Friday, October 12, 2007

External Commands

Continued in Everything about DOS...



In the previous post, we saw that INTERNAL COMMANDS are those commands that are in present in the file COMMAND.COM. These are loaded into the memory every time the computer boots up.

Obviously not all of the commands can be loaded into the system memory at boot-up because they may not be needed, may be they are used infrequently or maybe they are too heavy in size. These commands are, hence, not included in command.com but are placed separately as individual files in the Windows System Directory (x:\windows\system32\ for Windows XP but may depend on the installation if customized. X:\ is the drive letter in which the Windows is installed.)

These commands can then be called from command-line as and when needed. These commands are known as EXTERNAL COMMANDS

LIST OF EXTERNAL COMMANDS:

append

assign

attrib

backup

chkdsk

command

comp

dblspace

debug

defrag

deloldos

deltree

diskcomp

diskcopy

doskey

dosshell

edit

emm386

exe2bin

expand

fasthelp

fastopen

fc

fdisk

find

format

graftabl

graphics

help

himem

interlnk

intersvr

join

keyb

label

mem

memmaker

mirror

mode

more

msav

msbackup

mscdex

msd

nlsfunc

power

print

replace

restore

scandisk

select

setver

share

sort

subst

sys

tree

undelete

unformat

vsafe

xcopy

Please note that you might not find all of these files on every computer. This will depend on things like which version of DOS you have installed. In some cases Microsoft replaced one file with a different file in later versions. An example of this is CHKDSK (i.e. "Check Disk"). This name survives in Windows NT, but in DOS (and later, Windows) this program/applet was replaced by the later SCANDISK. So look at this as a list of some of the files you might find on your computer. You may have some that are not on this list, as well. Also, note that other programs will sometimes install files in the DOS directory. In particular, Windows 3.x installed many of its files in this directory, and sometimes updated the versions that DOS originally installed.

One file that is very important, though it is not a DOS command, is the included copy of BASIC. In earlier versions of DOS this was called GWBASIC, and in later versions, QBASIC. One of the important external commands, EDIT, is actually a BASIC program, and will not run unless BASIC is present.

Extensions, Help, and associated files

External commands are files, and as such have file extensions. Generally these will be either *.EXE or *.COM. An *.EXE file is what is called an executable file. This is a file that is compiled to run as a program. To this day, any Windows program is run from an *.EXE file. The other type. *.COM, is the original "Dot Com". This refers to a command file. A few of these files will be *.SYS, which are system files, such as the IO.SYS and MSDOS.SYS files we discussed in Lesson 2. Another file type is the *.OVL file, which means overlay. This file type is found with backup programs, particularly.

Often these external files will come with Help files as well. Help files have the extension *.HLP which can be viewed with Windows Help Viewer in-built program.


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