Following are some of the important input devices which are used in a computer −
Keyboard
Keyboard is the most common and very popular input device which helps to input data to the computer. The layout of the keyboard is like that of traditional typewriter, although there are some additional keys provided for performing additional functions.
Keyboards are of two sizes 84 keys or 101/102 keys, but now keyboards with 104 keys or 108 keys are also available for Windows and Internet.
The keys on the keyboard are as follows −
Mouse
Mouse is the most popular pointing device. It is a very famous cursor-control device having a small palm size box with a round ball at its base, which senses the movement of the mouse and sends corresponding signals to the CPU when the mouse buttons are pressed.
Generally, it has two buttons called the left and the right button and a wheel is present between the buttons. A mouse can be used to control the position of the cursor on the screen, but it cannot be used to enter text into the computer.
Advantages
Joystick
Joystick is also a pointing device, which is used to move the cursor position on a monitor screen. It is a stick having a spherical ball at its both lower and upper ends. The lower spherical ball moves in a socket. The joystick can be moved in all four directions.
The function of the joystick is similar to that of a mouse. It is mainly used in Computer Aided Designing (CAD) and playing computer games.
Light Pen
Light pen is a pointing device similar to a pen. It is used to select a displayed menu item or draw pictures on the monitor screen. It consists of a photocell and an optical system placed in a small tube.
When the tip of a light pen is moved over the monitor screen and the pen button is pressed, its photocell sensing element detects the screen location and sends the corresponding signal to the CPU.
Track Ball
Track ball is an input device that is mostly used in notebook or laptop computer, instead of a mouse. This is a ball which is half inserted and by moving fingers on the ball, the pointer can be moved.
Since the whole device is not moved, a track ball requires less space than a mouse. A track ball comes in various shapes like a ball, a button, or a square.
Scanner
Scanner is an input device, which works more like a photocopy machine. It is used when some information is available on paper and it is to be transferred to the hard disk of the computer for further manipulation.
Scanner captures images from the source which are then converted into a digital form that can be stored on the disk. These images can be edited before they are printed.
Digitizer
Digitizer is an input device which converts analog information into digital form. Digitizer can convert a signal from the television or camera into a series of numbers that could be stored in a computer. They can be used by the computer to create a picture of whatever the camera had been pointed at.
Digitizer is also known as Tablet or Graphics Tablet as it converts graphics and pictorial data into binary inputs. A graphic tablet as digitizer is used for fine works of drawing and image manipulation applications.
Microphone
Microphone is an input device to input sound that is then stored in a digital form.
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The microphone is used for various applications such as adding sound to a multimedia presentation or for mixing music.
Magnetic Ink Card Reader (MICR)
MICR input device is generally used in banks as there are large number of cheques to be processed every day. The bank's code number and cheque number are printed on the cheques with a special type of ink that contains particles of magnetic material that are machine readable.
This reading process is called Magnetic Ink Character Recognition (MICR). The main advantages of MICR is that it is fast and less error prone.
Optical Character Reader (OCR)
OCR is an input device used to read a printed text.
Input Devices
OCR scans the text optically, character by character, converts them into a machine readable code, and stores the text on the system memory.
Bar Code Readers
Bar Code Reader is a device used for reading bar coded data (data in the form of light and dark lines). Bar coded data is generally used in labelling goods, numbering the books, etc. It may be a handheld scanner or may be embedded in a stationary scanner.
Bar Code Reader scans a bar code image, converts it into an alphanumeric value, which is then fed to the computer that the bar code reader is connected to.
Optical Mark Reader (OMR)
OMR is a special type of optical scanner used to recognize the type of mark made by pen or pencil. It is used where one out of a few alternatives is to be selected and marked.
It is specially used for checking the answer sheets of examinations having multiple choice questions.
The computing literature often draws a sharp distinction between input and output; computer scientists are used to regarding a screen as a passive output device and a mouse as a pure input device. However, nearly all examples of human-computer interaction require both input and output to do anything useful. For example, what good would a mouse be without the corresponding feedback embodied by the cursor on the screen, as well as the sound and feel of the buttons when they are clicked? The distinction between output devices and input devices becomes even more blurred in the real world. A sheet of paper can be used to both record ideas (input) and display them (output). Clay reacts to the sculptor’s fingers yet also provides feedback through the curvature and texture of its surface. Indeed, the complete and seamless integration of input and output is becoming a common research theme in advanced computer interfaces such as ubiquitous computing (Weiser, 1991) and tangible interaction (Ishii & Ullmer, 1997).
Input and output bridge the chasm between a computer’s inner world of bits, and the real world perceptible to the human senses. Input to computers consists of sensed information about the physical environment. Familiar examples include the mouse, which senses movement across a surface, and the keyboard, which detects a contact closure when the user presses a key. However, any sensed information about physical properties of people, places, or things can serve as input to computer systems. Output from computers can comprise any emission or modification to the physical environment, such as a display (including the cathode ray tube (CRT), flat-panel displays, or even light emitting diodes), speakers, or tactile and force feedback devices (sometimes referred to as haptic displays). An interaction technique is the fusion of input and output, consisting of all hardware and software elements, that provides a way for the user to accomplish a low-level task. For example, in the traditional graphical user interface, users can scroll through a document by clicking or dragging the mouse (input) within a scroll bar displayed on the screen (output).
Input and output bridge the chasm between a computer’s inner world of bits, and the real world perceptible to the human senses. Input to computers consists of sensed information about the physical environment. Familiar examples include the mouse, which senses movement across a surface, and the keyboard, which detects a contact closure when the user presses a key. However, any sensed information about physical properties of people, places, or things can serve as input to computer systems. Output from computers can comprise any emission or modification to the physical environment, such as a display (including the cathode ray tube (CRT), flat-panel displays, or even light emitting diodes), speakers, or tactile and force feedback devices (sometimes referred to as haptic displays). An interaction technique is the fusion of input and output, consisting of all hardware and software elements, that provides a way for the user to accomplish a low-level task. For example, in the traditional graphical user interface, users can scroll through a document by clicking or dragging the mouse (input) within a scroll bar displayed on the screen (output).
Introduction: -
In computing, input/output, or I/O, refers to the communication between an information processing system (such as a computer), and the outside world possibly a human, or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it. The term can also be used as part of an action; to 'perform I/O' is to perform an input or output operation. I/O devices are used by a person (or other system) to communicate with a computer. a keyboard or a mouse may be an input device for a computer, while monitor sand printers are considered output devices for a computer. Devices for communication between computers, such as modems and network cards, typically serve for both input and output. Goals for I/O • Users should access all devices in a uniform manner. • Devices should be named in a uniform manner. • The OS, without the intervention of the user program, should handle recoverable errors. • The OS must maintain security of the devices. • The OS should optimize the performance of the I/O system. Input and output operation in operating system:- In computer architecture, the combination of the CPU and main memory (i.e. memory that the CPU can read and write to directly, with individual instructions) is considered the brain of a computer, and from that point of view any transfer of information from or to that combination, for example to or from a disk drive, is considered I/O. The CPU and its supporting circuitry provide memory-mapped I/O that is used in low-level computer programming in the implementation of device drivers. An I/O algorithm is one designed to exploit locality and perform efficiently when data reside on secondary storage, such as a disk drive. Input/output memory-mapped in o/s:- The CPU and its supporting circuitry provide memory-mapped I/O that is used in low-level computer programming in the implementation of device drivers. An I/O algorithm is one designed to exploit locality and perform efficiently when data reside on secondary storage, such as a disk drive. Input/output port-mapped in o/s:- Port-mapped I/O usually requires the use of instructions which are specifically designed to perform I/O operations. Interaction b/w user and i/o:- . The output from these devices is input for the computer. Similarly, printers and monitors take as input signals that a computer outputs. They then convert these signals into representations that human users can see or read. For a human user the process of reading or seeing these representations is receiving input. These interactions between computers and humans is studied in a field called human–computer interaction. i/o procedure:- A user process requesting I/O makes a call in the form:-DOIO(stream, mode, amount, destination, semaphores) Where DOIO is the name of the relevant I/O procedure stream:- is the ident no. of the stream on which I/O is to take place mode:- operation required,- input, output, scan, etc,- may indicate char code too amount: how much data to be transferred.destination (source): memory area where data is to be transferred to/from semaphore: address of semaphore 'request serviced' to be signaled by the device handler when I/O operation is complete. Input /Output (I/O) Management in o/s So far we have studied how resources like processor and main memory are managed. We shall now examine the I/O management. Humans interact with machines by providing information through IO devices. Also, much of whatever a computer system provides as on-line services is essentially made available through specialized devices such as screen displays, printers, keyboards, mouse, etc. Clearly, management of all these devices can affect the throughput of a system. For this reason, input output management also becomes one of the primary responsibilities of an operating system. In this chapter we shall examine the role of operating systems in managing IO devices. In particular, we shall examine how the end use of the devices determines the way they are regulated for communication with either humans or with systems. Issues in I/O Management Let us first examine the context of input output in a computer system. We shall look at issues initially from the point of view of communication with a device. Later, we shall also examine issues from the point of view of managing events. When we analyze device communication, we notice that communication is required at the following three levels: ? The need for a human to input information and receive output from a computer. ? The need for a device to input information and receive output from a computer. ? The need for computers to communicate (receive/send information) over networks. The first kind of IO devices operate at rates good for humans to interact. These may be character-oriented devices like a keyboard or an event-generating device like a mouse. Usually, human input using a key board will be a few key depressions at a time. This means that the communication is rarely more than a few bytes. Also, the mouse events can be encoded by a small amount of information (just a few bytes). Even though a human input is very small, it is stipulated that it is very important, and therefore requires an immediate response from the system. A communication which attempts to draw attention often requires the use of an interrupt mechanism or a programmed data mode of operation. Interrupt as well as programmed data mode of IO shall be dealt with in detail later in this chapter. Managing Events Our next observation is that a computer system may sometimes be embedded to interact with a real-life activity or process. It is quite possible that in some operational context a process may have to synchronize with some other process. In such a case this process may actually have to wait to achieve a rendezvous with another process. In fact, whichever of the two synchronizing processes arrives first at the point of rendezvous would have to wait. When the other process also reaches the point of synchronization, the first process may proceed after recognizing the synchronizing event. Note that events may be communicated using signals which we shall learn about later. In some other cases a process may have to respond to an asynchronous event that may occur at any time. Usually, an asynchronous input is attended to in the next instruction cycle as we saw In fact, the OS checks for any event which may have occurred in the intervening period. This means that an OS incorporates some IO event recognition mechanism. IO handling mechanisms may be like polling, or a programmed data transfer, or an interrupt mechanism, or even may use a direct memory access (DMA) with cycle stealing. We shall examine all these mechanisms in some detail The unit of data transfer may either be one character at a time or a block of characters. It may require to set up a procedure or a protocol. This is particularly the case when a Programmed Data Mode In this mode of communication, execution of an IO instruction ensures that a program shall not advance till it is completed. To that extent one is assured that IO happens before anything else happens. As depicted in Figure 5.1, in this mode an IO instruction is issued to an IO device and the program executes in “busy-waiting” (idling) mode till the IO is completed. During the busy-wait period the processor is continually interrogating to check if the device has completed IO. Invariably the data transfer is accomplished through an identified register and a flag in a processor. Polling In this mode of data transfer, shown in Figure 5.2, the system interrogates each device in turn to determine if it is ready to communicate. If it is ready, communication is initiated and subsequently the process continues again to interrogate in the same sequence. This is just like a round-robin strategy. Each IO device gets an opportunity to establish Communication in turn. No device has a particular advantage (like say a priority) over other devices. Polling is quite commonly used by systems to interrogate ports on a network. Polling may also be scheduled to interrogate at some pre-assigned time intervals. It should be remarked here that most daemon software operate in polling mode. Essentially In hardware, this may typically translate to the following protocol: 1.Assign a distinct address to each device connected to a bus. 2. The bus controller scans through the addresses in sequence to find which device wishes to establish a communication. 3. Allow the device that is ready to communicate to leave its data on the register. 4. The IO is accomplished. In case of an input the processor picks up the data. In case of an output the device picks up the data. 5. Move to interrogate the next device address in sequence to check if it is ready to communicate. Interrupt Mode Let us begin with a simple illustration to explain the basic rationale behind interrupt mode of data transfer. Suppose a program needs input from a device which communicates using interrupt. Even with the present-day technology the devices are one thousand or more times slower than the processor. So if the program waits on the input device it would cycle through many processor cycles just waiting for the input device to be ready to communicate. This is where the interrupt mode of communication scores. To begin with, a program may initiate IO request and advance without suspending its operation. At the time when the device is actually ready to establish an IO, the device raises an interrupt to seek communication. Immediately the program execution is suspended temporarily and current state of the process is stored. The control is passed on to an interrupt service routine (which may be specific to the device) to perform the desired input. Subsequently, the suspended process context is restored to resume the program from the point of its suspension. device drive initiates i/o initiates i/o cpu receiving interrupt transfer Input ready output complete or error interrupt signal Interrupt handler processes data CPU resumes processing Internal Interrupt: The source of interrupt may be a memory resident process or a function from within the processor. We regard such an interrupt as an internal interrupt. A processor malfunction results in an internal interrupt. An attempt to divide by zero or execute an illegal or non-existent instruction code results in an internal interrupt as well. A malfunction arising from a division by zero is called a trap. Internal interrupt may be caused by a timer as well. This may be because either the allocated processor time slice to a process has elapsed or for some reason the process needs to be pre-empted. Note that an RTOS may pre-empt a running process by using an interrupt to ensure that the stipulated response time required is met. This would also be a case of internal interrupt. External Interrupt: If the source of interrupt in not internal, i.e. it is other than a process or processor related event then it is an external interrupt. This may be caused by a device which is seeking attention of a processor. As indicated earlier, a program may seek an IO and issue an IO command but proceed. After a while, the device from which IO was sought is ready to communicate. In that case the device may raise an interrupt. This would be a case of an external interrupt. Software Interrupt: Most OSs offer two modes of operation, the user mode and the system mode. Whenever a user program makes a system call, be it for IO or a special service, the operation must have a transition from user mode to system mode. An interrupt is raised to effect this transition from user to system mode of operation. Such an interrupt is called a software interrupt. We shall next examine how an interrupt is serviced. Suppose we are executing an instruction at i in program P when interrupt signal has been raised. Let us also assume that we have an interrupt service routine which is to be initiated to service the interrupt. The following steps describe how a typical interrupt service may happen. DMA (Direct memory access)Mode of Data Transfer This is a mode of data transfer in which IO is performed in large data blocks. For instance, the disks communicate in data blocks of sizes like 512 bytes or 1024 bytes. The direct memory access, or DMA ensures access to main memory without processor intervention or support. Such independence from processor makes this mode of transfer extremely efficient. When a process initiates a direct memory access (DMA) transfer, its execution is briefly suspended (using an interrupt) to set up the DMA control. The DMA control requires the information on starting address in main memory and size of data for transfer. This information is stored in DMA controller. Following the DMA set up, the program resumes from the point of suspension. The device communicates with main memory stealing memory access cycles in competition with other devices and processor. of disk to main memory transfer in DMA mode. We first note that there is a disk controller to regulate communication from one or more disk drives. This controller essentially isolates individual devices from direct communication with the CPU or main memory. The communication is regulated to first happen between the device and the controller, and later between the controller and main memory or CPU if so needed. Note that these devices communicate in blocks of bits or bytes as a data stream. Clearly, an unbuffered communication is infeasible via the data bus. The bus has its own timing control protocol. . Once the controller buffer has the required data, then one can envisage to put the controller in contention with CPU and main memory or CPU to obtain an access to the bus. Thus if the controller can get the bus then by using the address and data bus it can directly communicate with main memory. This transfer shall be completely independent of program control from the processor mem i/o Hardware IO management requires that a proper set-up is created by an application on computer system with an IO device. An IO operation is a combination of HW and SW instructions as shown in Figure Following the issuance of an IO command, OS kernel resolves it, and then communicates Principles of I/O Hardware Handling Interrupt Using Device Drivers Let us assume we have a user process which seeks to communicate with an input device using a device driver process. Processes communicate by signaling. The steps describe the complete operational sequence (with corresponding numbers). 1. Register with listener chain of the driver: The user process P signals the device driver as process DD to register its IO request. Process DD maintains a list data structure, basically a listener chain, in which it registers requests received from processes which seek to communicate with the input device. 2. Enable the device: The process DD sends a device enable signal to the device. Some Additional Points In this section we discuss a few critical services like clocks and spooling. We also discuss many additional points relevant to IO management like caches. Spooling: Suppose we have a printer connected to a machine. Many users may seek to use the printer. To avoid print clashes, it is important to be able to queue up all the print requests. This is achieved by spooling. The OS maintains all print requests and schedules each users' print requests. In other words, all output commands to print are intercepted by the OS kernel. An area is used to spool the output so that a users' job does not have to wait for the printer to be available. One can examine a print queue status by using lpq and lpstat commands in Unix. Clocks : The CPU has a system clock. The OS uses this clock to provide a variety of system- and application-based services. For instance, the print-out should display the date and time of printing. Below we list some of the common clock-based services. ? Maintaining time of day. (Look up date command under Unix.) ? Scheduling a program run at a specified time during systems' operation. (Look up at and cron commands under Unix.) ? Preventing overruns by processes in preemptive scheduling. Note that this is important for real-time systems. In RTOS one follows a scheduling policy like the earliest deadline first. This policy may necessitate preemption of a running process. ? Keeping track of resource utilization or reserving resource use. ? Performance related measurements (like timing IO, CPU activity). Addressing a device: Most OSs reserve some addresses for use as exclusive addresses for devices. A system may have several DMA controllers, interrupt handling cards (for some process control), timers, serial ports (for terminals) or terminal concentrators, parallel ports (for printers), graphics controllers, or floppy and CD ROM drives, etc. A fixed range of addresses allocated to each of these devices. This ensures that the device drives communicate with the right ports for data. Caching: A cache is an intermediate level fast storage. Often caches can be regarded as fast buffers. These buffers may be used for communication between disk and memory or memory and CPU. The CPU memory caches may used for instructions or data. In case cache is used for instructions, then a group of instructions may be pre-fetched and kept there. This helps in overcoming the latency experienced in instruction fetch. In the same manner, when it is used for data it helps to attain a higher locality of reference. As for the main memory to disk caches, one use is in disk rewrites. The technique is used almost always to collect all the write requests for a few seconds before actually a disk is written into. Caching is always used to enhance the performance of systems. I/O channels: An IO channel is primarily a small computer to basically handle I/O from multiple sources. It ensures that I/O traffic is smoothed out. OS and CDE: The common desk top environment (CDE) is the norm now days. An OS provides some terminal-oriented facilities for operations in a CDE. In particular the graphics user interface (GUI) within windows is now a standard facility. The kernel I/O system recognizes all cursor and mouse events within a window to allow a user to bring windows up, iconize, scroll, reverse video, or even change font and control display. The I/O kernel provides all the screen management functions within the framework of a CDE. I/O Buffering • Instead of reading or writing data directly from the user’s memory, it is copied to or from an OS buffer • Reasons for buffering – Processes must wait for I/O to complete before proceeding – Certain pages must remain in main memory during I/O Single Buffer • Operating system assigns a buffer in main memory for an I/O request • Block-oriented – Input transfers made to buffer – Block moved to user space when needed – Another block is moved into the buffer Double Buffer • Use two system buffers instead of one • A process can transfer data to or from one buffer while the operating system empties or fills the other buffer • More than two buffers can be used for circular buffering Levels of I/O • User program • User level I/O functions • Device-independent OS software • Device drivers • Interrupt handlers
An output device is any peripheral that receives data from a computer, usually for display, projection, or physical reproduction. For example, the image shows an inkjet printer, an output device that can make a hard copy of any information shown on your monitor, which is another example of an output device. Monitors and printers are two of the most common output devices used with a computer.
![]() Types of output devices
The following list contains many different output devices. For further information, select any of the listings with blue text.
Drives such as a CD-ROM, DVD, floppy diskette drive, and USB flash drive are also considered storage devices.
What are the output devices of my computer
Every computer has a monitor or display screen, a sound card (or on-board sound on the motherboard), and a video card (or on-board video on the motherboard), which are all output devices. A printer is also very commonly used with computers. Depending on the type of computer and how the computer is used, other output devices may be used with a computer. The best method of determining all of the output devices your computer has is to go through the list above.
Why do computers need output devices?
A computer can still work without an output device. However, without an output device, you'd have no way of determining what the computer is doing, if there are errors, or if it needs additional input. For example, you can disconnect your monitor from your computer, and it will still function, but it's not going to be very useful.
Related output device pages
Hardware terms, Input device, Input/output device, Output, Printing terms, Video terms
A common computer input device, a keyboard. A user presses a key which transfers information to a computer.
In computing, an input device is a piece of computer hardware equipment used to provide data and control signals to an information processing system such as a computer or information appliance. Examples of input devices include keyboards, mouse, scanners, digital cameras, joysticks, and microphones.
Input devices can be categorized based on:
Keyboard[edit]Input And Output Devices Examples
'Keyboards' are a human interface device which is represented as a layout of buttons. Each button, or key, can be used to either input a linguistic character to a computer, or to call upon a particular function of the computer. They act as the main text entry interface for most users. Traditional keyboards use spring-based buttons, though newer variations employ virtual keys, or even projected keyboards. It is typewriter like device composed of a matrix of switches.There also happens to be another keyboard that is like an input device for musical instrument which helps to produce sound.
Examples of types of keyboards include:
Mouse[edit]
A computer mouse
Pointing devices are the most commonly used input devices today. A pointing device is any human interface device that allows a user to input spatial data to a computer. In the case of mouse and touchpads, this is usually achieved by detecting movement across a physical surface. Analog devices, such as 3D mice, joysticks, or pointing sticks, function by reporting their angle of deflection. Movements of the pointing device are echoed on the screen by movements of the pointer, creating a simple, intuitive way to navigate a computer's graphical user interface (GUI).
Pointing devices, which are input devices used to specify a position in space, can further be classified according to:
For pointing devices, direct input is almost necessarily absolute, but indirect input may be either absolute or relative. For example, digitizing graphics tablets that do not have an embedded screen involve indirect input and sense absolute positions and are often run in an absolute input mode, but they may also be set up to simulate a relative input mode like that of a touchpad, where the stylus or puck can be lifted and repositioned. Embeded LCD tablets which are also referred to as graphics tablet monitor is the extension of digitizing graphics tablets. It enables users to see the real-time positions via the screen while using.
Examples of types of pointing devices include:
High-degree of freedom input devices[edit]
Some devices allow many continuous degrees of freedom as input. These can be used as pointing devices, but are generally used in ways that don't involve pointing to a location in space, such as the control of a camera angle while in 3D applications. These kinds of devices are typically used in virtual reality systems (CAVEs), where input that registers six degrees of freedom is required.
Composite devices[edit]
Wii Remote with attached strap
Input devices, such as buttons and joysticks, can be combined on a single physical device that could be thought of as a composite device. Many gaming devices have controllers like this. Technically mice are composite devices, as they both track movement and provide buttons for clicking, but composite devices are generally considered to have more than two different forms of input.
Examples of types of composite devices include:
Video input devices[edit]
Microsoft Kinect sensor, works by detecting human motion visually
Project On Input And Output Devices Worksheet
Video input devices are used to digitize images or video from the outside world into the computer. The information can be stored in a multitude of formats depending on the user's requirement.
Examples of types of a video input devices include:
Audio input devices[edit]
Audio input devices are used to capture sound. In some cases, an audio output device can be used as an input device, in order to capture produced sound. Audio input devices allow a user to send audio signals to a computer for processing, recording, or carrying out commands. Devices such as microphones allow users to speak to the computer in order to record a voice message or navigate software. Aside from recording, audio input devices are also used with speech recognition software.
Examples of types of audio input devices include:
Punched paper[edit]
Punched cards and punched tapes were much used in the 20th century. A punched hole represented a one; its absence represented a zero. There were mechanical and optical readers.
Other[edit]See also[edit]Further reading[edit]
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