Every field develops its own jargon. This can facilitate communication among specialists and make the language more colorful, but it can also be very difficult for outsiders or newcomers to understand.
The English language terminology used in the computer field can be particularly confusing for people who are relatively new to computers because (1) some words can have multiple meanings, (2) in some cases multiple terms exist for the same meaning, (3) usage for some terms is inconsistent, (4) some archaic terminology has survived whose meanings might not be as obvious as they once were and (5) some terms have been deliberately coined by dominant companies to be misleading as a means of helping maintain or boost their market shares and profits.
This confusion can add to the difficulty of studying what is already a complex subject. In order to help solve this problem, explanations of some of the most confusing terms are presented below:
binary The term (1) binary commonly refers to any system that uses two alternative states, components, conditions or conclusions. However, (2) a binary file is computer terminology for any file that does not consist entirely of plain text (i.e., human-readable characters). That is, it contains some sequences of bits (i.e., sequences of zeros and ones) that do not represent any characters. The term (3) binaries refers to files that constitute a ready-to-run program. In a technical sense, any computer file is really a binary file in that it can be reduced to a binary sequence (i.e., a sequence of zeros and ones).
command A command is an instruction telling a computer to do something. The term can refer to either (1) the name of a program to launch or to (2) a more complex instruction that might contain multiple program names as well as options (i.e., switches or flags that modify it in some pre-set way), arguments (i.e., input data, such as the names of files or directories) for each and redirection operators (e.g., pipes, which send the output from one command to be used as the input for another).
command line The command line literally means the line on the display screen into which a user types commands. However, it is usually used more broadly to refer to (1) a command line interface (CLI), which is an all-text display mode, and (2) as a synonym for a shell, which is a program that provides a command line interface and the command lines on it and which executes the commands typed into it and displays the results.
computer The term computer can refer to just a (1) a boxy device which contains a hard disk drive (HDD), memory, a CPU (central processing unit) and other circuitry, or it can refer to (2) the boxy device plus peripheral devices, such as a display, keyboard and mouse. The term can also refer to (3) a computer-on-a-chip, which is a tiny piece of silicon that contains the logic and some or all of the memory functions of a conventional computer. An embedded processor is really a miniature computer that is built into some product that does not resemble the conventional conception of a computer.
It should not be forgotten (although it often is) that the original meaning of the term computer was a person whose profession was to spend all day performing arithmetic calculations (i.e., computation) with a pencil and paper long before the days of electronic computers or even simple adding machines. However, modern electronic computers are fundamentally similar in that all of the seeming magic that they perform really consists likewise of just performing simple arithmetic calculations, although at an extremely high speed.
console The word console usually refers either to a large, full-featured version of an electronic product (e.g., a stereo system) that stands on the floor or to a control panel for an electronic product. However, in a computer context today it generally refers to the display mode that contains only text and no images and which occupies the entire screen of the display device (usually a CRT or LCD). That is, it is a type of CLI. Sometimes the term display console is used as a synonym for this meaning of console.
CPU A central processing unit, whose acronym is CPU, is the main logic unit of a computer. A CPU is a type of processor (i.e., a type of high density semiconductor chip), which is a synonym for microprocessor. A computer can contain a number of processors, including specialized chips for controlling various devices such as the HDD and display. A computer can also contain multiple CPUs, so the word central in CPU really indicates that it is the, or one of the, main logic units on a computer and not just a specialized processor for controlling some specific device or function.
crash A crash is the situation in which a computer program stops performing as expected and also stops responding to other parts of the system. To crash means the same thing as to hang, to lock up and to bomb. Crashes are usually caused by software problems and almost never damage hardware. This is very different from a head crash is the situation in which the magnetic head in a HDD makes physical contact with a disk (i.e., a platter) in a HDD while the disk is spinning, which can damage the disk and cause data loss.
cylinder The term cylinder can be confusing to people who are new to the intricacies of HDDs because a cylinder is usually thought of as a solid object with a circular cross section, such as a piston in an internal combustion engine. However, when used in a computer context, the term actually refers to only the outer surface of a cylinder shape, similar to a very thin tube or a can with its ends cut off. It refers to any set of all of tracks (concentric rings of data) of equal diameter in a HDD and can be visualized as a single, imaginary, circle that cuts through all of the platters in the drive. Platters are thin, high-precision disks that are coated on both sides with a high-sensitivity magnetic material and all of which are mounted on a single shaft in a HDD.
directory Also referred to as a folder on some operating systems, a directory is regarded on Unix-like operating systems as merely a special type of file that contains a list of names and other information about the files that appear to the user to be in it. Every directory on such systems is also a subdirectory (of its parent directory, which is the directory in which it is contained), with the exception of the root directory, which has no parent directory because it is the directory that contains all other directories and their subdirectories.
file On Unix-like operating systems everything is considered to be either a file or a process. This includes directories, which are regarded as just a special type of file. In this sense, it would be redundant to say files and directories. However, such an expression is commonly used because it might be clearer for new users who are not yet aware that directories are files and because it makes a distinction between all files and files that are not also directories.
filesystem The term filesystem can mean (1) a way of organizing files and (2) the hierarchical arrangement of directories. Each of these meanings can apply to a network, a computer, a disk, or a partition (i.e., a logically independent section of a disk). A filesystem in the second sense can contain multiple filesystems in the first sense. Thus, for example, a HDD, computer or network can contain multiple types of filesystems. However, a partition can contain only a single type of filesystem.
Flash memory, sometimes called flash RAM, is a type of semiconductor device that combines important features of both memory and storage, including high-speed access and retention of data in the absence of a power supply. Flash memory should not be confused with (2) Flash animation graphics, a somewhat controversial animation technology that has become widespread on websites in recent years, mostly for advertisements. (3) To flash a BIOS refers to rewriting the contents of a BIOS (basic input output system), which is typically housed in a flash memory chip on the motherboard (i.e., the main circuit board of a computer).
free software The term free software is most commonly used to refer to software that is free both in a monetary sense (i.e., no requirement for payment) and with regard to use (i.e., no restrictions on copying, modifying, redistributing, etc.). However, this concept is often confusing to novices, who think of it as meaning just the former and do not give much, if any, consideration to the latter. Such users might consider programs that are given away at no cost to users but which have restrictions regarding their usage to be free, but such programs are not free in the sense of free software as the term is commonly used in the computer industry today.
Free software is generally the same as open source software because both make the source code (i.e., the version in which it is originally typed by a human in a programming language) freely available; however, there are some subtle differences in philosophy between the advocates of free software and those of open source software. Freeware is very different from free software: it consists of programs (such as Adobe's Acrobat Reader and Microsoft's Internet Explorer) that are available to users at no monetary cost but for which there are generally severe restrictions regarding their use (e.g., modification is prohibited).
hard disk A hard disk is commonly used as a synonym for hard disk drive, but it is technically just one of the multiple platters that are contained in a HDD. However, a floppy disk is not a synonym for a floppy disk drive, as the disks can be removed from the drive.
head The word head has several meanings in a computer context. One is (1) a magnetic head, which is a high precision electromagnet that is used to read and write data on magnetic media (i.e., HDDs, floppy disks and magnetic tape). But the term is also commonly used for analogous devices for optical media, such as CDROM drives. A second type of meaning is (2) the head command on Unix-like operating system, which reads the first lines of a text file. A third meaning is (3) the HTML (hypertext markup language) <head> tag, which is used near the top of web pages to hold metadata about the page.
home There are at least four common meanings for home or terms that include it. The most common use is to refer to (1) a user's user's home directory, which is the directory in which a user generally keeps its own files and programs. The (2) /home directory (i.e., preceded by a forward slash) is the directory that contains the home directories of ordinary users. (3) HOME (all upper case letters) is the environmental variable that tells the location of the home directory for the current user. Environmental variables are a class of variables that tell the shell how to behave as one works at the command line or in scripts (i.e., short programs). (4) A home page is the entry page on a web site, and a page which usually provides the name of the site, tells briefly what it is about and contains links to other key pages on the site.
image The term image is usually used to refer to (1) a picture, such as a jpeg or gif file. However, it can also mean (2) an exact (i.e., bit-for-bit) copy of a file, particularly an executable (i.e., ready-to-run) program, especially in the context of making a copy of such a program on another disk.
Internet The (1) Internet (spelled with an upper case I) is the world-wide network of interconnected computer networks (e.g., commercial, academic and government) that operates using a standardized set of communications protocols called TCP/IP (transmission control protocol/Internet protocol) or the Internet protocol suite. An (2) internet (spelled with a lower case i) is a network that is composed of a number of smaller computer networks. The Internet is an internet that is vastly larger than any other internet and can be considered to be the ultimate internet; it connects thousands of networks and hundreds of millions of computers throughout the world. An intranet is a private network that uses Internet protocols.
The term kilobyte is commonly used to refer to one thousand bytes. However, the more technical meaning is 1024 bytes. Both usages are correct, and, fortunately, the difference is sufficiently small that it can usually be ignored. There are similar discrepancies for other multiples of bytes, including megabyte (million bytes) and gigabyte (billion bytes).
Linux The word Linux is most commonly used to refer to the operating system that was originally created in 1991 by Linus Torvalds while he was a student in Finland. However, technically, it refers only to the kernel (i.e., the core of the operating system) and not the hundreds of utilities and other programs that are almost always used together with it. Also, there is a continuing controversy about whether the name of the operating system should be called Linux or GNU/Linux, because many of its utilities and other programs were developed by the GNU (GNU is not UNIX) project.
logical partition This can be confusing because a partition is defined as a logical division of a HDD, but a logical partition is any partition that is carved out of an extended partition. An extended partition is a primary partition that is designated to be available for carving up into additional partitions in order to increase the number of partitions to more than the maximum of four primary partitions.
memory The term memory most commonly refers to main memory, which does not include cache memory and virtual memory. Cache memory is a small amount of high-speed memory that is used to hold data which is currently being used or is frequently used. Both main memory and cache memory physically consist of random access memory (RAM) chips, but the former uses relatively low cost DRAM (dynamic RAM) chips and latter uses the faster and more expensive SRAM (static RAM) chips. Virtual memory is simulated main memory which is attained by temporarily storing a portion of RAM contents on the swap partition of the HDD. A small number of ultra-high speed memory cells, called registers, are also built into CPUs.
mount point A mount point, also written as a single word (i.e., mountpoint), is the directory in which a partition or other storage device (e.g., a floppy disk or CDROM) is logically attached to the main filesystem. Users often first encounter this term during the partitioning phase of installing Linux. And it can be confusing because the term implies a point but it is actually a directory, which is usually thought of as being a container (i.e., for files and other directories) rather than a point. However, it should be kept in mind that a directory can, in fact, be thought of as being more analogous to a point than to a container because directories are merely a special type of file in Unix-like operating systems.
naked PC This is an example of a term that was deliberately coined to be misleading. It refers to a personal computer that is sold without any operating system installed on its HDD. It is designed to imply that there is something wrong with selling a computer without an operating system already installed, which there certainly is not (at least if one believes in free choice for consumers). Common sense would imply that the term naked PC should refer to a computer without a case covering its internal components, just as the term naked light bulb refers to a light bulb in a lamp without being covered by a lampshade.
option An option, which is also called a flag and a switch, is a single letter or a full word that modifies the behavior of a command in some predetermined way. Flag and switch are now less commonly used than option, but they tend to sound more professional. The complete list of options for any command can usually be found by using that command's --help option or by referring to its man (i.e., online manual) page.
path A (1) path (all lower case characters) is the sequence of directories in which the operating system searches for executable files (i.e., ready-to-run programs) corresponding to commands issued by users. (2) PATH (all upper case characters) is the environmental variable that contains the path for any particular user. This variable can be different for different users, and the path for the root user typically differs from those for ordinary users. The (3) classpath is the sequence of directories that the system searches to find .class files in a Java runtime environment.
plain text Plain text refers to any string (i.e., finite sequence of characters) that consists entirely of printable characters (i.e., human readable characters) and, optionally, a very few specific types of control characters (e.g., characters indicating a tab or the start of a new line). Plaintext (single word) is a term used in cryptography that refers to a message before encryption or after decryption. That is, it is a message in a form that is easily readable by humans. Plaintext is written in plain text.
platform The term platform as used in a computer context can refer to (1) the type of processor and/or other hardware on which a given operating system or application program runs, (2) the type of operating system on a computer or (3) the combination of the type of hardware and the type of operating system running on it. The first meaning, also called the hardware platform, can refer to the the type of system in general (such as mainframe, workstation, desktop, handheld or embedded) and/or the specific type of processor (such as x86, SPARC, PowerPC or Alpha). For example, the statement, "Linux can run on many platforms," can refer to the fact that Linux runs on everything from mainframes to embedded systems and/or to the fact that it runs on a variety of processors.
port This term has three very different meanings. One is (1) a combined physical and electronic connector, typically located on the back of a computer, into which a mating connector on a cable can be inserted. Such ports are usually classified as being either parallel (multiple bits sent simultaneously) or serial (bits sent one by one). A second meaning is (2) a logical connection used in networking. Each such port is assigned a port number, and some of them are standardized, such as 80 for HTTP (hypertext transfer protocol) traffic. A third meaning is (3) to modify a program so that it will run on another operating system or processor type. For example, many Linux programs have been ported to Microsoft Windows.
print The word print is traditional UNIX terminology that can refer to displaying text output on the monitor as well as writing it to a file or sending it to a printer. It is a holdover from the days before monitors were common and when most output was, in fact, printed by a printer on paper (or punched into tape or cards). Although this term is sometimes said to be archaic, it is still widely used, particularly in the man online manual.
root The word root has several common meanings with regard to Unix-like operating systems. The most frequent is (1) root user, which is the administrative user or superuser. It is usually just referred to as root (not preceded by an article), and sometimes it is referred to as the root account. The (2) root directory is the single directory that contains all other directories as well as their subdirectories and files and which is designated by a single forward slash ( / ). It derives its name from the fact that it is analogous to the root of a tree. The (3) /root directory, not to be confused with the root directory, is the home directory of the root user. The (4) root filesystem is the filesystem that is contained on the HDD partition on which the root directory is located, and sometimes it is the only part of the filesystem that can be utilized when attempting to repair a damaged operating system. A (5) rootkit is a set of tools used by an intruder after breaking into a computer system.
running A process is an instance of a program that is running (i.e., operating or executing). Thus, it would seem logical that processes are running, too. However, any given process is actually running (i.e., progressing in the CPU) only a fraction of the time that the program it represents is running; the rest of the time it is waiting for its next turn to progress in the CPU. Thus the expression a running process refers specifically to a process that is currently active in the CPU of a multitasking operating system rather than processes which are currently awaiting their next time slices (i.e., alloted turns) in the CPU. A multitasking operating system is one in which multiple processes operate seemingly simultaneously by taking turns to progress in the CPU.
server The term server can refer to (1) a software program that provides a specific kind of service to client software running on the same computer or other computers on a network. It can also refer to (2) the computer on which that software runs or (3) the combination of the software and hardware. Some beginners confuse the term with the term mainframe, which is a very large and heavy duty computer; this is logical because years ago the two were essentially the same thing. Today, virtually any computer can be used as a server.
software piracy So-called software piracy is an example of a term that was created for its dramatic public relations value rather than because of any relationship to the traditional usage. It is a controversial term, just as the concept itself is highly controversial, because it implies that people or organizations who create or use copies of computer programs in violation of their licenses are similar to pirates. Pirates are violent gangs that raid ships at sea in order to steal their cargoes and rob their crews; they also frequently injure or kill the crews and sink their ships. Many people who have heard about real pirates can easily sense that this term is a great exaggeration when applied to software. The term unauthorized copying might be a much more appropriate alternative.
switch The word switch can refer to (1) a network switch, commonly called just a switch, which is a network device that is used to connect segments of a LAN (local area network) or multiple LANs and to filter and forward packets among them. It can also refer to (2) an option, which is a single-letter or a full word that modifies the behavior of a command in some predetermined way and which is also sometimes called a flag.
umount This is the command to logically disconnect a partition, floppy disk, etc. from the main filesystem. umount might appear to novices to be a misspelling of unmount, but it is not. And it may seem to be a nuisance to have to be concerned about mounting and unmounting in Unix-like operating systems, because such tasks are automated and hidden from users in the Microsoft Windows systems. Mounting and unmounting can likewise be automated in Unix-like operating systems, but the option of doing it manually provides for greater system flexibility and security.
Unix The terms UNIX (all upper case letters) and Unix are a source of never-ending confusion, controversy and even legal battles. The former is the name of the original UNIX operating systems that was written by Ken Thompson at Bell Labs in 1969 as well as of its direct descendants (e.g., System V). It is also a trademark that is now owned by The Open Group, an international industry consortium that attempts to protect its status as a trademark and prevent it from becoming a generic term (and thus no longer a legally valid trademark). However, many people in the computer field refer to all Unix-like operating systems as being UNIX or Unix.
A Unix-like operating system is a system that has functions and behavior similar to the original UNIXs developed at Bell Labs and subsequently at the University of California at Berkeley (UCB), even if they are clones such as Linux and MINIX. Apple Computer refers to its OS X operating system as being UNIX because it claims that this term has become generic and thus anyone can use it without restrictions; this has resulted in a lawsuit by The Open Group. The BSD operating systems (which were derived from the version of UNIX developed at UCB) and Linux generally avoid referring to themselves as UNIX or Unix in order to avoid potentially costly legal problems.
windows The term window has long been used by the computer industry to refer to a (usually) rectangular portion of the display on a computer monitor screen that presents its contents (e.g., the contents of a directory, a text file or an image) seemingly independently of the rest of the screen. Windows are one of the elements that comprise a graphical user interface (GUI). This term was later incorporated by Microsoft into the family name for its GUI-based operating systems, i.e., Microsoft Windows. Because the terms window and its plural form, windows, are generic words (which have been in use in the English language for hundreds of years), they cannot be trademarked or owned by any one company, in the opinion of many legal experts.
Specialized terms are defined and hyperlinked (if an appropriate page exists on this site) the first time they are used on this page. They are also defined and hyperlinked in the event that a entry about a specific term follows its first usage.
Created August 31, 2005. Last updated April 22, 2006.
Copyright © 2005 - 2006 The Linux Information Project. All Rights Reserved.