Chapter 6: Computer Input and Output

Topics: Input/output, Input device, Computer Pages: 54 (1921 words) Published: January 21, 2015
CHAPTER 6
Computer Input
and Output

Importance of I/O devices to
MIS
 They

provide the hardware interface
between the manager and the
central processing unit.

 I/O

devices are used by employees in
processing the daily transaction data
of the firm.

I/O Devices in General
System Model
Manager

Information
Processor

I/O Devices in General
System Model
Some of the gathered data is first
recorded on some type of medium,
such as:
 punched cards
 magnetic tape
 magnetic disk.

Offline key driven machines
Convert source data to a computerreadable medium. Other data is originally recorded in a form that is
acceptable to the computer
Ex.
 Magnetic ink character recognition
(MICR)
 Optical character recognition (OCR)
This approach is called SOURCE DATA AUTOMATION


Offline key driven machines
A

third basic way to enter data into
the computer is to key it into an
online key driven device.

A

fourth option permits data input in
audible form, using a voice
recognition unit.

Input Options
Source
data
Key to
tape
Machine

Computer readable data

OCR
docs
MICR
docs
Keyboard
Terminals
MICR, OCR
units

Card,
tape, disk
Units
Channel
s

Voice
Recognitio
n

CPU

Offline key driven machines


Output offers similar options.
Information or data can be recorded
on a permanent medium, such as
paper, microfilm, or punched cards,
or the information can be displayed
on a television like screen or
presented audibly.

OUTPUT options
CPU
Channels

Print
er
informatio
n

Termin
al
Displa
y

Plott
er
informatio
n

Computer
Output
Microfilm
Microfil
m
Microfi
lm
printer
informatio
n

Card
punch
Unit
Punch
Cards
Microfil
m
Viewer

Channels and Control Units
The control unit contains the logic
circuitry and storage needed for the
control of multiple I/O devices. The
channel contains the logic circuitry
and storage needed to monitor
several I/O device control units and
provide pathways to and from the
CPU.

Role of Channels and Control
Units
Channels

Control Units

High Speed
Channel

Control
Unit
Control
Unit

CPU

Low Speed
Channel

Control
Unit
Control
Unit
Control
Unit

I/O Devices

Channels and Control Units


The transfer of data between the I/O unit,
the control unit, and the channel is serial,
or one byte at a time. When this
operation is performed, the CPU can
process other data in primary storage.
The CPU halts processing just long
enough to enter the data from the
channel. The interruption of the program
in process is very brief because all of the
bytes from the channel are transmitted to
primary storage at once—in parallel.

Channels and Control Units


The transfer of data from primary storage
to an I/O unit works in the reverse
sequence.



Smaller computers have only one
channel; larger systems have many.

Channels and Control Units
Importance of the channels:
 Easy to overlook, but without them CPU
performance would be drastically reduced.
 The channel hardware and the operating
system permit the multiprogramming that
maximizes computer productivity.
 Without channels, there could be no time
sharing or distributed processing, and
batch processing would extremely slow
and costly.

KEYDRIVEN INPUT
DEVICES

Offline Keydriven Devices
 The

most common input device was
the keypunch machine.
 The first key-to-tape and key-to-disk
units used conventional magnetic
tape reels and hard disks.

Offline keydriven Machines
Keypunch
Machine

Key to
tape
Machine

Key to
disk
Machine

Punch Cards
Convention
al
magnetic
tape
Tape
Cassette
Hard disk

Floppy disk

Card
Reader
Magnet
ic tape
unit
Casset
te
Magnet
ic disk
Unit
Floppy
dsik
Reader

CPU

Magnetic tape cassette

Contains 285 ft. of polyester.
Data can be recorded at the density of 800 bytes per...
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