3.3 COMPUTER SYSTEMSCristian 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 Applicatio

n 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 portsNote: 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 CPUSingle CPU which

shares time between users and other

processesUser 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.