3.3 COMPUTER SYSTEMS

orangesvetElectronics - Devices

Nov 8, 2013 (4 years and 5 days ago)

82 views

3.3 COMPUTER SYSTEMS

Cristian Hill

3.3.1 Define Operating System


A collection of programs which deal directly
with the hardware system and sub
-
systems,
provide user interfaces and log the activates
taking place in the system.


Examples: Linux, MacOS, Windows, Novell
Netware

3.3.2 Operating System Functions

Peripheral Communication


Peripheral Devices are all hardware outside the
CPU


Only deals with data coded into binary machine
code (See section 3.5.9 for exception)


The OS keeps track of the device drivers and
signals if they are not working correctly


Drivers are software designed to interface directly with the hardware


The OS provides a standard interface between
hardware devices and applications.


The App can the us a <print> type instruction
with in the high
-
level language rather than low
level commands

Coordinating Concurrent
Processing


Concurrent processes are processes or jobs
running on the system the entire time the
computer is on


The OS handles the loading and unloading of
these processes to and from primary memory




Note: “The curious user can get a list of these processes


although it won’t always mean much to the
un
-
initiated” p. 161

Memory Management


The OS ensures that each process runs in its
own (virtual) memory space


It also ensures that each memory space does
not change memory belonging to another
process…in theory

Resource Monitoring


Running processes are allocated resources by OS


E.g. Processor time and memory needed


This is an attempt to keep all processes
running


“It doesn’t always work, you may have noticed”
p.161

Accounting and Security


Multi
-
user, networked, OS’s have to make
sure that only registered users can get access


A manager controls this via OS functions


Logs kept of the activities of the users my be
huge buy necessary if security or other
problems arise


By following the audit trail kept by the
accounting software you can discover
activities of unauthorized users

Program and Data Management


This includes some of the functions already
described


The files, ports and other data resources a
particular programs is using to read and write
information must be kept by the OS


If not one program may write another one’s files


Data transfer and/or program instructions
from files to the primary memory is handled
by the OS

3.3.3 Characteristics of

Computer Systems and a

Comparison of These and

Applications of Different

Computers

Computer Systems


Made of input, processing and output
-
communication hardware devices


As well as the software required to operate and
connect these devices so they can function


May be small and only a single computer (PC) or
of large numbers of computers linked together in
a network


May also vary in size of secondary storage and
memory, processor speed and OS loaded


PC generally allow for ‘multi
-
tasking’

Cont’d

Input Devices
-
mouse,

keyboard, scanner

Processor Unit


processor,

primary memory

and control unit

Output Devices


printer,

modem

Secondary Storage


Hard

drive

System Software


OS

Application software
-

accounting package


Input
devices

Processor
Unit

Output
Devices

Secondary
Storage

Stored

Loaded

System
Software

Application
Software

Data

Personal and Portable
Computers


PC’s are also called microcomputer


Typically has a CD or DVD drive, keyboard,
mouse and monitor, and other wrong
information


Laptops are similar to PC but can run off of
batteries for 2
-
6 hours


Typical cost range: $2,000
-

$10,000


I/O devices are connected via serial and
parallel ports

Note: The book says that USB is a recent development…it came out in 1996, book was
published in 2004.

Mainframe Computers


Designed to run a range of application software
and process large volumes of transactions for
many users at once


Not uncommon for a mainframe computer to
have thousands of users at once


Considerable more amount of RAM and cache


Contains multiple processors and are often run in
parallel


Uses a high capacity disk configuration (aka disk
farm)


Can store TB of data

Cont’d


Cost range in millions of dollars


Traditionally physically large and need own
rooms with expensive air cooling systems


Super Computers


Runs very complex tasks that require large
amounts of processor time


The US Weather Bureau super computer’s
primary memory ( RAM and ROM) is 4 GB in
size

Multi and Single Users
Computer Systems


PC = single user


Multi
-
User computers need to be able to
handle a large number of users logged on
simultaneously


Users are connected via dumb terminal or PC


Dumb terminals do not do any processing

Comparison


Single User System


Multi User System

Single User

CPU

Single CPU which shares
time between users and
other processes

User 1

User 2

User 3

User 4

User 5

User 6

3.3.4 Comparison and Different
Applications of Computer Systems

Instructions


Keep in mind these characteristics:


Primary store size (RAM), backing store size
(online disk and tape capacity), I/O device range,
physical size and cost, type of operation, and
processor word length and speed

Personal and Portable
Computers


Designed to support individuals at home or
work


Typically allows user to create, store, retrieve
and print word processed documents,
connect to Internet, and access to email


Are powerful and can perform complex
financial calculations and graphical
applications

Mainframe


Much more costly than PC


Handles a number of simultaneous users


RAM, cache and disk size are greater


Used primarily by banks, government
departments and insurance agencies


Focused on handling enormous volume of
transactions

Super Computer


Even more expensive than the mainframe or
PC


Faster processor speed


Often uses 100s of PC’s in parallel


Large amounts of RAM and cache


Used to run single computer models such as a
model to predict weather

3.3.5 Computer System Operation
Modes


“Computer systems operation is controlled by
the operating system and the desired mode
of operation” (166)


Other examples of operation modes


Real Time Processing


Interactive On
-
line


Batch Processing

Real Time


Embedded into equipment and have the
basic characteristics of larger Systems


Are pre
-
programmed to act on inputs without
need to alert operator


Thus time between input and action is
reduced


VCR’s and heart monitoring use these
systems

Go VCR’s, thou shalt never die

Interactive On
-
line


Very common


Used in most databases


Operator interacts with the program by
connecting directly to it


Batch Processing


With this there is a time gap between data
collection and data processing


Used to perform a set of processing steps on
a set of data that has been collected over
time

3.3.6 Applications of Different
Modes of Operation

General comparisons


Real time is usually found in embedded chip
technology


The major issue is that they are required to
operate without human intervention


Online systems operate where it is important
that the user has access to the functions of
the System


Batch processing is used where all processing
takes place at once


3.3.7 Relationship Between
Master File and Transaction File


Relationships



The master file contains the main data for a
computer system or application


The transaction file holds a list of changed
needed to be made to the master


These changes are called transactions


In batch processing the data in the master file
may not be up to date

Master File

Update Master

Transaction
File

New Master

3.3.8 Reliability of Systems

Integrity


The correctness of the data is described as its
integrity


The more complex and autonomous the
more mistakes


Multiple systems may be ran in parallel where
failure may be catastrophic

Threats to Data


Unauthorized users may gain access and alter
or remove data


Physical media may be stolen (discs, tapes,
etc. )


Hardware and backups may be stolen


Fire or flood damage

Lions and tigers and bears, Oh my

Protection


Passwords and privileges can be used to
prevent data from being altered


Passwords must be of reasonable length and
hard to guess


Usually 6 or more characters


“not your partner’s, child’s, dog’s, parakeet’s
name” p. 169


When data is transmitted over a network it
may be encrypted if especially sensitive


Cont’d


Encrypting data helps ensure that if it is
accessed it is not readable


A PIN number on the magnetic strip of a bank
card is encrypted for this reason

Backup Strategies


Backup copies are kept in a safe place, usually
in a different building


Backup copies are user to restore a system to
the state existing at the last backup.