Monday, 8 October 2018

Introduction of MS-DOS ?

MS-DOS - A Introduction :- 

                                                                        MS-DOS or Microsoft Disk Oprating System, was initially developed by Tim Patterson and later sold to Microsoft Corporation US. Microsoft and IBM jointly introduced MS-DOS in 1981. In 1980s the mostb popular OS for personal Computer was MS-DOS. However, with the advent of MS Windows OS, its popularity started reducing.

This Disk Oprating System performs a number of essential jobs that include:

♦ Control of the various  application programs such as word processor and electronic spreadsheets. it create an environment that allows these programs to talk to computers.  

♦ House keeping and file management utilities.

♦ Automation of the repetitive tasks through automatic execution.

♦ Controlling the way the computer interprets certain command.

♦ Controlling the way, certain information is displayed on the screen.

Different versions of MS-DOS have been made available by Microsoft Corporation from time to time.

Structure of MS-DOS:-  
                                                               The structure of MS-DOS operating system is in figure 2.1. it contains the following two parts:
1.  DOS Kernel

2.  Command processor/interpreter (Shell)

DOS Kernel:- 
                                    DOS Kernel is a program that communicates with device drivers through I/O provides a collection of hardware independent service called system function. Program can access system function by loading parameters and then transferring control to the operating system by means of software interrupts. Kernel also performs  various managerial functions like file management, memory management and divice management, etc. It is supported by MSDOS.SYS  (IBMDOS.COM on IBM PC).

Command Interpreter/Processor (Shell):- 
                                                                                                          Command interpreter provides user interface between an operating system on a computer and the user. It is supported by COMMAND.COM file (in both MS-DOS and PC-DOS). A command interpreter the user. It is responsible for parsing and executing user's commands including the loading and exectuing of other programs from a disk or other mass storage devices. COMMAND.COM file has two portions.

♦  Resident Part:-  This part is availble at all times once it has been loaded in RAM at the time of booting. It is kept in protected mode. It contains internal commands.

♦  Transient Part:-   This part of COMMAND.COM resides on the disk. It contains external command in the form of files, which get loaded into memory when a particular command is used.

Booting:- Booting is a process that starts up a computer. When the system is switched ON, first the BIOS present in the ROM checks for proper functioning off all the peripheral devices attached to the system. This process is called POST (Power On Self Test). It also checks for the primary memory of the system. It then searches for the operating system and, when located, loads it into the main memory. The main files of MS-DOS are: COMMAND.COM, IO.SYS, MS-DOS.SYS, AUTOEXEC.SYS, CONFIG.SYS, HIMEM.SYS, etc.Booting is done in the following two ways:

       ♦ Cold Boot is done by turning ON the computer. In case of cold the memory and                            peripheral devices are checked before loading the operating system.
      ♦ Warm Boot is performed by pressing Ctrl, Alt and Del keys simultaneously. memory and           peripheral devices are not checked in case of warm boot and operating system is directly             loaded.  

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