F451 Computing Fundamentals
Essential Revision Notes
Hardware
An input device is hardware that is used to put data into a computer.
An output device is hardware is display information from a computer
A storage device stores data that has been collected for future use
Hardware is the physical parts of a computer system
A secondary storage device is a peripheral that allows storage of data over a long period of time.
A peripheral is an external device attached to the computer e.g. a printer.
An example of secondary storage would be…
 Hard drive to store the operating system and software to use on the computer,
 CD-RW to backup and transport data
 Memory stick to transport data.
An actuator is anything that gives a physical output such as a pump or a motor.
A sensor is an input device that detects physical quantities e.g. heat/light. Used as part of data logging.
Software
Software is programs and instructions to make hardware do something. Software is written in a language the
computer understands.
Systems software controls the operation of the hardware, runs the computer
An OS is a set of programs designed to manage the hardware of the system
Applications software allows the computer do something useful, e.g. a spreadsheet.
Bespoke software is custom made for a client to perform a specific task.
Utility Software
Compression software
 Reduces size of files. If sending files across internet/email means they are sent more quickly.
Decompressed using a decompression algorithm at the destination
File handlers
 Manages data storage/organises data storage. Allows files to be accessed/deleted/sorted
Hardware drivers
 Contain the instructions to the OS for using a peripheral e.g. Printer has driver to install
communication protocols into the OS. Written in low level language – assembler. Has to
access hardware directly.
Purpose of Operating Systems
 Used to control the hardware of the system/resource management through software like hardware
drivers
 Used to provide a platform on which applications can run. Deals with issues that the software may
have eg storage of files
 Provides a user interface with operator to allow communication between user & hardware
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Handles communications using protocols to govern the communication between components and
peripherals
Provide utility programs used to carry out housekeeping on system e.g. file handlers
Types of Operating Systems
Batch Processing
• Often run during night time/weekends
• No need for human to be present
• Run in computer downtime when workers have gone home
• No need for instant response to inputs
• Processes large amounts of data in one go
• Processing cheques/bills/pay rolls
• Large amounts of similar data that required similar processing
Real Time Processing
• Data is processed instantly
• System responds instantly to changes in input
• Automatic Pilots on airplanes
• Seat booking system – ensures 2 seats aren’t booked simultaneously
Single User
 A single user OS allows one user at a time to use the system. It allocates each user with rights and
keeps the user files separate
Multi User
 Allows more than 1 user to use the system simultaneously – e.g. a network operating system
Multi Tasking
Allows more than one task to run (apparently) simultaneously. Each task is given an amount of
processor time before going on to next task e.g. plays music while typing essay.
Transfer Data from Primary Memory to Secondary Storage
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Data is sent from primary memory to buffer
Processor can continue other tasks
Interrupt sent when buffer is full
Buffer contents emptied to storage device
Data error checked on arrival
When buffer is empty
Interrupt is sent to processor to request buffer refill with data
Interrupt priority compared with priority of present task
Use of priority to assign interrupt with position in queue
Input/Output Devices
Supermarket Checkout
Input devices
 Barcode scanner/reader to input product ID number printed on barcode
 Keypad to input PIN number for card
 Touch screen to allow user to use menu based interface
Output devices
 Screen to show details of objects scanned/current state of transaction
 Printer to print till receipt
 Beeper to indicate valid reading of code
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A barcode is a method of storing data through a series of lines of different thickness. The thickness of each
line represents a number which is scanned by a laser. A check digit is included in the barcode as a method of
error checking. A start and stop digit allows for barcode to be scanned and read both ways.
In a supermarket when a barcode is scanned on a product at the till, this number is searched for on a
database. This is an existence check. The stock level is then decremented to allow for instant stock control
information of each product. If number in stock is less than minimum stock and no order is outstanding for
this item then supplier file is searched for details of supplier which are used and order field is set to show
outstanding order.
MICR is where special characters on document written using magnetisable ink which are both computer and
human readable. Commonly used for printing account numbers on used on banking cheques.
Optical Character Recognition - Characters shapes are scanned and these shapes are turned into text e.g.
scanning a printed page of text into a word processor document.
Optical Mark Reader – Scanned page which reads the positions of marks on a document that are made in a
specific place which denotes inputted data. Multiple choice tests or lottery tickets. Fast and accurate to
process. Useful on multiple choice tests as answers are all objective – no area for debate. Can be processed in
batches.
Automatic Data Capture
 Barcodes
 OMR
 OCR
 MICR
 Image Capture
 Sensors
 Data Logging Systems
o Weather Stations
Advantages of automatic data entry
 Human being does not need to spend time inputting data
 Data input will be more accurate
 No errors to be made
 Data is more likely to be accurately inputed
Expert Systems
Software that is designed to solve problems and provide solution to tasks, such as diagnosis of medical
conditions or analyse large amounts of data.
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Rule Base
Contains all the rules that can be applied to the knowledge/data.
Inference Engine
Uses the rules in the rule base and searches through the knowledge base
Human Computer Interface
Allows for data or queries to be input/results to be output. Common use of a natural
language interface - very complex systems therefore simplification of use is essential.
Processor Components
Control Unit
 Controls fetch/execute cycle. Manages execution of instructions by using control signals to other
parts of computer. Synchronises actions (using inbuilt clock).
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Memory Unit
 Stores the OS/data currently in use and software currently in use
Arithmetic and Logical Unit
 Carries out arithmetic instructions. Carries out logical instructions. Acts as a gateway to processor.
Buses – Channel of communication to send data
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Data Bus
Transmit data between areas of the processor
Address Bus
Identification about where the data is being sent/coming from
Control Bus
Send control signals from control unit to other parts of the processor
Registers – Locations in memory used for specific purposes
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Memory Data Register
o stores the data being transferred to or from memory
Memory Address Register
o stores the address in memory currently being accessed
Current Instruction Register
o stores the instruction currently being executed
Accumulator
o Stores results of calculations performed
Program Counter
o Stores the address of the next instruction and controls the sequence in which the instructions
are executed.
ROM is Read Only Memory and is non-volatile. The contents are not erased when powered off. The ROM
contains the start up program which allows a device to boot up the OS. The start up program is needed
immediately when the device is powered on. The contents of ROM cannot be changed.
RAM is Random Access Memory is a volatile. Contents are lost when powered off. It contains applications
software being used and data used in the operating system. Changes to RAM are made as the device is being
used, and access to RAM is very fast.
A character set is where each character available to input into system is given a unique binary code. On a
standard PC each character on the keyboard has a 1 byte ASCII code. Other character sets are UNICODE
which uses 2 bytes. The more characters required the more bits in each code.
Data Transmission
Serial is one bit transmitted at a time down a single wire. Parallel is multiple bits transmitted at a time down
many wires.
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Simplex
o Communication in one direction only
Half Duplex
o Communication in both directions but one at a time
Duplex
o Communication in both directions simultaneously
Bit rate is the rate at which data is transferred, how many bits in a specific time period. Measured in bits per
second also known as baud rate.
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A fast internet connection is required to steam a video. A video has a large volume of data which needs to be
transmitted at a very fast rate. A video is time sensitive unlike other data such as a text files which contain a
relatively small amount of data.
Protocol
A protocol is a set of rules that governs communication between devices.
To establish communication between 2 devices a handshake signal sent from one device and and
acknowledged by the other. This states that each is now ready for communication. Agree logical parts of
protocol such as the error detection and baud rate that will be used to transmit data
The physical part of the protocol can be if data is transmitted wireless or hard-wired, Serial or parallel or the
type of cabling used e.g. copper wire, or fibre optic, what frequency will be used in a wireless network.
If different frequencies are used then the receiving device will never receive the communication as it will be
listening to different parts of the frequency
The logical part of the protocol is things that are programmed in software such as baud rate the error
correction used, and any compression techniques used. Needed as if one device transmits data at a different
rate than it is received the bits in the data will be mixed up.
Networks
A local area network is a network covering a single building or site. A WAN covers a wide geographical
area crossing countries and continents. LAN is more secure than a WAN.
To establish a network physical items required are a NIC, cabling and a server. A network operating system
and hardware drivers for the NIC are also needed.
To connect to the internet a router or modem is required. A router connects a LAN to a WAN. A modem
converts digital signals to analogue signals to communicate down a phone line.
A handshake is an exchange of signals between devices to signify that they are ready for communication.
Protocols will be agreed prior to the communication beginning. Without agreement on rules the two devices
cannot understand each other’s signals.
Packet Switching
Data split into packets sent onto network. Each packet finds the fastest route to destination. Packets must be
reordered at destination/arrives in wrong order. Packets have identity on label
No established route for each packet – doesn’t tie up parts of network.
Data cannot be easily intercepted
Maximises use of network
Only as fast as its slowest packet!
Circuit Switching
Route reserved before transmission. Establishes a route along which to send data. Data sent down this route
in its entirety. Can ties up large areas of network
Error Detection
Echoing
Once data is received it is sent back to destination and compared to see if it is the same. Verification.
Check Sum
Blocks of bytes are added before transmission to give a sum. The sum is transmitted with the block. The
same calculation is done on the data blocks at the destination and result is compared with the transmitted
value. If different, there is a transmission error
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Parity
The total number of 1’s in a byte must add up to either an odd or even number depending on the parity bit.
The parity bit is set to either a 1 or 0 to check the byte has been transmitted correctly.
Validation Methods
Validation ensures data meets certain rules. These are programmed in the software.
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Range Check
o A number between 1 and 10 e.g. >=1 and <=10
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Character Check
o Only allowing letters to be used in a name field
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Format Check
o A field may required letters and numbers in a certain order e.g. NI number is 2 letters, 6
numbers, 1 letter.
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Length Check
o Only allowing a minimum or maximum number of characters in a field e.g. mobile phone
number can’t be more than 11 digits.
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Existence Check
o Barcode is read at supermarket till. That number is looked up on a database. If number is not
on database then it must have been incorrectly inputted.
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Presence Check
o Data has been entered into a field.
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Check Digit
o An algorithm is performed on a string of numbers or characters to give a digit. This digit is
transmitted along with the string. The same algorithm is performed to ensure the check digit
is the same when received. Used on barcodes, ISBN (mod 11).
System Life Cycle
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Feasibility study
o Technical
o Economic
o Social
Analysis
Design
Implementation
Testing
Evaluation
Maintenance
o Corrective
o Adaptive
o Perfective
Spiral
Developer works through each stage of the system lifecycle over and over again, and each stage is refined
each time to produce the final system.
Waterfall
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Developer finishes each stage of the system life cycle in order and moves onto the next stage once each stage
is fully completed.
Developer uses RAD to develop the front end of the software. Produces series of prototypes with heavy
involvement from end user to ensure product meets their demands.
When conducting a feasibility study 3 factors have to be considered…
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Technical
Can hardware/software be found to implement the solution
Economic
Is the proposed solution possible within budget/economic to run
Social
Effect on the people/employees involved – jobs, retraining, new skills needed
Methods of Fact Finding
Need to ensure analyst understands the organisation requirements or system produced may not meet
requirements
 Interview
One to one situation/can change course of questions/Boss or client
 Questionnaire
Have their views considered/time saving/large workforce
 Observation
See process in action/may not act as they would because being observed
 Meeting
Get views from many people at once/may be taken over by one or two people
 Document collection
Indicates what data is actually collected.
Requirements Specification
 Input requirements
 Output requirements
 Processing requirements
 Clients agreement to requirements
Design Specification
 Input design
 Output design/choice of interface
 System flow charts
 Data flow diagrams
 Entity Relationship Diagrams
Installation Planning
When installing a new system there a 4 methods of doing so.
 Parallel
Run both systems side by side until the new one is considered error free. Used in situations where
data is valuable so can't afford mistakes
 Pilot
Try new system in one small area of business/company. See how it works before rolling out new
system to whole business.
 Big Bang
Old system removed and new one starts immediately
 Phasing
Parts of old system replaced gradually.
Evaluating the new system
 End User Requirements decided on in analysis. Does new system meet them?
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Important to user because need to be sure software performs as required – is it actually what they
wanted. Important to developer because it determines the end of the job if they are being paid for
producing a suitable solution
Future Enhancements
Three types of maintenance are…
 Corrective
To correct bugs found in software when being used
 Adaptive
To alter software because of external need eg VAT increase
 Perfective
To improve performance of software
User Documentation
 How to operate the system
 Error messages/trouble shooting
 FAQ
 Required hardware specifications
 Software install procedure
 Backing up and archiving procedure
 Glossary
 Index
 All written from users point of view
Technical Documentation
 Data Flow Diagram
Flow of data through system
 System flow chart
How parts of system interrelate
 Entity Relationship Diagram
How data tables relate to each other
 Variable Names, Data Structure, how the code works
 Meant for future programmers
Data Security
Methods to keep data secure are
 Passwords that restrict access to system to certain users. Passwords can be made more secure –
alphanumeric, minimum length, change every set period of time.
 Use of a firewall to stop signals from unauthorised users reaching the system/hardware or software
 Encryption so that if unauthorised access is gained the data is unintelligible
 Proxy server restricts the users allowed access to individual machines on network
Types of User Interface
A GUI is a graphical user interface which uses WIMP. A GUI is very processor intensive.
A CLI is a command line interface. The user has to type in specific commands to operate the system. The
user needs to be computer literate to use it as they have to remember all the commands and their syntax. CLI
requires very little processing power.
A menu based interface is a list of on screen choices which leads to further menus which allows the user to
choose an action from a set list of options. These are commonly used on a touch screen information terminal
or a mobile phone. A menu based interface is easy and intuitive to use and requires little training or computer
literacy. A GUI is more difficult to use and more processor intensive.
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A natural language interface is where the user communicates with the computer in a human conversation
type way. Used with some internet search engines and expert systems. Requires no training or computer
literacy. Very difficult to program due to the ambiguous nature of human language.
When designing a user interface factors to consider are…
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Form of output
o Sound may be inappropriate/inaccurate on a noisy factory floor
Volume of data
o User must not be subjected to information overload as this may lead to omissions
Colours
o Needs to be readable/sensible use of colours like red for danger
Experience of user
o CLI not suitable for inexperienced user
Layout
o Spread around screen, font size
Hardware platform
o Suitability for the application/environment to be used in. GUI very processor intensive.
Forms of Output
Different types of output could be…
 Reports / text / printouts
 Sound
o to act as an alarm (in case of emergency action being required).
 Video / visual display / images
o showing real-time actions/images
 Diagrammatic
 Flashing/Highlighted Text
o highlights important information.
 Graphical /Charts
 Flashing Light
o to act as an alarm to show problem with an area of the track.
Backup and Archiving
A backup is a copy of a file and its structure on a portable medium kept away from originals so that if the
original is corrupted it can be replaced. Important files needs be protected from deliberate or accidental data
loss.
Archiving is where data is put onto long term storage and kept offline so that it can be referred to if
necessary. Data is still available without taking up space on working storage.
A backup routine needs to consists of the following aspects…
 How often backup is done
 Time of day it is performed
 Medium of storage used to store the backup
 Where the backup is stored
 Full or Incremental Backup
 Generations of backup – Grandfather, Father, Son
Implications of Computer Use
Some people are concerned about their data being stored electronically because concerns their personal
details could be hacked by outsiders, become victims of identity theft, personal data can be sold on to
companies for marketing purposes. Errors in their personal data leading to problems/miscalculations.
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Measures to be taken to overcome peoples concerns are
 Check accuracy of the data being stored
 Allow people to view the data that is stored about them
 Limit access to small number of security screened people
 Abide by data protection legislation
 Ensure data is secure – firewalls, passwords, secure servers, encryption
 Physical security of data – restrict access to employees,
Data protection Act governs the storage of personal data electronically. It is required because
 Information is confidential and sensitive
 Information must be accurate
 Clients must have confidence that measures are taken to protect their data
 Ensure irrelevant data is not kept
 Concerns about identity theft/fraud
 Stops data being passed onto 3rd parties for marketing purposes.
Effects of Home Working
Advantages
 Less pollution from travelling
 Less traffic congestion
 Less infrastructure required
 Greater opportunities for employment of disabled people
 Do not need to supply offices/car parking spaces
 Cheaper to run offices
 Work can be outsourced easily
 Employees have more freedom with family
 Save money/time on commuting
Disadvantages
 Lack of social contact
 Less structure in society
 Difficulty if system goes down
 Communication with work colleagues more difficult
 Less control over work of individuals
 More difficulty in altering course of work
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