COA- Unit -5 Peripheral DeviceS

 

A peripheral device, also sometimes called an auxiliary device, is any connected device (internal or external) that provides a computer with additional functionality.

There are three types of peripherals:

Input peripherals: Allows user input, from the outside world to the computer. Example: Keyboard, Mouse etc.

Output peripherals: Allows information output, from the computer to the outside world. Example: Printer, Monitor etc

Input-Output peripherals: Allows both input(from outside world to computer) as well as, output(from computer to the outside world). Example: Touch screen etc.

10 Examples of Peripheral Devices

Mouse, Keyboard, Webcam, Microphone, Monitor, Speakers, Projector, Printer

USB Flash Drive

External Hard Drive

Input Devices

In computing, an input device is a peripheral (piece of computer hardware equipment) used to provide data and control signals to an information processing system such as a computer or other information appliance. Examples of input devices include

keyboards, mice, scanners, digital cameras and joysticks.

Output Devices

An output device is any piece of computer hardware equipment used to communicate the results of data processing carried out by an information processing system (such as a computer) which converts the electronically generated information into humanreadable form.

Interfaces

Interface is a shared boundary between two separate components of the computer system which can be used to attach two or more components to the system for communication purposes.

There are two types of interface:

CPU Interface

I/O Interface

Let's understand the I/O Interface in details,

Input-Output Interface

Peripherals connected to a computer need special communication links for interfacing with CPU. In computer system, there are special hardware components between the CPU and peripherals to control or manage the input-output transfers. These

components are called input-output interface

units because they provide communication links between processor bus and peripherals. They provide a method for

transferring information between internal system and input-output devices.

Input/Output Ports

A connection point that acts as interface between the computer and external devices like mouse, printer, modem, etc. is called port. Ports are of two

types -

Internal port - It connects the motherboard to

internal devices like hard disk drive, CD drive, internal modem, etc.

External port - It connects the motherboard to

external devices like modem, mouse, printer, flash drives, etc.

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Computer Organization Notes Unit -5 Serial Port

Serial ports transmit data sequentially one bit at a time. So they need only one wire to transmit 8 bits

Parallel Port

Parallel ports can send or receive 8 bits or 1 byte at a time. Parallel ports come in form of 25-pin female pins and are used to connect printer, scanner, external hard disk drive, etc.

USB Port

USB stands for Universal Serial Bus. It is the industry standard for short distance digital data connection. USB port is a standardized port to connect a variety of devices like printer, camera, keyboard, speaker, etc.

PS-2 Port

PS/2 stands for Personal System/2. It is a female 6-pin port standard that connects to the male mini-DIN cable. PS/2 was introduced by IBM to connect mouse and keyboard to personal computers.

Infrared Port

Infrared port is a port that enables wireless exchange of data within a radius of 10m. Two devices that have infrared ports are placed facing each other so that beams of infrared lights can be used to share data.

Bluetooth Port

Bluetooth is a telecommunication specification that facilitates wireless connection between phones, computers and other digital devices over short range wireless connection. Bluetooth port enables

synchronization between Bluetooth-enabled devices.

There are two types of Bluetooth ports -

Incoming - It is used to receive connection from

Bluetooth devices.

Outgoing - It is used to request connection to other

Bluetooth devices.

Modes of I/O Data Transfer

Data transfer between the central unit and I/O devices can be handled in generally three types of modes which are given below:

1. Programmed I/O

2. Interrupt Initiated I/O

3. Direct Memory Access

Programmed I/O

Programmed I/O instructions are the result of I/O instructions written in computer program. Each data item transfer is initiated by the instruction in the program.

Usually the program controls data transfer to and from CPU and peripheral. Transferring data under programmed I/O requires constant monitoring of the peripherals by the CPU.

Interrupt Initiated I/O

In the programmed I/O method the CPU stays in the program loop until the I/O unit indicates that it is ready for data transfer. This is time consuming process because it keeps the processor busy needlessly.

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Computer Organization Notes Unit -5

Direct Memory Access

Removing the CPU from the path and letting the peripheral device manage the memory buses directly would improve the speed of transfer. This technique is known as DMA.

In this, the interface transfer data to and from the memory through memory bus. A DMA controller manages to transfer data between peripherals and memory unit.

Many hardware systems use DMA such as disk drive controllers, graphic cards, network cards and sound cards etc. It is also used for intra chip data transfer in multicore processors.

Interrupts

Data transfer between the CPU and the peripherals is initiated by the CPU. But the CPU cannot start the transfer unless the peripheral is ready to communicate with the CPU. When a device is ready to communicate with the CPU, it generates

an interrupt signal. A number of input-output devices are attached to the computer and each device is able to generate an interrupt request.

Priority Interrupt

A priority interrupt is a system which decides the priority at which various devices, which generates the interrupt signal at the same time, will be serviced by the CPU. The system has authority to decide which conditions are allowed to interrupt the CPU, while some other interrupt is being serviced. Generally, devices with high speed transfer such as magnetic disks are given high priority and slow devices such as keyboards are given low priority.

Types of Interrupts:

Following are some different types of interrupts:

Hardware Interrupts

When the signal for the processor is from an external device or hardware then this interrupts is known as hardware interrupt.

Let us consider an example: when we press any key on our keyboard to do some action, then this pressing of the key will generate an interrupt signal for the processor to perform certain action.

Such an interrupt can be of two types:

Maskable Interrupt

The hardware interrupts which can be delayed when a much high priority interrupt has occurred at the same time.

Non Maskable Interrupt

The hardware interrupts which cannot be delayed and should be processed by the processor immediately.

Software Interrupts

The interrupt that is caused by any internal system of the computer system is known as a software interrupt. It can also be of two types:

Normal Interrupt

The interrupts that are caused by software instructions are called normal software interrupts.

Exception

Unplanned interrupts which are produced during the execution of some program are called exceptions, such as division by zero.

Daisy Chaining Priority

This way of deciding the interrupt priority consists of serial connection of all the devices which generates an interrupt signal. The device with the highest priority is placed at the first position followed by lower priority devices and the device which has lowest priority among all is placed at the last in the chain.

In daisy chaining system all the devices are connected in a serial form. The interrupt line request is common to all devices. If any device has interrupt signal in low level state then interrupt line goes to low level state and enables the interrupt input in the CPU. When there is no interrupt the interrupt line stays in high level state. The CPU respond to the interrupt by enabling the interrupt acknowledge line. This signal is received by

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the device 1 at its PI input. The acknowledge signal passes to next device through PO output only if device 1 is not requesting an interrupt.

instruction to initiate the channel program, the channel then assumes control of the I/O operations until they are completed.

IBM 370 I/O Channel

This problem can be overcome by using interrupt initiated I/O. In this when the interface determines that the peripheral is ready for data transfer, it generates an interrupt. After receiving the interrupt signal, the CPU stops the task which it is processing and service the I/O transfer and then returns back to its previous processing task.

Input/Output Channels

A channel is an independent hardware component that co-ordinate all I/O to a set of controllers. Computer systems that use I/O channel have special hardware components that handle all I/O operations.

Channels use separate, independent and low cost processors for its functioning which are called Channel Processors.

Each channel supports one or more controllers or devices. Channel programs contain list of commands to the channel itself and for various connected controllers or devices. Once the operating system has prepared a list of I/O commands, it executes a single I/O machine

The I/O processor in the IBM 370 computer is called a Channel. A computer system configuration includes a number of channels which are connected to one or more I/O devices.

Categories of I/O Channels

Following are the different categories of I/O channels:

Multiplexer

The Multiplexer channel can be connected to a number of slow and medium speed devices. It is capable of operating number of I/O devices simultaneously.

Selector

This channel can handle only one I/O operation at a time and is used to control one high speed device at a time.

Block-Multiplexer

It combines the features of both multiplexer and selector channels.

The CPU directly can communicate with the channels through control lines. Following diagram shows the word format of channel operation.

Input/Output Processor

An input-output processor (IOP) is a processor with direct memory access capability. In this, the computer system is divided into a memory unit and number of processors.

Each IOP controls and manage the input-output tasks. The IOP is similar to CPU except that it handles only the details of I/O processing. The IOP can fetch and execute its own instructions. These IOP instructions are designed to manage I/O transfers only.

Block Diagram of I/O Processor

Below is a block diagram of a computer along with various I/O Processors. The memory unit occupies the central position and can communicate with each processor.

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Computer Organization Notes Unit -5 The CPU processes the data required for solving the computational tasks. The IOP provides a path for transfer of data between peripherals and memory. The CPU assigns the task of initiating the I/O program.

The communication between the IOP and the devices is similar to the program control method of transfer. And the communication with the memory is similar to the direct memory access method.

Serial Communication

Serial communication is the most widely used approach to transfer information between data processing equipment and peripherals. In general, communication means interchange of information between individuals through written documents, verbal words, audio and video lessons.

In serial communication, data is in the form of binary pulses. In other words, we can say

Binary One represents logic HIGH or 5 Volts, and zero represents a logic LOW or 0 Volts. Serial communication can take many forms depending on the type of transmission mode and data transfer. The transmission modes are classified as Simplex, Half Duplex, and Full Duplex. There will be a source (also known as a sender) and destination (also called a receiver) for each transmission mode.

Synchronous and Asynchronous Transmission

Synchronous Transmission: In Synchronous

Transmission, data is sent in form of blocks or frames. This transmission is the full duplex type. Between sender and receiver the synchronization is compulsory. In Synchronous transmission, there is no gap present between data. It is more efficient and more reliable than asynchronous transmission to transfer the large amount of data.

Asynchronous Transmission: In

Asynchronous Transmission, data is sent in form of byte or character. This transmission is the half duplex type transmission. In this transmission start bits and stop bits are added with data. It does not require synchronization.

Synchronous and Asynchronous Transmission

Point of Comparison	Synchronous Transmission
Asynchronous Transmission
DefinitionTransmits data in the form of chunks or frames	Transmits 1 byte or character at a time
Speed of Transmission Quick	Slow
Cost-effective
Time Interval Constant	Random
Gaps between the data? Does not exist ExistExamplesChat Rooms, Telephonic Conversations, Video ConferencingEmail, Forums,Letters

Standard I/0 interfaces –

Types of Standard I/0 intrfaces

PCI BUS

USB BUS

SCSI BUS

PERIPHERAL BUS):-

INTERCONNECTION

BUS

(PCI

A controller connected to SCSI bus is one of two types – an

initiator or a target.

An initiator has the ability to select a particular target and to send commands specifying the operations to be performed.

The disk controller operates as a target. It carries out the commands it receives from the initiator. The initiator establishes a logical connection with the intended target.Once the connection as been established, it can be suspended and restored as needed to transfer commands and bursts of data.

PCI bus is a system bus.

It supports the functions found on a processor bus but in a standard format that is independent of any particular processor.

Device connected to PCI bus appears to the processor as if they are directly connected to the processor.

PCI bus is very low cost.

UNIVERSAL SERIAL BUS (USB):-

It was developed by several communication companies like Compaq, Hewlett Packard, Intel Microsoft etc.

The USB supports 2 speeds of connection:-

-> Low speed (1.5 megabits/ second)

->Full speed (12 megabits/ second)

The USB is designed to meet Several key objectives:

SMALL COMPUTER SYSTEM INTERFACE

BUS(SCSI BUS):-

It refers to a standard bus defined by the ANSI under the designation X3.131[2]