introduction
A user interface is the place where a computer and a person who wants to use it meet. A network interface is the meeting of a network and a computer that wants to talk to remote computers. An API (Application Program Interface) is the meeting of an application and a program that wants to use its functions.
An interface is a boundary where two things meet. An application can have several interfaces: one for customers to use, one to talk to the OS (Operating System), one for administrators to use for managing the application and one to let other programs use its functions.
what it is
Interfaces that administrators use come in three flavours: strawberry, chocolate and vanilla. The oldest type of interface that is still popular today is the CLI (Command Line Interface). The easiest type of interface to use, the one that dominates Apple and Microsoft land, is the GUI (Graphical User Interface). The type found all over the WWW is the web interface. This is a simple version of a GUI.
a CLI (Command Line Interface)
When the administrator logs into a UNIX system and the operating system has run a UNIX shell, the administrator is presented with a CLI (Command Line Interface).
$ |
A distinguishing feature of a CLI is its utter lack of prettiness. Everything is done with text. A CLI is possibly the least intuitive type of interface ever invented and is deeply unpopular with beginnners. The shell prompts you to type a command by displaying a couple of characters, such as "$" (a dollar sign), "person@host:" (something based on your login) or even "C:\>" (an imitation of an MS-DOS prompt). Using a CLI is faster, more efficient and more flexible than using a GUI (Graphical User Interface) and so is popular with experts.
A person types commands into a CLI and the shell types the answers. These commands are part of a programming language.
$ pwd /tmp $ |
remote
The most common way for an administrator to use a CLI is to run a terminal emulator on his computer and log into the remote computer.
a GUI (Graphical User Interface)
Every PC runs an OS (Operating System) that provides a GUI (Graphical User Interface). Most people prefer to use GUI features that a CLI does not have, like mice, color and different sized windows. Many of the applications in the LIC are controlled using GUIs.
An LIC is usually located far away from most of its users. Running a remote GUI is different
The windowing group of programs used by UNIX operating systems is called the X Window System, or X for short. I have no idea why it is called X. X windows differ from Microsoft windows because they were designed from the beginning to be run over a network. An X window on one computer can be displayed on any other computer that has a network connection to it and is running an X service.
The virtual desktop found on every OS everywhere is a big fat GUI. It provides an easy way to display several CLIs at the same time.
a web interface
A web browser is an excellent interface between a human and a computer. There is not a huge amount you can do to get information out of a human using a web browser. It's nice and simple to get your head round.
A web browser that displays a form for you to fill out, such as a login box, is called a thin client. A GUI application that displays a form for you to fill out, such as a spreadsheet, usually has a lot more business logic built into it. This is called a thick client. People who ruin the simplicity of a web browser by shoehorning complex applications into it call their abomination a rich client.
what it isn't
where it is
history
