAT files.
The user configuration files are CONFIG.SYS and AUTOEXEC.BAT. The reader is assumed to be familiar with these files.
COMMAND.COM is initially stored in the C:\ root directory. The problem is that OS/2 and Windows NT have their own versions of COMMAND.COM. To avoid confusion, each COMMAND.COM should be stored in the subdirectory that belongs to its particular operating system. In normal use, this means that the DOS version should be in C:\DOS. To relocate it, two statements must be added to the user configuration files:
"SHELL=C:\DOS\COMMAND.COM" is added to CONFIG.SYS.
"SET COMSPEC=C:\DOS\COMMAND.COM" is added to AUTOEXEC.BAT.
The hidden files IBMBIO, IBMDOS, IO, or MSDOS have names that do not conflict with each other or with any system file belonging to any other operating system. They can stay in the C:\ root directory no matter what gets added to the system. This means that the volatile part of the DOS system consists of the boot record, C:\CONFIG.SYS, and C:\AUTOEXEC.BAT.
Putting DOS on a Floppy
To install a copy of the DOS system files on a floppy, simply issue the command:
FORMAT A: /S
Recovering Damaged DOS System Files
If the DOS system files have been clobbered, boot the same release of DOS from a floppy. When using the Install Diskettes for DOS, wait till the first panel appears and then escape from the installation system to the command prompt. Type
SYS C:
COMMAND.COM is initially stored in the C:\ root directory. The problem is that OS/2 and Windows NT have their own versions of COMMAND.COM. To avoid confusion, each COMMAND.COM should be stored in the subdirectory that belongs to its particular operating system. In normal use, this means that the DOS version should be in C:\DOS. To relocate it, two statements must be added to the user configuration files:
"SHELL=C:\DOS\COMMAND.COM" is added to CONFIG.SYS.
"SET COMSPEC=C:\DOS\COMMAND.COM" is added to AUTOEXEC.BAT.
The hidden files IBMBIO, IBMDOS, IO, or MSDOS have names that do not conflict with each other or with any system file belonging to any other operating system. They can stay in the C:\ root directory no matter what gets added to the system. This means that the volatile part of the DOS system consists of the boot record, C:\CONFIG.SYS, and C:\AUTOEXEC.BAT.
Putting DOS on a Floppy
To install a copy of the DOS system files on a floppy, simply issue the command:
FORMAT A: /S
Recovering Damaged DOS System Files
If the DOS system files have been clobbered, boot the same release of DOS from a floppy. When using the Install Diskettes for DOS, wait till the first panel appears and then escape from the installation system to the command prompt. Type
SYS C:
Reference : http://pclt.cis.yale.edu/pclt/BOOT/DOS.HTM
