Working of I/O system

"Working of I/O System"

The working of I/O system combines I/O hardware and I/O software. The I/O hardware includes ports, buses and device controllers for different devices, and I/O devices. The I/O software is the device driver software that may be embedded with operating system or comes with each device. The working of I/O system is described as follows—

• I/O Devices are attached to computer via the ports of computer. There are many standard ports available on the backside of the computer case like serial port and parallel port. If one or more devices use a common set of wires, it is called a bus. For example, PCI bus, PCI Express bus, etc.
• Device Controller operates on a bus, a port or a device. It controls the signals on the wires of port or bus. The controllers have one or more registers for data and control signals. Controller may be simple like a serial port controller for a serial port, or, complex like a SCSI controller. Some devices have their own built-in controllers.
• Device Driver is software via which the operating system communicates with the device controllers. Each device has its own device driver, and a device controller which is specific to the device. The device drivers hide the differences among the different device controller and present a uniform interface to the operating system.

APPLICATION OF I/O DEVICE:

• Application programs use an I/O device by issuing commands and exchanging data with the device driver.
•  The device driver provides correct commands to the controller, interprets the controller register, and transfers data to and from device controller registers as required for the correct device operation.

introduction of input and output devices

 Introduction of input and output devices:

• A computer interacts with the external environment via the input-output (I/O) devices attached to it.
•  Input device is used for providing data and instructions to the computer.
•  After processing the input data, computer provides output to the user via the output device.
•  The I/O devices that are attached, externally, to the computer machine are also called peripheral devices.
•  Different kinds of input and output devices are used for different kinds of input and output requirements.

Input and output devices

"INPUT AND OUTPUT DEVICES" Input-output unit—Input unit, output unit Input devices—Human data entry devices, source data entry devices Human data entry devices Keyboard Pointing devices—Mouse, trackball, joystick, digitizing tablet Pick devices—Light pen, touch screen Source data entry devices Audio input device (microphone, sound card, speech recognition) Video input device (video camera, digital camera) Optical input devices—Scanner (hand held, flat bed), OCR, MICR, OMR, barcode reader Output devices—Hard copy devices, soft copy devices Hard copy devices Printer—Impact printers (dot matrix, daisy wheel, drum), non-impact printers (ink-jet, laser) Plotter—Drum plotter, flatbed plotter Computer output on microfilm (microfiche) Soft copy devices—Monitor, visual display terminal, video output, audio response (speakers, headphone) I/O port—Parallel port, serial port, USB port, firewire port Working of I/O system—I/O devices, device controller, device driver

the computer system

 The Computer System:

Computer is an electronic device that accepts data as input, processes the input data by performing mathematical and logical operations on it, and gives the desired output. The computer system consists of four parts—(1) Hardware, (2) Software, (3) Data, and (4) Users.

Hardware consists of the mechanical parts that make up the computer as a machine. The hardware consists of physical devices of the computer. The devices are required for input, output, storage and processing of the data. Keyboard, monitor, hard disk drive, floppy disk drive, printer, processor and motherboard are some of the hardware devices.

Software is a set of instructions that tells the computer about the tasks to be performed and how these tasks are to be performed.Program is a set of instructions, written in a language understood by the computer, to perform a specific task. A set of programs and documents are collectively called software. The hardware of the computer system cannot perform any task on its own. The hardware needs to be instructed about the task to be performed. Software instructs the computer about the task to be performed. The hardware carries out these tasks. Different software can be loaded on the same hardware to perform different kinds of tasks.

Data are isolated values or raw facts, which by themselves have no much significance. For example, the data like 29, January, and1994 just represent values. The data is provided as input to the computer, which is processed to generate some meaningful information. For example, 29, January and 1994 are processed by the computer to give the date of birth of a person.

Users are people who write computer programs or interact with the computer. They are also known as skinware, liveware, humanware or peopleware. Programmers, data entry operators, system analyst and computer hardware engineers fall into this category.

The Input-Process-Output Concept

A computer is an electronic device that (1) accepts data, (2) processes data, (3) generates output, and (4) stores data. The concept of generating output information from the input data is also referred to as input-process-output concept.

The input-process-output concept of the computer is explained as follows—

• Input The computer accepts input data from the user via an input device like keyboard. The input data can be characters, word, text, sound, images, document, etc.
• Process The computer processes the input data. For this, it performs some actions on the data by using the instructions or program given by the user of the data. The action could be an arithmetic or logic calculation, editing, modifying a document, etc. During processing, the data, instructions and the output are stored temporarily in the computer’s main memory.
• Output The output is the result generated after the processing of data. The output may be in the form of text, sound, image, document, etc. The computer may display the output on a monitor, send output to the printer for printing, play the output, etc.
• Storage The input data, instructions and output are stored permanently in the secondary storage devices like disk or tape. The stored data can be retrieved later, whenever needed.

 Components of Computer Hardware:

The computer system hardware comprises of three main components:

1. Input/Output (I/O) Unit,
2. Central Processing Unit (CPU), and
3. Memory Unit.

The I/O unit consists of the input unit and the output unit. CPU performs calculations and processing on the input data, to generate the output. The memory unit is used to store the data, the instructions and the output information.  

• Input/Output Unit The user interacts with the computer via the I/O unit. The Input unit accepts data from the user and the Output unit provides the processed data i.e. the information to the user. The Input unit converts the data that it accepts from the user, into a form that is understandable by the computer. Similarly, the Output unit provides the output in a form that is understandable by the user. The input is provided to the computer using input devices like keyboard, trackball and mouse. Some of the commonly used output devices are monitor and printer.
• Central Processing Unit CPU controls, coordinates and supervises the operations of the computer. It is responsible for processing of the input data. CPU consists of Arithmetic Logic Unit (ALU) and Control Unit (CU).
  • ALU performs all the arithmetic and logic operations on the input data.
  • CU controls the overall operations of the computer i.e. it checks the sequence of execution of instructions, and, controls and coordinates the overall functioning of the units of computer.
  Additionally, CPU also has a set of registers for temporary storage of data, instructions, addresses and intermediate results of calculation.
• Memory Unit Memory unit stores the data, instructions, intermediate results and output, temporarily, during the processing of data. This memory is also called the main memory or primary memory of the computer. The input data that is to be processed is brought into the main memory before processing. The instructions required for processing of data and any intermediate results are also stored in the main memory. The output is stored in memory before being transferred to the output device. CPU can work with the information stored in the main memory. Another kind of storage unit is also referred to as the secondary memory of the computer. The data, the programs and the output are stored permanently in the storage unit of the computer. Magnetic disks, optical disks and magnetic tapes are examples of secondary memory.