Monday, 8 February 2021

MS-DOS

What is MS-DOS?

Microsoft Disk Operating System (MS-DOS) is a single-tasking operating system and a text-based user interface. MS-DOS uses 8086 real mode in CPU which was a 16-bit instruction set of the operating systems. MS-DOS could only address at most 1Mb of RAM.

MS-DOS Logo

DOS Interface Names

The DOS interface has many names such as

  • DOS Prompt
  • Command Prompt
  • DOS Shell
  • Command Shell
  • Command Interpreter
  • DOS Windows

Folders vs. Directories

In Windows, files are organized into FOLDERS and in DOS  these are called DIRECTORIES. The folders or directories are like drawers on a filing cabinet. Folders are easy to understand because you can see them, but directories are much more difficult to use because you can’t see them and because you have to learn the directory commands.

DOS Directory Commands

DIR - List files in current directory

CD - Change directory example: cd projects – changes to a directory called projects

MD - Make directory example: md backup – makes directory called backup

RD - Remove directory example: rd projects – removes the directory called projects

CD.. - Bring you back one level in the directory

CD\ - Brings you back to the root directory. i.e. C:\ for hard disk and F:\ for the floppy disk

C: - Changes focus to the drive called C:

F:\ - Changes focus to the drive called F:

TREE - A useful DOS command shows the entire directory structure.

DOS File System

It is one of the main functions of an operating system that allows us to store and work with data. A file is a “single name piece of data which can be store”.

DOS Filenames

Filename, “.” And file extension. No space allowed and the filenames are limited to 8 characters. For example, projects.xls, Here “project” is a filename and “xls” is a file extension.

DOS File Extensions

.com - Command file, run a small utility program

.exe - Executable program file, usually runs a major program example: (Excel) setup.exe

.bat - Batch file, example: autoexec.bat

.sys - Device driver file

.txt - Text file

.cab - Windows cabinet file

.zip - Winzip compressed file

.doc - Word document file

.xls - Excel file

.mdb - Access database

.ppt - PowerPoint presentation

.html - Web Page

Disk Storage

In this, each disk is divided into rings called Tracks. The track is broken into equally sized sections called Sectors. Each sector size is 512 bytes and a group of four sectors is called a cluster. In DOS, it is low-level file system technology because tracks and sectors cannot be seen when you view the properties of My Computer.

DOS File System

It keeps a record of the used sector detailing the physical location of each file on disk and also keeps a list of free sectors where new files can be stored. It was implemented using a File Allocation Table (FAT).

File Allocation Table (FAT)

It is also called FAT 16 or 16-bit file system. The 216 = 65,525storage locations (sectors) available and 65,525 x 512 = 32Mb. Maximum hard disk size using DOS as an operating system is 32Mb.

Example:

Filename

Location on Disk (Sector No.)

scsi.ppt

                                      451

reviews.xls

                                      10048

budget.doc

                                      698

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