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GCSE Computing revision:
A451 Written exam.
Computer systems | Hardware | Software | Data representation | Databases | Networks & The Internet | Programming
Revision resources.
Includes everything you
need to know for the
written exam.
http://www.cambridgegcsecomputing.org/new-course
http://www.bbc.co.uk/education/subjects/z34k7ty
http://www.teach-ict.com/gcse_computing/ocr/GCSE_A451_topics.html
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A451 GCSE Computing | Hardware| Required knowledge
Hardware
Binary logic
-
-
Why do computers use binary values?
Logic gates
-
Truth tables
-
Definition.
Components
Input
Process
Storage
Output
Computer architecture
Von Neumann
Central processing unit (CPU)
-
-
Arithmetic & logic unit
Control unit.
Fetch-execute cycle
Fetch
De-code
Execute
The boot sequence
Clock speed
Processor speeds (MHz, GHz)
Cache memory
Multiple processor cores
Advantages / disadvantages.
Memory
-
Random Access Memory (RAM)
Volatile
Read Only Memory (ROM)
Non-volatile
Virtual memory
Flash memory
Input devices
- Keyboard
- Mouse
- Touch screen
- Microphone
- Camera
- Sensor
- Bar code scanner
- Eye-typer
- Foot mouse
- Puff-suck switch
- Braille keyboard
Output devices
- Monitor
- Printer
- Plotter
- Speakers
- Actuators
Secondary storage
- Magnetic hard disk
- Optical disk
- Flash memory
- Considerations for selecting
storage:
- Capacity
- Speed
- Portability
- Durability
- Reliability
John Von Neumann
It is your responsibility to make sure you regularly revisit this knowledge outside of class.
Hardware keywords
Keyword
Definition
CPU
Central processing unit - processes program instructions. Also called a
microprocessor.
Fetch-execute cycle
Process by which a computer processes instructions.
Clock speed
The speed of a computer CPU, measured in hertz. The number of times a second a
computer carries out the fetch-execute cycle.
Core
A processing unit within a CPU. CPUs can have multiple cores.
Storage
The hardware of a computer that stores data long term, such as a memory card or
hard drive.
Memory
The part of a computer that stores data.
Cache memory
A piece of temporary memory. It can refer to a part of the RAM, storage disk, CPU, or
an area for storing web pages.
RAM
Memory that is constantly being written to and read from. It does not retain its
contents without a constant supply of power, ie when a computer is turned off,
everything stored in its RAM is lost.
Volatile memory
It does not retain its contents when the power is switched off.
ROM
Memory or storage that has data stored on it that cannot be changed, i.e.
Non-volatile memory
It does retain its contents when the power is switched off.
Virtual memory
A section of a computer storage drive which is temporarily used as RAM.
Hardware keywords from memory.
Keyword
CPU
Fetch-execute cycle
Clock speed
Number of cores
Storage
Memory
Cache memory
RAM
Volatile memory
ROM
Non-volatile memory
Virtual memory
Definition
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Software keywords
Keyword
Definition
System software
Controls the hardware, e.g. operating system.
Application software
Handles the real world jobs that users want to do, e.g. word processor.
Utility software
Has limited functionality and is used to maintain computers, e.g. Antivirus.
Operating system
Set of programs that controls hardware & lets users and applications work
with the computer.
Defragmentation
Used to tidy up disks by storing parts of files next to each other.
Disk clean-up
Searches for unused files and clears them out.
Virtual memory
When a computer uses secondary storage to temporarily act as RAM.
User interface
Boundary between the human user and machine.
Authentication
Check that users are who they say they are, e.g. username / password.
Privileges
Rights assigned to users and groups, e.g. read / write / read & write.
Open source software
Software placed in the public domain – access to source code.
Custom written software
Software commissioned for a specific purpose.
Proprietary software
Software developed for profit. Source code retained and kept secret.
Off the shelf software
Bought from a shop and ready to install, e.g. MS Office or Windows.
Software keywords from memory
Keyword
System software
Application software
Utility software
Operating system
Defragmentation
Disk clean-up
Virtual memory
User interface
Authentication
Privileges
Open source software
Custom written software
Proprietary software
Off the shelf software
Definition
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A451 GCSE Computing | Data representation| Required knowledge
Numbers
-
Binary – base 2.
Denary – base 10.
Converting from binary to denary.
Converting from denary to binary.
Adding binary numbers.
Overflow error
Units.
Nibble
Byte
Kilobyte
Megabyte
Gigabyte
Terabyte
Hexadecimal (hex) numbers
-
Hex – base 16
Converting between hex and
denary.
Converting between hex and
binary.
Characters
-
Images
-
Stored in binary on a computer.
Metadata
Pixel
Colour depth
Resolution
Bitmap images
Vector images
Sound
-
-
Metadata
Sample rate
Quality of sound
File size
Sample interval
Bit rate
Instructions
-
Fetch-Execute cycle
Op-code
Operand
Accumulator
Character set.
Definition
ASCII
Unicode
It is your responsibility to make sure you regularly revisit this knowledge outside of class.
Data representation keywords
Keyword
Definition
Binary (base 2)
A number system that contains two digits, 1 & 0 (also known as base 2).
Denary (base 10)
The number system most commonly used by people. It contains 10 unique digits 0 to 9.
Also known as decimal or base 10.
Hexadecimal (base 16)
A number system using 16 characters from 0 to 9 and A to F, also known as hexadecimal.
Character set
A complete collection of characters.
ASCII
A 7-bit set of codes that allows 128 different characters. That is enough for every uppercase letter, lower-case letter, digit and punctuation mark on most keyboards.
Unicode
Unicode uses between 8 and 32 bits per character, so it can represent characters from
languages from all around the world. It is commonly used across the internet.
Image resolution (images)
The fineness of detail that can be seen in an image - the higher the resolution of an image,
the more detail it holds. It is measured in dots per inch (dpi).
Colour depth (images)
The colour depth of an image is measured in bits. The number of bits indicates how many
colours are available for each pixel.
Sampling interval (sound)
Time between samples being taken. The higher the sample interval, the lower the sample
rate.
Sampling rate (sound)
How many samples of data are taken per second. This is normally measured in hertz, eg an
audio file usually uses samples of 44.1 kHz (44,100 audio samples per second).
Operand (data)
Data that is manipulated by opcodes in a CPU machine code instruction set.
Op-code (instruction)
Specifies instructions that can executed by a CPU in machine code.
Meta-data
Metadata means 'data about data' and provides information about the image, e.g. file
format, colour depth, resolution, e.t.c.
Data representation keywords from memory
Keyword
Binary (base 2)
Denary (base 10)
Hexadecimal (base 16)
Character set
ASCII
Unicode
Image resolution (images)
Colour depth (images)
Sampling interval (sound)
Sampling rate (sound)
Operand (instructions)
Op-code (instructions)
Meta-data
Definition
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Database keywords
Keyword
Database
Definition
Persistent organised store of data.
Entity
Something in real life about which we store data.
Table
Where data is organised and stored in a database.
Primary key
Uniquely identifies a record.
Foreign key
A reference to a primary key in a relational database table.
Flat file database
A database that stores data in a single table.
Relational database
A database that stores data in multiple tables that are linked
together.
Validation
Process of checking data as it is being input, e.g. length check.
Verification
Checking that data is correct.
DBMS (Database
management system)
Data redundancy
A tool to store, edit and organise a database.
Unnecessary repetition of data.
Database keywords from memory
Keyword
Database
Entity
Table
Primary key
Foreign key
Flat file database
Relational database
Validation
Verification
DBMS (Database
management system)
Data redundancy
Definition
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Long answer question.
@CES_teach
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A451 GCSE Computing | Networks | Required knowledge
Networks
Network technicalities.
The internet.
-
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Collection of connected
computers.
- LAN
- WAN
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Network hardware
-
Network interface card (NIC).
Cables
-
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Unshielded twisted pair (UTP)
Fibre-optic
Hub
Switch
Wireless access point
Router
Types of network
-
Client-server network.
Peer-to-peer network.
Protocols
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TCP/IP
Data packets
Domain Name System (DNS)
File Transfer Protocol (FTP)
Hypertext Transfer Protocol
(HTTP)
-
-
-
-
Network security
-
Backups
Archives
Failover
Disaster recovery
Authentication
Acceptable use policies
Modem
Router
Addressing
-
Packet switching
IP addressing
MAC addressing
Network topologies
Diagram, advantages and
disadvantages of the following:
- Bus
- Ring
- Star
-
The internet vs. World Wide
Web
Hardware
Uniform Resource Locator
(URL)
IP address
Domain name System (DNS)
Hypertext markup language
(HTML).
-
Cascading style sheets (CSS)
Internet file standards.
-
Meaning and uses for each of
the following:
-
-
JPG
GIF
PDF
MP3
MPEG
Compression
- Lossy
- Lossless.
Images via
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It is your responsibility to make sure you regularly revisit this knowledge outside of class.
‘Networks’ keywords
Keyword
Definition
Topology
Arrangement of various elements of a computer network.
Client-server network
Services / applications are hosted on a central server and accessed via client computers.
Peer-to-peer network
All computers on the network have equal status – no central server.
Router
Device for connecting computers together to form a network.
Server
A computer that holds data to be shared with other computers.
Switch
Intelligent device – used to connect computers together. Sends packet of data to requested
computers.
Network Interface card (NIC)
Needed in order for a computer to connect to a network.
MAC address
Media Access Control – each piece of hardware on a network has a unique MAC address.
IP address
Numerical address assigned to each device that connects to the internet.
Domain Name System (DNS)
Internet service that translates domain names into IP addresses.
HTML
Hyper Text Markup Language – used to write and display web page documents.
Protocol
A set of rules for how messages are turned into data packets and sent across a network.
Lossy compression
Reduces the file size by permanently deleting redundant information.
Lossless compression
Every bit of data remains in the file when it is uncompressed.
Networks - keywords from memory.
Keyword
Topology
Client-server network
Peer-to-peer network
Router
Server
Switch
Network Interface card (NIC)
MAC address
IP address
Domain Name Server (DNS)
HTML
Protocol
Lossy compression
Lossless compression
Definition
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A451 GCSE Computing | Programming | Required knowledge
Algorithms.
Control flow
-
-
-
Flowcharts
Symbols
Pseudo-code
Written English.
Use of indentation.
-
Comparison operators
Sequence
Selection
IF… ELSE…
Iteration
For
While
Programming languages.
-
-
Low level languages:
Machine language
Op-code
Operand
Assembly language
Mnemonics
High level languages:
Source code
Assembler
Compiler
Interpreter
Integrated development environment
(IDE).
-
Source code editor.
Error debugger.
Run time environment.
Translator (compiler or interpreter).
Automation tools
Auto-complete code.
Auto-complete documentation
Data types
-
Integer e.g. 23
Real e.g. 23.7
Character e.g. A or 5
String e.g. A546TH
Boolean e.g. TRUE or FALSE.
Comparison
operator
Meaning
= or ==
Is equal to
>
Is greater than
<
Is less than
<> or !=
Is not equal to
>=
Greater than or equal to
<=
Less than or equal to
- Operator priority: BIDMAS
Variables & constants
-
-
Named storage space reserved in
memory.
Both declared.
Definition of variable.
Definition of constant.
Data structures
-
Arrays
Definition
Example
Testing
Operations
-
ADD +
SUBTRACT –
DIVIDE /
MULTIPLY *
MOD
DIV
-
-
Test data should be chosen to
cover valid, invalid, extreme &
erroneous situations.
Logic errors
Definition & examples.
Syntax errors
Definition & examples.
It is your responsibility to make sure you regularly revisit this knowledge outside of class.
Programming keywords
Keyword
Definition
Algorithm
A sequence of logical instructions for carrying out a task. In computing, algorithms are needed to
design computer programs.
High level programming
language
A computer programming language used to write programs. They need to be translated into
machine code through a compiler, interpreter or assembler.
Low level programming
language
Low-level language is a programming language that deals with a computer's hardware components
IDE (Integrated
development environment)
Integrated development environment - a piece of software used to write computer programs.
De-bugging
The process of finding and correcting programming errors.
Sequence
In computer programming, this is a set of actions that follow on one from another.
Selection
A decision within a computer program when the program decides to move on based on the results
of an event.
Iteration
In computer programming, this is a single pass through a set of instructions.
Variable
In a computer program, this is a memory location where values are stored.
Constant
A value in computer programming that does not change.
Compiler
A special program that processes statements written in a particular programming language and
turns them into machine language or "code" that a computer's processor uses.
Interpreter
A computer program that directly executes, i.e. performs, instructions written in a programming or
scripting language, without previously compiling them into a machine language program.
Programming keywords from memory
Keyword
Algorithm
High level programming
language
Low level programming
language
IDE (Integrated
development environment)
De-bugging
Sequence
Selection
Iteration
Variable
Constant
Compiler
Interpreter
Definition
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