DOS Commands for the Technician

DOS stands for Disk Operating System – a specialized set of program that you use to start and operate your computer. It is DOS that actually allows to run application program, create and manage files and coordinates all the components of your computer including optional devices such as mouse, printer, or modem. With very few exceptions any other program that you run on your computer does so with the help of DOS.

For a diskette to be able to load DOS, at least three files must be present on the disk. 1. Command.com 2. IO.sys 3. MSDOS.sys On the system, these files may have slightly different names. Collectively, they are called the DOS system files, or system files for short. Loosely, they form different parts of the DOS program. Only COMMAND.COM will show up when the directory is listed; the other two will be hidden. IO.SYS contains the program for sending and receiving information between computer and its peripheral devices like printers and disk. MSDOS.SYS contains the logic and routines for managing the data organization on the file system. COMMAND.COM is the DOS command processor. This is the interpreter between you and DOS. This program displays the command prompt, accepts command from the keyboard and interprets the command so they can be loaded upon your DOS. To be proficient in assembling and repairing computers, a technician must also be able to operate them. To attain competency, the following commands are the minimum that a technician must be able to use. Detailed instructions on their use and the options available within these commands can be obtained from any good DOS reference manual. Disk Files and Naming Conventions Any program or collection of data stored on a computer disk is saved in a file. The name is actually quite appropriate: Just as filing cabinet contains many different files typically stored in folders, a computer disk also stores many different files. Unlike filing cabinets, which typically contain only printed information, computer disks can store two different types of files: 1. Program Files – contains instructions that tell the computer what to do. In most cases, these files are created and maintained by you. 2. Data Files – contains information that a program not a person can read. Most data files cannot be displayed on the monitor because the information they contain is in a form that only the computer can understand. Data files are created and maintained by programs. A disk file is a collection of related information that is treated as a basic unit of storage. In order for DOS to identify a file on a disk, files must be assigned names. Two Types of DOS Commands A. Internal Commands – also called resident commands. It is a DOS command that resides in memory as part of DOS, which can be accessed anytime. 1. DIR: Used to find out what files are on a diskette or hard drive. 2. REN: Rename files. 3. CLS: Clear the screen; used mostly in batch files. 4. COPY: Make copies of files. This can also be used to change the name on the second copy of the file during the copy procedure. It can be dangerous, copying old data over new when files have same name. 5. VER: Tells what version of DOS you are using. 6. TYPE: Put contents of a file on the screen; terminates at the first Z in the file. This is useful for checking the contents of data files. 7. BATCH FILES: A powerful feature, consisting of lines each a DOS command, in a text file whose name ends with ". BAT". Typing the file name causes DOS to execute each line consecutively. 8. DEL: Erase (delete) files. 9. PATH: A "standing instruction" to the computer: If this program is not available in this directory, look for it in… 10. CTTY: A primitive way of controlling the computer via one of the serial ports; limited in its capabilities. 11. MD, RD, CD: Commands to make, remove, and change the default specified directories. 12. Root Directory Symbol ( \ ): When leading, used to indicate "starting from the root directory…" and as a separator when listing successive directories. 13. Using Wild Cards ( ? ), ( * ): When designating groups of files, ? is a single-character wild card, and * is a multiple-character wild card. 14. Dot ( . ) and double dot ( .. ): A single dot means the same as *.* when referring to the current directory. Double dots refer to the directory above the default. As a result, don’t try to delete these symbols or you will delete all of the files in either directory!

B. External Commands – also called transient commands. They are stored as small programs on disk. To use external command, DOS needs to be able to find it on disk. These files have an extension of .COM and .EXE. 1. RECOVER: A dangerous to be used only when problems are reported due to damaged file allocation tables. 2. FDISK: A dangerous program to be used to divide a hard disk; to be used only when all hard disk files are properly backed up. 3. FORMAT: A dangerous program that will remove all old data from a floppy disk or remove the directory of a hard disk. 4. DISKCOPY: A potentially dangerous program that will copy entire diskettes form one to another. Be sure you do not copy from a bad diskette to a good one, however, or you will have two copies of the bad diskette. 5. MODE: A particularly useful program used to set up the technical parameters for serial ports and to redirect the data heading for one port to a new one. 6. BACKUP: An important program to provide emergency copies of everything on a hard disk and to later add the files that have been updated since the last backup. One if the few programs that can split very large files between two or more diskettes. 7. RESTORE: The complement of backup, this program puts the files from backup diskettes back on to a hard drive. May copy an old file over a new one. 8. CHKDSK: An important program that will run some basic checks on a diskette or hard drive, reporting lost data area due to improper computer operation such as a shutdown of the computer without properly exiting some programs. 9. SYS: An important program that will place the two hidden files of the operating system onto a diskette or hard disk. Copying of the file COMMAND.COM will usually be necessary to make a proper bootable disk. Special Files COMMAND.COM: Part of the operating system, this file is required to interpret and execute all of the internal commands listed above. AUTOEXEC.BAT: A batch file with this special name will execute all of the DOS commands within it automatically on power-up of the computer. One of the important commands to include in this file is the location of your utility programs, a line beginning with the PATH command. CONFIG.SYS: A file containing information on how the computer should be customized for the operator’s software and hardware, if using a hard disk, this file should include command lines such as BUFFERS = 25 and FILES = 20. Dedicated Devices CON: The console, keyboard, and monitor as one unit. LPT1: or PRN: refers to the first parallel port, by default the printer port of a PC. LPT2 and PRN: are the designation for the second and third possible parallel ports. COM1 or AUX: refers to the first serial port. COM2: is the second possible serial I/O port. A:, B:, C:, etc. refer to the storage media drives. Most commonly, A: and B: refer to the first two diskette drives and C: is the first hard drive.