DOS

Federal Board | Past Papers | Notes | A-Level

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(a) Why is DOS called Disk Operating System ? Also write its major tasks.
(b) Why is DOS divided into two types of commands (internal and external) ? Explain it.

(a) DOS uses a command line, or text-based interface, that allows the user to type commands. DOS is called Disk Operating System because it is stored on the disk of a computer. The major tasks the DOS must carry out are:

  • To control input and output devices
  • To enable user to load and execute program
  • To maintain an orderly system of data on the disk

(b) DOS internal and external commands

DOS Internal Commands
DOS internal commands are loaded automatically into the memory (RAM) during boot up process when you start your system. These includes ( CLS, DIR, DEL, DATE, TIME, EXIT etc.) that are needed on regular basis.

DOS External Commands
Usually external DOS commands are required less frequently. These reside on disk and are loaded into RAM only when needed. Some of the external DOS commands are , CHKDSK, DELTREE, FORMAT, XCOPY etc.