The User interface or Human Computer Interface is the way of means by which people-the users -interact with the system-a particular machine, device, computer.

The user interface provides means of:

• Input, allowing the users to manipulate a system
• Output, allowing the system to produce the effects of the users manipulation.

Currently the following Types of user interface are the most common:

• Graphical user interfaces (GUI) accept input via devices such as computer keyboard and mouse and provide graphical output on the computer monitor.

• Web-based user interfaces or web user interfaces (WUI) accept input and provide output by generating web pages which are transmitted via the internet and viewed by the user using a web browser program.

• Command line interfaces, where the user provides the input by typing a command string with the computer keyboard and the system provides output by printing text on the computer monitor. Used for system administration tasks etc.

• Tactile interfaces supplement or replace other forms of output with feedback methods. Used in computerized simulators etc.

• Touch interfaces are graphical user interfaces using a touch screen display as a combined input and output device. Used in many types of industrial processes and machines, self-service machines etc.

Other types of user interfaces:

• Attentive user interfaces manage the user attention deciding when to interrupt the user, the kind of warnings, and the level of detail of the messages presented to the user.

• Batch interfaces are non-interactive user interfaces, where the user specifies all the details of the batch job in advance to batch processing, and receives the output when all the processing is done. The computer does not prompt for further input after the processing has started.

• Conversational Interface Agents attempt to personify the computer interface in the form of an animated person, robot, or other character, and present interactions in a conversational form.

• Crossing-based interfaces are graphical user interfaces in which the primary task consists in crossing boundaries instead of pointing.

• Intelligent user interfaces are human-machine interfaces that aim to improve the efficiency, effectiveness, and naturalness of human-machine interaction by representing, reasoning, and acting on models of the user, domain, task, discourse, and media (e.g., graphics, natural language, gesture).

• Live user interfaces utilize the power of human interaction to leverage the user interface. With a LUI, a computer representation of a live customer service representative could navigate with the user through the interface, and present images, maps and video clips from within the website. The computer representation can also help the user perform on-line purchases and complete complex forms.

• Multi-screen interfaces, employ multiple displays to provide a more flexible interaction. This is often employed in computer game interaction in both the commercial arcades and more recently the handheld markets.

• Noncommand user interfaces, which observe the user to infer his / her needs and intentions, without requiring that he / she formulate explicit commands.

• Reflexive user interfaces where the users control and redefine the entire system via the user interface alone, for instance to change its command verbs. Typically this is only possible with very rich graphic user interfaces.

• Tangible user interfaces, which place a greater emphasis on touch and physical environment or its element.

• Text user Interfaces are user interfaces which output text, but accept other form of input in addition to or in place of typed command strings.

• Voice user interfaces, which accept input and provide output by generating voice prompts which are transmitted via a telephone network and heard by the user using a telephone. The user input is made by pressing telephone keys.

• Natural-Language interfaces - Used for search engines and on webpages such as IKEA. User types in a question and waits for a response.

• Zero-Input interfaces get inputs from a set of sensors instead of querying the user with input dialogs.

• Zooming interfaces are graphical user interfaces in which information objects are represented at different levels of scale and detail, and where the user can change the scale of the viewed area in order to show more detail.

CLI (COMMAND LINE INTERFACE):

Command Line Interface (CLI) is a mechanism for interacting with a computer operating system or software by typing commands to perform specific tasks.

This method of instructing a computer to perform a given task is referred to as "entering" a command: the system waits for the user to conclude the submitting of the text command by pressing the "Enter" key (a descendant of the "carriage return" key of a typewriter keyboard).

A command line interpreter then receives, analyses, and launches the requested command. The command line interpreter may be run in a text terminal or in a terminal emulator window as a remote shell client such as PuTTY. Upon completion, the command usually returns output to the user in the form of text lines on the CLI. This output may be an answer if the command was a question, or otherwise a summary of the operation.

The CLI continues to improve with GUIs like those provided by Microsoft Windows ,MacOSand the X Window system,MacOS and the X Window system. In some applications, such as MATLAB, a CLI is integrated with the GUI, with the benefits of both.

A program that implements such a text interface is often called a command line interpreter or shell. Examples include the various Unix shells (sh, ksh, csh, tcsh, bash, etc.)

A user can specify relative or absolute paths to any command or data.

Examples of this include MS-DOS, Windows, and UNIX, which provide forms of a change directory command which allows access to any directory in the system. Protection of resources is provided by a system of resource ownership by privileged groups, and password-protected user accounts which are members of specific groups. MS-DOS provides no such resource protection.

Other CLIs (such as those in routers) limit the set of commands that a user can perform to a subset, determined by location within a command hierarchy, grouped by association with security, system, interface, etc. The location within this hierarchy and the options available are often referred to as a mode. In these systems the user might traverse through a series of sub-hierarchies, each with their own subset of commands.

For example, if the CLI had two modes called interface and system, the user would enter the word ’interface’ at the command prompt and then enter an interface mode, where a certain subset of commands and data are available. At this point system commands are not accessible and would not be accessible until the user explicitly exits the interface mode.

A command prompt (or just prompt) is a sequence of (one or more) characters used in a command line interface to indicate readiness to accept commands. Its intent is to literally prompt the user to take action. A prompt usually ends with one of the characters $, %, #, :, > and often includes other information, such as the path of the current working directory.

It is common for prompts to be modifiable by the user. Depending on the environment, they may include colors, special characters, and other elements like the current time, in order, for instance, to make the prompt more informative or visually pleasing, to distinguish sessions on various machines, or to indicate the current level of nesting of commands.

This contrasts with the use of a mouse pointer with a graphical user interface (GUI) to click on options, or menus on a Text user interface (TUI) to select options.

GUI:GRAPHICAL USER INTERFACE :

Graphical user interface (GUI) is a type ofuser interface which allows people to interact with electronic devices like computers, hand-held devices (MP3 Players, Portable Media Players, Gaming devices), household appliances and office equipment. A GUI offers graphical icons, and visual indicators as opposed to text-based interfaces interfaces, typed command labels or text navigation to fully represent the information and actions available to a user. The actions are usually performed through direct manipulation of the graphical elements.

A GUI uses a combination of technologies and devices to provide a platform the user can interact with, for the tasks of gathering and producing information. The most common combination in GUIs is the WIMP paradigm, especially in personal computers.

This style of interaction uses a physical input device to control the position of a cursor and presents information organized in windows and represented with icons. Available commands are compiled together in menus and actioned through the pointing device. A window manager facilitates the interactions between windows, applications, and the windowing system. The windowing system handles hardware devices such as pointing devices and graphics hardware, as well as the positioning of the cursor.

In personal computers all these elements are modelled through a desktop metaphor, to produce a simulation called a desktop environment in which the display represents a desktop, upon which documents and folders of documents can be placed. Window managers and other software combine to simulate the desktop environment with varying degrees of realism.

GUIs were introduced in reaction to the steep learning curve of (CLI), which require commands to be typed on the keyboard. Since the commands available in command line interfaces can be numerous, complicated operations can be completed using a short sequence of words and symbols. This allows for greater efficiency and productivity once many commands are learned but reaching this level takes some time because the command words are not easily discoverable. WIMPs ("window, icon, menu, pointing device"), on the other hand, present the user with numerous widgets that represent and can trigger some of the system’s available commands.

WIMPs extensively use modes as the meaning of all keys and clicks on specific positions on the screen are redefined all the time. Command line interfaces use modes only in limited forms, such as the current directory and environment variables.

Most modern operating systems provide both a GUI and some level of a CLI, although the GUIs usually receive more attention. The GUI is usually WIMP-based, although occasionally other metaphors surface, such as those used in Microsoft Bob,3dwm or File System Visualizer (FSV).

Applications may also provide both interfaces, and when they do the GUI is usually a WIMP wrapper around the command-line version. This is especially common with applications designed for Unix-like operating systems. The latter used to be implemented first because it allowed the developers to focus exclusively on their product’s functionality without bothering about interface details such as designing icons and placing buttons. Designing programs this way also allows users to run the program non-interactively, such as in a shell script.