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Introduction to DOS 

Added: 01/02/2001, Hits: 4,733, Rating: 0, Comments: 0, Votes: 0
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Disk Operating System(DOS) is a single user single-process operating system that uses a command line interface known as a DOS prompt. Files with .COM, .BAT and .EXE can be executed from the prompt. The following is a list of DOS system files in the order that they are called during the boostrap process:

  • IO.SYS - Located in the Root and defines basic Input/Output routines for the processor. Is Hidden and Read Only. This IS required for OS start-up. IO.SYS runs MSDOS.SYS, CONFIG.SYS and then COMMAND.COM.

  • MSDOS.SYS - Located in the Root and defines system file locations. Is Hidden and Read Only. This IS required for OS start-up.

  • CONFIG.SYS - Located in the Root and automatically loaded by MSDOS.SYS. This loads low level device drivers for hardware and memory drivers such as HIMEM.SYS and EMM386.EXE. Other drivers include ANSI.SYS, DISPLAY.SYS, KEYBOARD.SYS, PRINTER.SYS and DRIVER.SYS which assigns drive letters to floppy drives. CONFIG.SYS is not required for OS Start-up.

  • HIMEM.SYS - Controls Extended Memory management in the extended memory area. Located in C:DOS and is not required for OS start-up.

  • EMM386.EXE - Controls Expanded memory in the upper memory area. Located in C:DOS and is not required for OS start-up.

  • COMMAND.COM - This is the command specifier. It is responsible for the command prompt and contains all the internal commands such as DIR, COPY, and CLS. Located normally in the Root directory but can be located elsewhere and specified in the Autoexec.bat with a "SET COMSPEC=". This carries no attributes and is required for OS start-up.

  • AUTOEXEC.BAT - Located in the Root and automatically executed at start-up. Runs Programs (Prompt, WIN, CLS etc) and set commands (Path, Comspec etc..). Also calls other batch files. This is not required for OS Start-up.

The DOS interface is a command line prompt at which commands are entered and can utilize wildcards such as the asterisk(*). Many of the DOS commands are internal which means that they are stored in COMMAND.COM. The external commands are supplemental utilities. The following list explains the most common commands and utilities.
  • MEM - Shows the amount of memory in the system, how much is being used, how much is free and other useful memory information.

  • DIR - Shows the contents of the current directory.

  • CD - Change directories. For example, "cd windowssystem32".

  • COPY - Copies a file from one location to another. Example: COPY C:windowsdesktopfile.txt A:. This would copy file.txt from the desktop to the floppy drive.

  • XCOPY - This command is used like the COPY command, however, it copies all files and subdirectories to the new location.

  • ATTRIB - Used to display and change file and folder attributes. Example: ATTRIB +H file.txt. This would change file.txt to be a hidden file. The various attribute options are hidden, read only, system and archive. You would set a file to hidden either for security reasons or to prevent users from deleting it. Read only is used when you wish to prevent users from modifying the file. System is reserved for system files.

  • VER - Displays the version of the operating system being run.

  • SETVER - If the SETVER command is loaded in CONFIG.SYS, the SETVER command displays the version table and reports a DOS version number to programs or device drivers for backward compatibility.

  • VER - Will display the version of the operating system that is running.

  • FORMAT - Used to mark tracks and sectors on a hard drive and create a file system. When using the format command, everything on the drive is erased. Can also be used with floppies. If used with the /s switch the boot files will be copied to the disk.

  • FDISK - A utility used to partition hard drives and repair the MBR.

  • MKDIR - Make Directory. Used to create a new directory as in the following example: MKDIR files. This would create a new directory called files.

  • SYS - Transfers system files to another disk.

  • MSCDEX - Provides access to the CDROM. Typically, this is loaded by the AUTOEXEC.BAT.

  • EDIT - Runs the MS-DOS Editor which is an ASCII text editor that can be used to edit CONFIG.SYS and AUTOEXEC.BAT files.

  • DEL(ERASE) - Deletes specified files from the hard drive.

  • SCANREG - Runs the Windows Registry Checker which checks the registry for errors and allows you to backup and restore the registry.

DOS file names must be unique in the directory that they are located, can be 8 characters or less and contain a 3 character extension. DOS names cannot contain punctuation marks. The asterisk(*) and question mark(?) can be used as wildcards in DOS.

DOS includes a couple of keyboard shortcuts that can be used. F1 will type in the previous command entered 1 character at a time. F3 will enter the previous command with one keystroke.

Memory Management
  • First 640k is Conventional Memory

  • 640k to 1024k is Upper Memory

  • Above 1024k is Extended Memory

  • HIMEM.SYS is loaded in CONFIG.SYS as the first driver to manage the Extended Memory are and to convert this to XMS (Extended Memory Specification). The first 64k of extended memory has been labelled High Memory (HMA). DOS can be put here by putting DOS=HIGH in CONFIG.SYS.

  • EMM386.EXE is loaded in CONFIG.SYS after HIMEM.SYS has been successfully loaded. This is used in the hardware reserved 384k of space in upper memory (640k-1024k) and creates EMS(Extended Memory Specification).

  • Virtual Memory relies upon EMS (therefore EMM386.EXE) and uses hard disk space as memory.

SMARTDRV.SYS is a disk caching program for DOS and Windows 3.x systems. The smartdrive program keeps a copy of recently accessed hard disk data in memory. When a program or MSDOS reads data, smartdrive first checks to see if it already has a copy and if so supplies it instead of reading from the hard disk.

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