Download On-Line & Real-Time Modes of Use Presentation

Operating Systems
Modes of Use / Operation
On-Line & Real-Time
23/05/2017
1
Learning Objectives
Discuss modes of computer use and the
interrelationship between applications and
modes of use.
Describe the characteristics of different
types of operating systems.
Describe the uses of different types of
operating systems.
23/05/2017
2
Operating Systems
(Types of / Modes of operation)
Single-User
Interactive
Network
Time Slicing /
Sharing
Multiprocessing
On-line
Real-time
Multi-tasking
Off-line
Batch
Multi-Access /
User
This presentation focuses
on these modes.
Simple Client-Server
Network System
23/05/2017
Distributed
Network System
3
On-line
User has direct contact with processor
Used when:

Processor needs to be constantly ready to receive
input
Justified by:
Explaining why processor needs to be constantly
ready to receive input.
 Or if real-time is necessary and has been justified then
state:

“On-line as otherwise system cannot be real-time.”
Back
23/05/2017
4
Real-time
•Data processed or action is taken at time of input, quickly
enough to affect the next input.
•Is by definition also on-line.
•Used when a system must react immediately when input
from a sensor or other input device is received as a delay is
unacceptable.
•Used in process control or transaction processing.
•These are the two different types of real-time operating system.
•Justified by:
•Explaining what action must be taken immediately and why a
delay is unacceptable.
Disadvantage
Transaction Processing
Transaction processing systems also attempt to provide
predictable response times to requests, although this is
not as critical as for real-time systems.
Rather than allowing the user to run arbitrary programs
as time-sharing, transaction processing allows only
predefined, structured transactions.
Each transaction is usually short duration and the
processing activity for each transaction is programmed in
advance.
Largely database related.



IGCSE “Databases Quiz” & “Databases - Theory Test”.
http://www.teachict.com/gcse_new/computer%20systems/operating_system_types/mini
web/pg7.htm
http://en.wikipedia.org/wiki/Transaction_processing_system
23/05/2017
6
Process Control
Process control is extensively used in industry and enables mass
production of continuous processes such as oil refining, paper
manufacturing, chemicals, power plants and many other industries.
Process control enables automation, with which a small staff of
operating personnel can operate a complex process from a central
control room.
Process control may either use feedback or it may be open loop.
Control may also be continuous (car cruise control) or cause a
sequence of discreet events, such as a timer on a lawn sprinkler or
thermostat on a heater (on/off) or controls on an elevator (logical
sequence).
Note that sensors DO NOT turn output devices on/off (the CPU does
this based on the readings it receives from sensors), although the
page from Wikipedia below suggests that it does:

See the IGCSE “Processing Quiz” and “Processing Test”.
23/05/2017
http://en.wikipedia.org/wiki/Process_control
7
Disadvantage of Real-time
•Speed mismatch implications:
•The computer will not be using its full
potential as far as processing is concerned.
•Because the computer cannot be using up some
of its slack time doing other tasks while it is
waiting to be asked to do something.
Examples
Real-time Use & Justification 1
Driving a racing car around a track.

Turning the wheel must turn the car
immediately.
Process control
Next
23/05/2017
9
Real-time Use & Justification 2
ATM computer system
Checking of PIN/identification
 Checking of funds available

to ensure person has the right to extract cash, or
long wait is possible
Transaction processing
Next
23/05/2017
10
Real-time Use & Justification 3
A chemical plant has a reaction vessel where the
temperature is critical to the result of the process.

The temperature is monitored by a computer which
accepts input from a sensor and then makes a
decision whether to adjust the heating elements in the
vessel.
If there was a delay in the decision making
process, it might mean that the reaction is
corrupted in some way.
Process control
Next
23/05/2017
11
Real-time Use & Justification 4
A robot trolley is controlled by a processor
which takes input from a sensor following a
black line on the floor, and makes
decisions concerning steering to keep the
trolley on the black line.

The trolley would very soon leave the black
line because it would not be steering quickly
enough.
Process control
23/05/2017
Next
12
Real-time Use & Justification 5
A catalogue shop processes orders by the code for a
product being input and the system then comparing the
code with information in its files.
When it finds the correct code it can report to the user the
number of that item that there are in the store.


If there was only one left of a certain item, it would be necessary
to record the fact that a shopper had bought it before the next
shopper has their request dealt with otherwise the second person
might be sold the same item.
Because the information on the system must be processed
immediately the O.S. needs to be ready to handle input as soon
as it comes in.
Transaction processing
23/05/2017
Back
13
Plenary
Define the terms On-line and Real-time
processing:
23/05/2017
14
Plenary
On-Line
User is able to communicate with processor
directly
Real-Time
 Data processed at time of input / input
processed quickly enough to effect the next
input.

23/05/2017
15