F451 Computing notes

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AS Computing F451 Revision Notes
REVISION NOTES FOR MODULE F451 - COMPONENTS OF A
COMPUTER SYSTEM AND MODES OF USE
This document provides you with a series of definitions based on past mark schemes. Every point in each definition
has appeared in at least one mark scheme in the past. You are advised to use these descriptions in your answers,
since mark schemes have a habit of reusing definitions of terms in the marking of questions.
CONTENTS
Components of a Computer System
Software and Operating Systems
User Interfaces
Types of Software
File Organisation
Networking
Error Checking Techniques
Network Transmission
Layered Protocol
Contents of the Protocol
Number systems
Term 2 Revision Notes
Software Development
Systems Life Cycle
Stages:
The Waterfall model of the Systems Lifecycle
Reasons for Developing a New System
Systems Analysis
Fact Finding methods:
Feasibility Study
Diagrams
Design
Tasks completed during the design phase:
Coding/Programming
Testing
Implementation
Changeover Techniques
Maintenance
System evaluation
Documentation
Technical manual ­ describes how the system works. Aimed at technical staff that may need to alter the
system in the future. For example allows debugging of programs assists future developments/upgrades, used
to modify existing file/data structures, supports staff during maintenance of system.
Validation Checks
Application Software
Off-The Shelf Software
Custom Written Software
CAD ­ Computer Aided Design.
Output Formats
Speech Recognition
Image Capture
Information Systems
Management Information System (MIS) -
Expert system -
Inference Engine
Knowledge Base
Robots:
Social, Moral and Environmental
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AS Computing F451 Revision Notes
Tele-work (AKA tele-working).
Legislation
General principles:
Computer Misuse Act
Copyright, Designs and Patents Act
Data Protection Act:
Health and Safety At Work Act
Display Screen Equipment Regulations
Social and Moral
Changes in Work Patterns
Situations caused by the introduction of a new system:
F451 Revision Notes.…read more

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AS Computing F451 Revision Notes
COMPONENTS OF A COMPUTER SYSTEM
Hardware ­ the physical components that make up a computer system.
Software ­ programs and data (groups of instructions to the CPU) used to make the hardware work/produce useful
results.
System software - Systems software controls the hardware/makes the system useable by the operator.
Peripheral (device) ­ hardware device that is external to the CPU. Examples: keyboard, mouse, VDU, etc.…read more

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AS Computing F451 Revision Notes
Hard disk - stores files/software/operating system.
Floppy disk - stores backups of important files to transfer work between machines.
CD-ROM and DVD-ROM - used to import software, store encyclopaedia /databases /video /music /films /backup
files. Always include the suffix when talking about optical disks
CD-RW and DVD-RW ­writeable CD/DVD media, allow backup and transport of data
DO NOT CONFUSE HARD-DISK and MEMORY,
THEY ARE NOT THE SAME THING.
DO NOT USE THESE WORDS INTERCHANGEABLY.
CD-ROM - Compact Disk, read-only.…read more

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AS Computing F451 Revision Notes
Data transfer using buffers (e.g. from primary memory to secondary storage) - data sent to buffer from primary
memory. Interrupt sent when buffer is full, buffer is then emptied to storage device, at slower speed, to
accommodate device. CPU continues on other work. When buffer is empty, interrupt is sent to processor to
request buffer refill. When priority of interrupt is highest of queued interrupts, more data will be loaded into the
buffer.…read more

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AS Computing F451 Revision Notes
SOFTWARE AND OPERATING SYSTEMS
Software - when answering questions on software, do not refer to brand names or trademarks. You should use
generic names (given in descriptions below: word processor, spreadsheet, operating system, etc) and not use words
like Windows, Word, Excel, PowerPoint, Photoshop, Coral Draw
Operating system ­ the suite of programs that controls the operation of the computer, provides an environment in
which applications programs can be run, and provides the user interface to the computer hardware.…read more

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AS Computing F451 Revision Notes
GUI - a graphical user interface. WIMP - uses windows, icons to represent available programs and programs, menus
and pointers. Advantages: easy to use, icons show representation of options.
Menu interface - presents the user with a range of choices, choices may provide a range of further choices in a tree
like manner. Users select choices by pointing to an option. Menus may use function keys, or pointers. May require
many choices to be selected to complete a single command.…read more

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AS Computing F451 Revision Notes
Barcode - patterns of light/dark lines, pairs of which store digits. Barcodes used to store ID code/used to
access record on file. Different widths/pairs of widths used. Inclusion of check digit for automatic checking.
Start and stop codes allow bars to be read both ways.
Stock control data entry: Database has entry for each ID number . When scanned. ID is found in database.
Number in stock field is incremented if goods coming in to warehouse.…read more

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AS Computing F451 Revision Notes
FILE ORGANISATION
Fixed length records - all records are the same length, regardless of the data stored. Limit on the amount of data that
can be stored.
Key field - a field within a record which uniquely identifies a record (e.g. student_admission_number is unique to
each student)
Serial file - records are stored in order of receipt, they are stored in no logical order.
Sequential file - records are stored in order of receipt, or in a logical order.…read more

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AS Computing F451 Revision Notes
NETWORKING
NETWORKING
Network - linking two or more computers (or peripheral devices) to allow them to communicate.
Advantages of networking - network manager has control over network, can monitor use of resources. Shared
physical resources (e.g. hardware), software and files. Allows communications across the network (e.g.
email/Internet access). Users can access via any machine. Maintenance of system more centralised/simpler
backups and loading of software simpler.…read more

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