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DOS Programs

DOS PROGRAMS

Knowing a few things about DOS may help further your understanding of how DOS works, making you a more skilled DOS user. This section includes information about:
  • System control programs 
  • Internal and external commands
  • DOS program summary
  • Device designation (or names)
 
System Control Programs:  There are four essential programs associated with the control of your computer and the way it interacts with 1) programs; 2)your keyboard and display screen; and
3) attached devices like disk drives, printers, and modems. These are:

  • Boot Record
  • BIO.COM
  • DOS.COM
  • COMMAND.COM

Only the COMMAND.COM program is displayed when you view a directory of filenames located on a disk. You can see the BIO.COM and DOS.COM programs by typing CHKDSK /V and pressing Enter (sometimes engraved Return) which checks the files and storage space on your disk. The /V option lets you view filenames. The purpose of the system control program is briefly described for you in the following paragraph:

The Boot Record: The term boot or bootstrap, when used with computers, means start or start-up. When you boot your computer, you are turning it on and loading the operating system into your computer's memory. This includes reading the boot record into memory, which passes control to DOS. Next, DOS checks for the presence of  BIO.COM and DOS.COM. If these files are found, the DOS prompt is displayed on your screen. This prompt, normally and A>, B>, or C>, depending on which disk drive is active, invites you to type a command. If BIO.COM and DOS.COM are not found, an error message is displayed.

Your computer does not display not boot without a boot record. Instead, an error message is displayed telling you to insert a system disk. The boot record is located on track 0, sector 1, side 0 of your formatted DOS disk. If you have a hard disk, the boot record is located on the first sector of the first cylinder of the DOS partition.

The BIO.COM Program: This program, called IBMBIO.COM on IBM's DOS version, interacts between your computer's ROM BIOS (read-only memory basic input/output system) and calls from the DOS.COM program described next. At start-up, BIO.COM resets the disk system and initializes attached devices. BIO.COM always contains at least five device drivers, which are used to control the operation of your keyboard, screen, printer, disk controller, and system clock. Other device drivers that often are included control large, external hard disks, serial communications. joy sticks, and mouse devices.

The final task performed by BIO.COM is to load the command processor program, COMMAND.COM. The BIO.COM file is programmed by the manufacturer of your computer system. Therefore, the specific type and number of device drivers vary between computers.

The DOS.COM Programs: This program, called IBMDOS.COM on IBM's DOS version, interacts directly with applications programs and the BIO.COM program described above. You can think of this program as the bridge between applications programs and BIO.COM, as it intercepts program calls for printing, data storage or retrieval, information display, and so on, and routes these calls to the BIO.COM program, which responds to the request with the appropiate reaction.

The COMMAND.COM: The COMMAND.COM program is called the command processor. It intercepts, or reads, commands from the keyboard and executable command files. These files have the filename AUTOEXEC.BAT or the file extensions.COM and .EXE. COMMAND.COM also produces the DOS disk prompt (A>), performs error checking, and displays error message when system errors are detected.
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