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HARDWARE I/O ORGANIZATION

Chapter 10I/O Device Management

What is Hardware?

The physical components of computers.

We can touch and see the hardware.

Monitor,Mouse,Keyboard,hard drive etc are the hardware devices.

Stands for Input/output devices

Input:

The instruction given to the computer. A hardware component is used to enter data in computer such as keyboard etc

Output:

A hardware component used to display information to the user such as printer etc

What are I/O Devices?

SINGLE-BUS ARCHITECTURE

It is used by simplest Computers.

Can process one instruction at a time.

all units are connected in the same bus.

Only two devices can communicate with each other at one time.

Protocol is required to control the communication.

Time is broken in to clock cycle.

A special device decides which device will communicate in the next class called Bus Arbitor.

Input Output Memory Processor

Single-Bus Architecture

Advantages or Disadvantages

Advantages or Disadvantages

Advantages

Simplicity

Low cost

Disadvantages

Limited speed

The bus can became a major bottleneck.

Multiple-Buses Architecture

Can Process two instructions at a time.

Parallelism

• multiple communications are possible at the same time with multiple buses.

• For example CPU can communicate with port or disk wants to communicate with memory on another bus.

Performance Tuning

Peripheral Component Interconnect bus is used to connect devices

Special memory bus is used for optimized communication between CPU & memory.

Industry Standard Architecture bus is connected to PCI to provide backward capability for older ISA devices.

I/O Control

In the simple I/O Control Model, CPU communicates with I/O devices Directly.

CPU controls all details of device operation.

This communication used in specialized, Microprocessor-controlled, embedded system.

In pc model, CPU communicates with a device controller.

Each I/O controller is designed to handle a particular kind of device.

I/O channel

I/O control unit

Execute channel programs

Programs loaded in memory or

channels memory

Ports and Memory-Mapped I/O

1)Port I/O

2)memory-mapped I/O

Port I/O

Limited numbers of instructions provide I/O capability in it.

One instruction operands is an I/O port number.

Memory Mapped I/O

Any instruction that access memory can access an I/O module.

A part of memory Space is allocated to I/O modules.

Module Registers

Different modules have different types of numbers and registers.

A simple module for input device may have only two registers ,one for data and one for control information.

The data register stores the value.

Control registers contains bits to command module.

Busy Wait I/O

It is a protocol for communication between I/O modules and CPU.

CPU issues a signal to I/O module to start I/O operation.

It is inefficient because processes can make no headway while CPU waits for the completion of I/O operation.

POLLED I/O

CPU continues to execute different processes in the system after starting operation in it.

Polling is more efficient.

CPU checks for the completion of I/O operation after brief intervals.

The disadvantage is that the processes are interrupted when CPU checks for the completion of I/O operation.

Interrupt I/O

An interrupt can be sent to CPU when I/O operation is completed.

In this way CPU, continues to executes until it gets interrupt from I/O module.

It provides parallelism but adds complexity in the code.

Direct Memory Access (DMA)

• DMA is a technique that is used to send data directly from a device to the memory.

• CPU is not involved in this transformation that results in speeding up the overall computer operation.

• a specified portion of memory is designed for DMA.

• DMA is required when a large amount of data is moved

CPU I/O Memory DMA

CPU issues a command to DMA module when it requires to read or write a block of data .It sends the following information to DMA module1. Types of operation required such as read or write 2. The address I/O device involved3. The starting location in memory to read from or

write to.4. The numbers of words to be written or read .

Working

• The CPU then continues with other work.

• It has delegated I/O operation to the DMA module .

• DMA module will then transfer the entire block of data one word at a time directly to or from memory without going through CPU.

• DMA module sends an interrupt signal to CPU when the transfer is complete.

• CPU is only involved at the beginning and at the end of data transfer.

• DMA works while CPU is idle and is not using the system bus,.

• It is called cycle stealing.

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