A level computer science p1

This review of lecture notes covers fundamental concepts and prepares the student for an upcoming exam.

Numbers written using the symbols 0,1,2,3,4,5,6,7,8,9 for each digit.

Denary numbers

A digit in the binary number system written using either of the symbols 0 and 1.

Bit

A group of eight bits treated as a single unit.

Byte

A group of four bits.

Nibble

A prefix to define the magnitude of a value. Examples are kilo, mega, giga and tera representing factors of 10^3, 10^6, 10^9 and 10^12 respectively.

Decimal prefix

A prefix to define the magnitude of a value. Examples are kibi, mebi, gibi and tebi representing factors of 2^10, 2^20, 2^30 and 2^40 respectively.

Binary prefix

The binary number obtained by subtracting each digit in a binary number from 1

One’s complement

The one’s complement of a binary number, plus 1

Two’s complement

A condition when the result of a calculation is too large to fit into the number of bits defined for storage

Overflow

Storage of a binary value representing one denary digit in a nibble

Binary coded decimal (BCD)

When two BCD nibbles are stored in one byte

Packed BCD

A graphic consisting of drawing objects defined in a drawing list

Vector graphic

A component defined by geometric formulae and associated properties

Drawing object

Contains one set of values for each drawing object

Drawing list

Defines one aspect of the appearance of the drawing object

Property

The smallest identifiable component of a bitmap image, defined by just two properties: its position in the bitmap matrix and its color

Picture element (pixel)

The number of bits used to represent one pixel

Colour depth

The number of bits used to represent each of the red, green and blue colours

Bit depth

The number of pixels in the bitmap file defined as the product of the width and the height values

Image resolution

The product of width and height values for the number of pixels that the screen can display

Screen resolution

A set of bytes at the beginning of a bitmap file which identifies the file and contains information about the coding used

File header

Data obtained by measurement of a physical property which can have any value from a continuous range of values

Analogue data

Data that has been stored as a binary value which can have one of a discrete range of values

Digital data

Taking measurements at regular intervals and storing the value

Sampling

The number of bits used to store each sample

Sampling resolution

The number of samples taken per second

Sampling rate

Coding techniques that allow subsequent decoding to recreate exactly the original file

Lossless compression

Coding techniques that cause some information to be lost so that the exact original file cannot be recovered in subsequent decoding

Lossy compression

A network connecting computers on different sites, possibly thousands of kilometers apart

Wide area network (WAN)

A network connecting computers in a single room, in a single building or on a single site

Local area network (LAN)

An architecture where a client runs an application provided by a server on a network

Client-server

A client that only provides input and receives output from the application

Thin-client

A client that carries out at least some of the processing itself

Thick-client

The configuration of a network that defines how the various devices on the network are connected

Topology

Contains one shared link to which all devices are attached

Bus topology

A computer or server connected to a network

End-system

Contains direct links between devices

Mesh topology

Each end-system is linked to a central device

Star topology

A collection of connected LANs where some of them have different topologies or supporting technologies

Hybrid network

A transmission using copper wire or fibre-optic

Cable

A measure of the amount of data that can be transmitted per second

Bandwidth

A transmission using radio, microwave or infrared

Wireless

A system providing a service to end-systems

Server

A device that connects two cables and provides a full-strength signal to the second cable

Repeater

A device that connects two segments of a LAN

Bridge

A component used to identify the end-system

Network Interface Card (NIC)

A connecting device that can send a unicast message

Switch

The connecting device in a WiFi LAN

Wireless Access Point (WAP)

Provides the NIC function in a WiFi LAN

Wireless Network Interface Card (WNIC)

A device that acts as a node on the Internet

Router

When the bit stream content is transmitted at a time chosen by the user

On-demand

When the bit stream content is transmitted as it is produced

Real-time

The number of bits transmitted per second

Bit rate

A 32-bit long, hierarchical address of a device on the Internet

IPv4 address

A hierarchical distributed database installed on domain name servers that is responsible for mapping a domain name to an IP address. Also known as domain name system.

Domain name service (DNS)

Owned by and only accessed by an organization

Private cloud

Owned by a cloud service provider for general access

Public cloud

Volatile memory that can be read from or written to any number of times

Random-access memory (RAM)

Non-volatile memory that cannot be written to but can be read from any number of times

Read-only memory (ROM)

A temporary storage created for data transmitted from one part of the system to another which functions as a queue

Buffer

Consists of hardware components which the processor can access directly

Immediate Access Store (IAS)

Controls the cycles of activity within the processor

Internal clock

Controls the cycles of activity outside the processor

System Clock

A general-purpose register that stores a value before and after the execution of an instruction by the ALU

Accumulator

A component that carries an address. This can be to the memory controller to identify a location in memory which is to be read from or written to or it can be to the I/O system to identify the source or destination of the data

address bus

The component that can carry data from the processor to the memory or to an output device or can carry data from the memory or from an input device

data bus

A small number of bytes that can be handled as a unit by the computer system

Word

A screen back-lit by light-emitting diodes and with liquid crystal cells sandwiched between polarisers

Liquid-crystal display (LCD)

A flexible surface that causes contact between electrically resistive layers beneath when touched

Resistive touch screen

A rigid surface above a conductive layer that undergoes a change in electrical state when a finger touches the screen

Capacitive touch screen

The point in a computer program where processing stops in order for data to be inspected

Breakpoint

A component of a logic circuit that has an operation matching that of a Boolean operator

Logic gate

A statement that is either TRUE or FALSE

Logic proposition

An informal definition of an outcome which is dependent on one logic proposition or a combination of two or more logic propositions

Problem statement

Logic propositions combined using Boolean operators, which may be equated to a defined outcome.

Logic expression

The action defined in the instruction

Opcode

Defines instructions a value to be used

Operand

A binary code with a defined number of bits that comprises an opcode and, most often, one operand

Machine code instruction

A low-level language related to machine code where opcodes are written as mnemonics and there is a character representation for an operand

Assembly language

Software used to translate an assembly language program into machine code

Assembler

Instructions given to the assembler

Directive

Is where the instruction uses a value and defines how the operand must be used to find the value

Addressing mode

Is where bits in the accumulator are shifted to the right or left and a zero moves into the bit position vacated

Logical shift

A file based approach that causes it has to have accurate and up to date data

Data Integrity

File based approach which requires Data to be available only to authorized users

Data Privacy

File based approach that indicates data is secure if available for use and data is that of the original data stored

Data Security

Is a result of malware resulting in intent to cause harm to the system

Malware

A means of establishing a legal user is the actual user logging into a system, by the means of passwords or more complex means

Authentication

Is a way that IT systems help to govern and monitior use of the the system, but may include a need for legal enforcement

Data Protection Law

Is where you code for a program

Source Code

Is that what the complier has created

Object Code

A hardward/software that provides a means to monitor traffice, ensuring only the required access to the users that need it

Firewall

A formal recognition of ownership of a created and plublished work, providing a level of legal ownership

CopyRight

Is one where the bits move, and the most significant bit is moved to carry bit, the rest shifting and having an entry to a bit zero to the LSB.

Cyclical Shift

Also uses the shift to carry out multiplication or division of an signed integer stored in the
accumulator

Arithmetic Shift

A means to create a visual guide to an IT programmer, prettyprinting provides use

PrettyPrinting

Is one that involves an easy way to perform and store information

Utility program

Uses a developer interface to give access to soft ware tools within datadictionary

DBA

A way to create and apply a check to data upon data entry or input

Data Validatation

The requirement of the data by the programmer is tested via the key, the way

Foreign Key