OCR A level computer science definitions

studied byStudied by 11 people
5.0(1)
get a hint
hint

Accumulator

1 / 245

Tags and Description

246 Terms

1

Accumulator

A register in the CPU that stores data currently being used by the CPU.

New cards
2

Address bus

Used to transfer information about where data should reside in memory

New cards
3

Arithmetic Logic Unit

The part of the CPU that performs arithmetic computations and logical operations.

New cards
4

Buses

A physical set of parallel wires connecting and carrying groups of bits between several components of a computer.

New cards
5

Cache

A small and fast but expensive memory in the CPU used to stores instructions and data that are accessed regularly.

New cards
6

Clock speed

The frequency at which the internal clock generates signals switching between 0 and 1. It controls how often instructions are executed and data is fetched.

New cards
7

Contemporary processor architecture

A modern computer architecture combining elements of both Von Neumann and Harvard architectures.

New cards
8

Control Bus

This bus carries command and control signals to and from every other component of a computer.

New cards
9

Control Unit

Component of a processor that directs and coordinates most of the operations in the computer.

New cards
10

Current Instruction Register (CIR)

A register inside the CPU which holds the current instruction (not the data)

New cards
11

Data bus

The bus used to transfer actual data between main memory and the MDR

New cards
12

FDE cycle

Fetching an instruction from memory, decoding what the machine code means, then running the instruction with the result stored in the accumulator

New cards
13

Harvard Architecture

A computer architecture with physically separate storage and signal pathways for instructions and data. These early machines had data storage entirely contained within the central processing unit, and provided no access to the instruction storage as data.

New cards
14

Memory Address Register (MAR)

Holds the address in memory of the instruction currently being executed.

New cards
15

Memory Data Register (MDR)

A register that contains the data value being fetched or stored

New cards
16

Cores

A unit that handles instructions with its own FDE cycle. Multi-core processors have multiple cores that can run simultaneously.

New cards
17

Pipelining

The simultaneous decoding of several instructions by decoding the next instruction and fetching the one after while the current one is being decoded.

New cards
18

Program Counter (PC)

A special purpose register that stores the address of the next instruction to execute.

New cards
19

Registers

Small, high-speed storage locations that temporarily hold data and instructions.

New cards
20

Von Neumann Architecture

A computer architecture with a single control unit, using the FDE cycle and with data and instructions stored together.

New cards
21

Complex Instruction Set Computer (CISC)

A design that produces a complicated and expensive integrated circuit capable of performing a large variety of complex instructions. Complex instructions can be executed with few machine cycles.

New cards
22

Graphics Processing Unit (GPU)

A specialised processor optimized to perform graphics calculations with a huge number of small cores that allows for efficient parallel computation (SIMD).

New cards
23

Multicore systems

Several CPU cores are incorporated into a single processor chip to help distribute workload

New cards
24

Parallel processing system

Splitting a job into several subtasks which are simultaneously carried out by each core in the system.

New cards
25

Reduced Instruction Set Computer (RISC)

A simpler processor design that can only execute a single simple instruction each clock cycle. This uses more RAM but allows pipelining.

New cards
26

Flash Storage

A solid state technology that stores data on a collection of memory chips. No moving parts as data is accessed by software.

New cards
27

Input devices

Peripheral devices that allow the user to communicate and to pass readable data into a computer, decode it and send it to the CPU.

New cards
28

Magnetic storage

Relies on the polarisation of magnetic particles to store bits on a magnetic material which is typically moved mechanically. A high capacity and low cost means of storage.

New cards
29

Optical storage

Data is stored in the reflectivity (pits and lands) of a surface, and is read and written to by a laser.

New cards
30

Output devices

Peripheral devices that convert signals from a computer into a human-readable form.

New cards
31

Random Access Memory

Memory used to store programs and data in use by the computer. Quick access times but all data is lost when power to the computer is lost (volatile)

New cards
32

Read Only Memory

Memory used to store programs or data that is permanently required to boot up and run the computer. Can only be read and is non-volatile

New cards
33

Storage device

Any medium on which data can be stored even when powered off

New cards
34

Virtual storage

Using the hard disk as though it were an extension of memory to free up more RAM for current programs.

New cards
35

BIOS

A program that initialises and tests whether system hardware is functional and then loads the operating system from the hard disk into RAM when the computer is turned on.

New cards
36

Device drivers

A program supplied with a peripheral device that allows the OS to control and communicate with the device.

New cards
37

Distributed Operating System

The operating system is spread over multiple computer servers on a network, acting as a single system to parallel process a job

New cards
38

Embedded Operating System

A specialised operating system with limited resources and functionality, built in to control a single machine.

New cards
39

first come first served (FCFS)

A scheduling algorithms where processes are dealt with in the order they arrive (a queue)

New cards
40

Intermediate code

Code partly translated between high-level and machine language produced by a compiler.

New cards
41

Interrupts

A signal from hardware, software or the clock to alert the CPU. If the interrupt is a higher priority than the current task, the current routine pauses and resumes after the interrupt is executed.

New cards
42

Interrupt Service Routine (ISR)

If an interrupt is of higher priority that the current task, register contents are temporarily transferred onto the system stack at the end of the current FDE cycle and the interrupt is handled.

New cards
43

Memory management

The efficient organisation and allocation of main memory to the programs in use

New cards
44

Multi-Level Feedback Queue (MLFQ)

A complex scheduling algorithm that deals with tasks based on a set of priorities and rules across different league tables, jobs in a certain table get promoted up or down their table based on these rules and can then end up in totally different tables if they relegated.

New cards
45

Multi-tasking operating systems

An operating system capable of running multiple tasks simultaneously

New cards
46

Multi-user operating systems

An operating system consisting of one mainframe computer with multiple terminals that allow multiple users to access the computer's resources. Each user is given a time slice of the mainframe processor

New cards
47

Operating system

A set of programs managing the operating of the computer that is loaded into RAM every time the computer is turned on. It allows the user connection to the hardware.

New cards
48

Paging

Partitioning memory into fixed sized physical divisions called pages. Processes in memory are assigned an appropriate number of pages.

New cards
49

Real-Time Operating System

An operating system where data is processed as it comes in, with responses generated in real time

New cards
50

Round robin

A scheduling algorithms where each process is given an equal time slice and is dealt with on a first in first out basis. If a process doesn't finish in the allotted time then it is moved to the end of the queue

New cards
51

Scheduling

Allocating processor time to each application to ensure processor time is used as efficiently as possible when multitasking

New cards
52

Segmentation

Partitioning memory into variable size, logical divisions called segments. A large programs can be executed by consecutively running its segments

New cards
53

Shortest job first

A scheduling algorithm that picks the process with shortest estimated running time and runs it until it finishes.

New cards
54

Shortest remaining time

A scheduling algorithm that picks the process with shortest estimated time remaining to finish. If a process with a shorter time is added, the scheduler switches processes

New cards
55

Virtual machines

Any instance where software is used to take on the function of a machine, including intermediate code or running an operating system within another

New cards
56

Virtual memory

An allocated area of secondary storage where pages of inactive jobs are swapped in to free up enough RAM for the current job

New cards
57

Applications

A program that can be run on a computer, allowing the user to carry out specific tasks

New cards
58

Assembler

A translator in a low level language which converts assembly language into machine code

New cards
59

Closed source

Proprietary software sold with a license and restrictions on how users can use it. The source code isn't available to users.

New cards
60

Code generation

The third and final of compilation, where an equivalent machine code program is produced

New cards
61

Compilation

The process of analysing high level language source code and converting it into machine code

New cards
62

Compilers

A translator that converts source code into object code that cannot be easily converted back into a human-readable format. The code is translated all at the same time rather than line by line.

New cards
63

Interpreters

A translator which checks a source program for errors line by line, translates it to machine code and executes the file.

New cards
64

Lexical analysis

The first stage of compilation, where extra spaces and comments are removed from the source code and it is searched for simple errors. Keywords, constants and variables are replaced by tokens. Variable names are loaded into the symbol table

New cards
65

Libraries

A collection of pre-compiled routines which can be incorporated into a program.

New cards
66

Linkers

A program which places the appropriate machine addresses in the call and returns instructions of a compiled program so all the other required object code files and modules are linked together

New cards
67

Loaders

A program that loads the executable object program and its associated libraries into memory before it is run.

New cards
68

Open source

Software which has code that is readily available to view, redistribute or modify

New cards
69

Optimisation

During code generation, the object code is made as efficient as possible by removing redundancies to produce code that gives the same result

New cards
70

Syntax analysis

The second stage of compilation, the object code is made as efficient as possible by removing code redundancies (repeated code) to produce code that gives the same result

New cards
71

Translator

A program which converts code from one computer language to another

New cards
72

Utilities

System software with a specific purpose, usually maintenance such as backing up files, diagnosing issues or setting up firewalls

New cards
73

Agile Methodology

An iterative process that aims to improve the flexibility of the programmer and meet the requirements of the end-user. Prototypes are developed in parallel so that it can adapt to changes in user requirements quickly.

New cards
74

Extreme programming

Type of agile methodology intended to improve software quality and responsiveness to changing customer requirements. Programmers work in pairs with the focus being on high quality code.

New cards
75

Rapid Application Development (RAD)

Prototypes developed and evaluated against user requirements until the prototype can become the final product.

New cards
76

Spiral model

An iterative version of the Waterfall model where stages are refined and repeated until the final product is complete. The first cycle works towards an initial prototype, and each successive cycle produces a refined prototype

New cards
77

Waterfall lifecycle

Sequential stages, each stage must be completed for the next to follow, previous stages can be returned to if the full cycle is repeated again.

New cards
78

Assembly language

A low level language closely related to (but more advanced than) machine code. It uses mnemonics for instructions.

New cards
79

Attributes

Data recorded as a variable associated with an object.

New cards
80

Classes

A template defining the attributes and methods that can be used to create an object.

New cards
81

Direct addressing

The operand stores the memory address of the value to be operated on by the operator. (The most simple addressing mode in assembly language).

New cards
82

Encapsulation

A method of maintaining data integrity by only allowing class methods to access data in an object's attributes.

New cards
83

Immediate addressing

An addressing mode in assembly language in which the instruction holds the value of the operand rather than its address.

New cards
84

Indexed addressing

An addressing mode in assembly language where the address of the operand required is calculated by adding a constant from the index register to the absolute address in the instruction.

New cards
85

Indirect addressing

An addressing mode in assembly language where the operand stores the address of the location holding the memory address of the required data.

New cards
86

Inheritance

The concept of subclasses inheriting the methods and attributes of its parent class

New cards
87

Object-oriented language

Programming languages where the code is made of units called objects which are instances of a class. Objects have their own attributes and behaviours and can interact with each other.

New cards
88

Objects

An instance of a class. The behaviour of an object depends on how its attributes were defined.

New cards
89

Polymorphism

Objects of different classes can use the same method to perform an action

New cards
90

Procedural languages

A high level language where statements are grouped into self-contained blocks called functions and procedures. They have built in data types and data structures.

New cards
91

Programming paradigms

A style of computation and programming, chosen according the problem at hand.

New cards
92

Asymmetric encryption

An encryption technique where a public key is used to encrypt the data and a private key is used to decrypt.

New cards
93

Dictionary coding

A type of lossless compression where text is searched for entries that match the entries present in the dictionary. Entries are substituted by a unique code which can then be translated

New cards
94

Hashing

A one-way transformation of data into a hash value. The hash value cannot be returned into the original value.

New cards
95

Lossless compression

A compression algorithm that allows the original full sized file to be decompressed

New cards
96

Lossy compression

A compression algorithm that removes non-essential data from a file leading to a considerable decrease in file size. The original file is unrecoverable.

New cards
97

Run length encoding

A type of lossless compression where repeated occurrences of the same data are stored as a single data value alongside their counts

New cards
98

Symmetric encryption

An encryption technique where the same key is used to both encrypt and decrypt the data.

New cards
99

Atomicity

All transactions must succeed or fail, no inbetween

New cards
100

Consistency

Each transaction must obey the defined validation rules of the database to main referential integrity.

New cards

Explore top notes

note Note
studied byStudied by 4 people
Updated ... ago
5.0 Stars(1)
note Note
studied byStudied by 103 people
Updated ... ago
5.0 Stars(2)
note Note
studied byStudied by 6 people
Updated ... ago
5.0 Stars(1)
note Note
studied byStudied by 7 people
Updated ... ago
5.0 Stars(1)
note Note
studied byStudied by 5 people
Updated ... ago
5.0 Stars(1)
note Note
studied byStudied by 4 people
Updated ... ago
5.0 Stars(1)
note Note
studied byStudied by 17 people
Updated ... ago
5.0 Stars(1)
note Note
studied byStudied by 608 people
Updated ... ago
5.0 Stars(3)

Explore top flashcards

flashcards Flashcard130 terms
studied byStudied by 23 people
Updated ... ago
5.0 Stars(1)
flashcards Flashcard173 terms
studied byStudied by 115 people
Updated ... ago
5.0 Stars(2)
flashcards Flashcard89 terms
studied byStudied by 3 people
Updated ... ago
5.0 Stars(1)
flashcards Flashcard152 terms
studied byStudied by 22 people
Updated ... ago
5.0 Stars(1)
flashcards Flashcard59 terms
studied byStudied by 9 people
Updated ... ago
5.0 Stars(1)
flashcards Flashcard63 terms
studied byStudied by 4 people
Updated ... ago
5.0 Stars(1)
flashcards Flashcard26 terms
studied byStudied by 4 people
Updated ... ago
5.0 Stars(1)
flashcards Flashcard574 terms
studied byStudied by 11255 people
Updated ... ago
4.6 Stars(54)