computer science

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Accumulator

A storage register in the ALU that holds data temporarily while the data is processed and before it is transferred to memory.

Address Bus

Carries the address of an instruction or data. From the CPU to the memory unit

ALU (Arithmetic Logic Unit)

The part of the CPU that perform basic arithmetic and logic operations (add, subtract, multiply and divide).

Bus

Communication lines that transfer data between components inside a computer

Cache

Memory inside the processor providing fast access to frequently used instructions and data.

Clock speed

The speed/frequency at which the internal clock generates pulses. Measured in Hertz and is generated by a crystal or oscillator located somewhere on the motherboard.

Control bus

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

Control unit

Decodes instructions. Sends signals to control how data moves around the CPU

Core

A processing unit within a CPU

CPU (Central Processing Unit)

The key component of a computer system, which contains the circuitry necessary to decode and execute a program

Current Instruction Register (CIR)

Register that stores the instructions that the CPU is currently decoding/executing

Data Bus

Used by the CPU to send and receive data.

Fetch-Decode-Execute Cycle

The process of retrieving an instruction from memory, decoding it and carrying it out

Harvard architecture

Instructions and data stored in separate memory units

Each memory unit has its own bus

Reading and writing data can be done at the same time as fetching an instruction.

Memory Address Register (MAR)

Holds the address in memory of the instruction at present being executed. Located in the CPU

Memory Data Register (MDR)

a register that contains the data value being fetched or stored.

Pipelining

A technology that allows a processor to begin executing an instruction before completing the previous instruction.

Program Counter (PC)

The register that contains the address of the next instruction to be executed

Register

Tiny areas of fast memory located in the CPU

Designed for a specific purpose, where data or control information is stored temporarily

Von Neumann Architecture

A processor where data and instructions are stored in the same memory and accessed via buses.

Merge sort

A divide and conquer algorithm. A list is repeatedly divided into smaller lists eventually containing just one item. Each element is compared with the adjacent list and merged back together from two lists into one

Linear search

Examining each data item in turn until the item is found or the end of the data structure/file is reached.

Dijkstra's shortest path

A graph search algorithm that finds the shortest path between two nodes.

Bubble sort

Moving through a list repeatedly, swapping elements that are in the wrong order.

Big O notation

A way of expressing the worst-case run-time of an algorithm, useful for comparing the speed of two algorithms.

Algorithm

A sequence of steps designed to perform a particular task.

A* algorithm

An algorithm that finds the shortest path between two nodes. Widely used in pathfinding and graph traversal. It keeps a sorted priority queue of alternate path segments along the way.

Visualisation

The process of turning data into a visual representation which is easier for humans to understand, interrupt and work with.

Problem recognition

The acknowledgement and definition of an issue that may arise during the performance of a process.

Problem decomposition

The process of breaking a complex problem or system into parts that are easier to conceive, understand, program, and maintain.

Performance modelling

This is the process of carrying out mathematical approximations of how well a system will perform.

Heuristics

Mental shortcuts or "rules of thumb" that often lead to an approximate solution (but not always).

Selection

A decision point within a computer program.

Procedure

A routine within a larger program that can take parameters that is used to produce structured code. Does not return a value.

Passing by value

A copy of the data is used, which is discarded after the procedure or function has been completed.

Passing by reference

The address of the data is used. This means that any changes are retained after the procedure or function has been completed.

Parameter passing

The process of providing a procedure, function or module with values at the point when you call it.

Parameter

Data structures passed into a procedure/function/subroutine when they are initially called.

Modularity

A technique of code design where a solution is broken down into a number of subroutines.

Local variable

A variable which is defined and can only be used within one part of the program.

Iteration

Code which is repeated a set number of times, or a variable number of times based on the evaluation of a Boolean expression.

IDE (Integrated Development Environment)

A programming tool that gives programmers a single environment (that is, the hardware and software environment in which the program runs) for building programs rather than using individual editors and debuggers.

Global variable

A variable that can be used in any part of the program.

Function

A section of code that may take parameters that can be called by another part of the program with the purpose of returning a value.

Debugging

The process of removing syntax, logical and run-time errors from computer code.

System outputs

Anything which exits a system in any form in order for it to operate as intended.

System inputs

Anything which will be required to go into a system in any form in order for it to operate as intended.

Solution preconditions

Any condition which must exist for the solution to work.

Concurrent processing

More than one operation happening at the same time.

Recursion

A function that calls itself.

Sequence

Instructions executing one after another.

Data mining

The analysis of a large amount of data to provide new information.

Backtracking

An algorithm that finds all (or some) solutions to computational problems by returning to a previously successful result to find an alternative solution. It abandons each partial success as soon as it determines that the partial solution cannot possibly be completed.

Binary search

A search algorithm that starts at the middle of a sorted set of numbers and removes half of the data; this process repeats until the desired value is found or all elements have been eliminated.

Insertion sort

Each items is taken in turn, compared to the items in a sorted list and placed in the correct position within the list.

Quick sort

A divide and conquer algorithm. Selecting a 'pivot' element from the list and partitioning the other elements into two sub-list according to whether they are less than or greater than the pivot.

Abstraction

Including only the necessary details and leaving out the unnecessary details when problem solving.

Abstract model

A simplification of a real system.

RIPA (The Regulation of Investigatory Powers Act)

Legislation which regulates the powers of public bodies to carry out surveillance and investigation, and covering interception of communications.

DPA (Data Protection Act)

Legislation which protects individuals from unreasonable use of their store personal data.

Copyright Designs and Patents Act

Legislation which gives creators of works the right to control the ways in which their material may be used.

CMA (Computer Misuse Act)

Legislation which makes it illegal to make unauthorised access to data; with the intent to commit further offences or modify data.

Truth table

The output of a logic gate/circuit for all possible combinations of inputs.

Logic gate diagram

A method of showing Boolean logic in a diagram using a set of symbols called logic gates

Karnaugh map

Method of simplifying a complex boolean calculation.

Half adder

A unit which adds together two input variables. A half adder can only add the inputs together and not a carry bit

Full adder

A unit which adds together two input variables and can also add a carry bit from another addition

D-type flip flop

A basic circuit that can storage one bit and flip it between values. It can only be in two stable states - representing 1 and 0.

Double negation

A rule or law in Boolean algebra where if you invert a term twice it is equal to its original term: NOT NOT A \= A

Distribution

A rule or law in Boolean algebra that permits the multiplying or factoring out of an expression.

De Morgan's law

Two laws in Boolean algebra:

1. AND and OR, or union and intersections, are dual

2. NOT (A and B) is the same as (NOT A) or (NOT B)

Commutation

A rule or law in Boolean algebra stating that the order of application of two separate terms is not important.

Boolean logic

A form of mathematics in which an expression is reduced to either True or False.

Boolean algebra

A set of rules for manipulating truth values according to truth tables.

Association

A rule or law in Boolean algebra that permits the removal of brackets from an expression and regrouping of the variables.

Undirected graph

A graph that contains edges between vertices with no specific direction associated with any edge.

Tuple

Another name for a database record. An immutable data structure.

Tree

A non-linear dynamic data structure where data items can be thought of as occurring at different levels. There are links (pointers) between items at one level and their descendants at the next.

Stack

A dynamic data structure, where the last item in is the first out.

Record

A data structure which consists of a elements of different data types. A collection of related data items for one entity.

Queue

A dynamic first in first out data structure.

Linked list

A list where each item contains the data together with a pointer to the next item.

Hash table

A table of information that is accessed by way of a shortened search key (the hash value). An implementation of a dictionary for key-value pairs.

Directed graph

A graph in which the order of the vertices in the pairs in the edge set matters.

Binary search tree

A data structure where each node can have only 0, 1 or 2 leaf nodes. All left nodes and all of its descendants have smaller values that the root node. All right nodes and all of its descendants have larger values than the root node.

Array

A set of data items of the same type grouped together using a single identifier, where each of the data items is addressed by the variable name and a subscript. A static data structure.

XOR (Exclusive OR)

An operation that outputs to true only if one input is true and the other input is false.

Unicode

A character code that enables most of the languages of the world to be symbolized with a special character identification.

Two's complement

Storing positive and negative numbers where the most significant bit (MSB) is a negative value and not a sign.

String

A sequence of characters often stored as a variable in a computer program. These characters can include numbers, letters and symbols.

Sign and magnitude

A method of storing positive and negative numbers in binary. The most significant bit (MSB) is a 0 for a positive number and a 1 for a negative number

Shift

An operation that moves the bits held in a register, called the shift register, either to the left or the right.

Real

A data type used to store numbers with a fractional part.

Primitive data type

The basic data types provided by a programming language.

OR

OR works by returning TRUE as long as either value being compared is TRUE.