Glossary - C

4 A B D E F G H I K L M N O P R S T U V W X 

CDFS or CD-ROM File System:  The file system which supports CD-ROM drives. 
 This is typically implemented as a distinct file system in 32-bit 
operating systems like OS/2 and Windows NT.  On other platforms it is 
implemented as a component of or addition to the underlying general file 
system for disk drives. 

Character Device:  A physical device for input or output which must 
communicate with your computer one character at a time.  Examples include 
the console, communications ports, and printers.  See also Block Device. 

Character Mode:  A display mode in which output is displayed in a fixed 
font, typically with 80 columns in a line and 25 lines on the screen (some 
systems allow you to increase the number of rows and columns to other 
fixed sizes), and which cannot display graphics or pictures.  See also 
Graphics Mode. 

CMD File:  See Batch File. 

CMDLINE:  An environment variable used to extend the command line passed 
to another program beyond its normal length limits. 

Cold Reboot:  The process of restarting the computer in a way that 
physically resets most hardware devices, typically by pressing a reset 
button, or by turning the power off and back on.  See also Warm Reboot. 

Command Completion:  A CMD.EXE feature which allows you to recall a 
previous command by typing the first few letters of the command, then an 
up-arrow or down-arrow. 

Command Echoing:  A feature which displays commands as they are executed. 
 Echoing can be turned on and off. 

Command Grouping:  A CMD.EXE feature which allows you to group several 
commands with parentheses, and have them treated as a single command for 
most purposes. 

Command History Window:  A pop-up window used by CMD.EXE to display the 
command history, allowing you to choose a previous command to modify 
and/or execute. 

Command History:  A CMD.EXE feature which retains commands you have 
executed, so that they can be modified and re-executed later. 

Command Processor:  A program which interprets commands and executes other 
programs.  Sometimes also called a Command Interpreter. 

Command Recall:  See Command History. 

Command Separator:  A character used to separate multiple commands on the 
same command line. 

Command Tail:  The portion of a command consisting of all the arguments, 
i.e., everything but the command name itself. 

Compound Command:  See Multiple Commands. 

Compression:  An operating system feature which compresses data as it is 
stored in a disk file, and decompresses it as it is read back, resulting 
in more efficient use of disk space (at a slight cost in processor time to 
perform the compression and decompression).  More generally, an approach 
to data storage which reduces repeated or redundant information to a 
smaller number of bytes in the compressed version than in the original, in 
order to minimize the space required to store the information. 

COMSPEC:  An environment variable which defines where to find the 
character-mode command processor to start a secondary shell. 

Conditional Commands:  A CMD.EXE feature allowing commands to be executed 
or skipped depending on the results of a previous command.   See also Exit 
Code. 

Console:  The PC keyboard and display. 

Console Mode:  See Character Mode. 

Control Character:  A character which is part of the ASCII code, but does 
not have a normal text representation, and which can usually be generated 
by pressing the Ctrl key along with another key. 

Coprocessor:  See Numeric Coprocessor. 

Country Settings:  The internal settings which tell the operating system 
how to interpret keyboard characters which vary from country to country, 
which character set to use, and how to retrieve and display date, time, 
and other information in the format appropriate to a particular country. 
 See also Code Page. 

CPU:  The Central Processing Unit which performs all logic and most 
calculations in a computer.  In PC-compatible systems, the CPU is on a 
single microprocessor chip. 

CR or Carriage Return:  The ASCII character "carriage return" (decimal 
value 13), generated by pressing the Enter key on the keyboard, and stored 
in most ASCII files at the end of each line. 

Critical Error:  An error, usually related to a physical or hardware 
problem with input, output, or network access, which prevents a program 
from continuing. 

Current Directory:  The directory in which all file operations will take 
place unless otherwise specified.  The current directory is typically 
displayed as part of the command prompt.  Also called the Current Working 
Directory. 

Current Drive:  The disk drive on which all file operations will take 
place unless otherwise specified.  The current drive is typically 
displayed as part of the command prompt. 

Cursor:  A movable marker on the screen to show where text will be entered 
when you type at the keyboard, or which object on the screen will be 
affected when a mouse button is clicked.  In character mode only the text 
cursor is available; graphical systems typically show both a mouse cursor 
and, when text can be entered, a separate text cursor.