Comp Sci HL

abstract data structure

A way of organizing data and its related procedures and functions.

accessor methods

Methods that do not alter the state or attributes of an object; their purpose is to return information.

accumulator

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

A-D converter

Analog-digital converter. A device for converting analog signals into digital ones for subsequent computer processing; sometimes called a "digitizer". A digital to analog (D to A) converter operates in the reverse direction.

ADSL (Asymmetrical Digital Subscriber Line)

Technology that increases the data rate over existing telephone lines accommodating voice and digital data transfer. A special modem is needed for access.

address bus

Pathway from memory to processing unit that carries the address in memory to and from which data is transferred. See the definitions for "bus" and "data bus".

algorithm

An ordered set of well-defined instructions for the solution of a problem in a finite number of steps.

ALU

See the definition for "arithmetic and logic unit".

analog data

The representation and measurement of the performance or behaviour of a system by continuously variable physical entities such as currents, voltages and so on. See also the definition for "digital data".

and

The output of "and" is True if all statements are True, False if any statement is False.

applet (Java)

A program that runs in the context of a browser.

application (Java)

A program that runs when translated by a Java compiler.

archive

Data that represents a record of data held and processed at a specific time, which is held off-line for future research or for legal reasons.

argument

A value or object passed to a method when it is called.

arithmetic and logic unit (ALU)

A part of the computer that performs arithmetic operations, logic operations and related operations.

array

1. An arrangement of data in one or more dimensions.

2. In programming languages, an aggregate that consists of data objects, with identical attributes, each of which may be uniquely referenced by indexing.

ASCII: American Standard Code for Information Interchange

The primary encoding character set used in computers for textual data transfer between applications. The set uses eight bits for each character code, one of these bits being a check bit to verify the seven bits needed to represent one character. ASCII supports most European alphabets. Unicode supports most known alphabets and is increasingly used in data transfer. See also the definition for "Unicode".

attribute

Element of data contained in an object; as specified within the object's class.

B

Byte.

back-up (file)

A second copy of a file, to be used in the event of the original file being corrupted.

balanced tree

A tree in which the right and left subtrees of any node have heights differing by one at the most. See also the definition for "unbalanced tree".

bar code

A pattern of vertical lines distinguished from each other by width. It can be read by a bar code reader to provide data to a computer.

bar code reader

An optical reader that can read bar codes.

base

The basis of a notation or number system, defining a number representational system by positional representation. In a decimal system the base is 10, in a hexadecimal system the base is 16, and in a binary system the base is 2.

batch processing

A method of processing data in which transactions are collected and prepared for input to the computer for processing as a single unit, for example, payroll.

behaviour

The way in which an object reacts to the methods applied

BigO notation

A notation used to describe the relative performance (speed) of an algorithm.

binary operator

An operator that combines two operands to give a single result, for example, addition, multiplication, division, mod, div. See also the definition for "unary operator".

binary search

A search in which, at each step of the search, the set of data elements is divided by two, until the searched element is found. See also the definition for "sequential search".

binary tree

A tree in which each node has at most two children.

bit (b)

Binary digit. The smallest unit of information for data storage and transmission. Each bit is considered to be either a "0" or a "1".

block

The smallest unit of data that can be transferred between memory and backing store in one operation.

BMP

An extension given to files in bitmap form.

Boolean expression

An expression that has a value of True (T) or False (F).

bps

Bits per second.

browser

Generally used to give interactive access to information on the World Wide Web, retrieving web pages and displaying in a multi-media format.

bubble sort

A sort in which the first two items to be sorted are examined and exchanged if necessary to place them in the specified order; the second item is then compared with the third (exchanging them if required), the third is compared with the fourth, and the process is repeated until all pairs have been examined and all items are in the proper sequence. See also the definitions for "insertion sort", "selection sort" and "quicksort".

buffer

A portion of storage used to hold input or output data temporarily.

bus

The pathway used for sending signals between internal components of a computer. Components can share the same bus but cannot transmit simultaneously. See also definitions of "data bus" and "address bus".

bus topology

A network in which all devices are connected to a common cable, known as the "bus". See also definitions of "star topology" and "tree topology".

Byte (B)

A set of bits considered as a unit; it normally consists of 8 bits and corresponds to a single character of information.

cable

Wire or glass fibre used to connect computers over a network. Copper (coaxial and twisted pair) and glass fibre (fibre optic cable) are the most common.

cache

Part of the main store that is between main memory and the processor. It holds a copy of data and instructions that are likely to be used next by the processor and is hence faster than main memory. See also the definition for "disk cache".

CASE

See the definition for "computer-assisted software engineering".

character set

A finite set of different characters that is complete for a given purpose, for example, the 128 ASCII characters.

check digit

A digit added to numerical data that can be recalculated and hence used to check data integrity after input, transmission and so on.

check sum

A sum generated using individual digits of a number and employed as an error-detecting device.

circular queue

A queue in which the storage area is fixed and the first item is held in a location that is logically next to the storage location for the last item of the queue. Data items can be thought of as being arranged in a circle.

clash (collision)

A situation in which two or more entries in a file or other data structure are given the same memory location through the use of a hash table.

class

Combination of data and operations that can be performed on that data; specification of the data members and methods of the object.

client

Desktop computer or terminal used to access a computer-based system.

client-server

A network architecture in which a system is divided between server tasks performed on the instructions received from clients, requesting information.

collection

A class designed to hold objects (referred to in the syllabus as data structure).

command language

A set of procedural operators with a related syntax, used to indicate the functions to be performed by an operating system.

compiler

program that translates a source program into machine code that can be converted into an executable program (an object program). See also the definition for "interpreter".

computer-assisted software engineering

The automation of well-defined methodologies that are used in the development and maintenance of products. These methodologies apply to nearly every process or activity of a product development cycle, for example: project planning, product designing, coding and testing.

computer architecture

The logical structure and functional characteristics of a computer, including the interrelationships among its hardware and software components.

computer program

A sequence of instructions suitable for processing by a computer.

constructor method

A method with the same name as the class that initializes the instance variables of an object of the class when the object is instantiated.

CRC cards

Class, responsibility, collaboration cards. A design tool for classes that lists a class's name, its responsibilities and the classes with which it collaborates on an index card.

cylinder

Concentric disk tracks of a hard disk (one on top of the other) form a cylinder.

database management system (DBMS)

A computer-based system for defining, creating, manipulating, controlling, managing and using databases.

data bus

The pathway between the memory or peripheral and processing unit that carries data for processing or data that has been processed. See also definitions for "bus" and "address bus".

data compression

A method of reducing the size of data. All redundancy in the data is removed to reduce the storage needed or to speed up transfer. The data can be uncompressed back to its original state.

data integrity

The correctness of data after processing, storage or transmission.

data member

A data type that is a member of a class.

data packet

Part of a transmitted message that is sent separately. Apart from containing a portion of the message it will have other data such as check digits, destination address and so on.

data protection

Method of ensuring that personal data is correct and is not misused either by those holding it or others who have no right to access it.

data security

Method of ensuring that data is correct, safe and cannot be read or changed by those who have no right to access it.

DBMS

See the definition for "database management system".

debugging tool

A program used to detect, trace and eliminate errors in computer programs or other software.

defragmentation software

An application that reads file segments from non-contiguous sections of a storage device and then writes the files to the same device in such a way that each file segment is contiguous.

De Morgan's law

If A and B are Boolean expressions, then

A+B=A.B

A.B=A+B

dequeue

To remove an item from the front of a queue. See also the definition

for "enqueue".

digital data

Discrete data.

digital signature

A digital code attached to an electronic message or document, which is unique and which can be used to authenticate the sender or owner. Most often used in electronic commerce.

direct access file

A file organized in such a way that a calculation provides the address (location) of a record so that the record can be accessed directly. The records in the file may be ordered or unordered.

DMA

Access to memory and devices without the direct control of the processor. This is most often used for hard disk access and screen display.

disk cache

RAM set aside to speed up access to a hard drive. This may be part of the disk itself or may be incorporated in cache memory.

distributed processing

A network in which some or all of the processing, storage and control functions, in addition to input/output functions, are dispersed among its nodes.

double buffering

Two areas of memory set aside for data transfer between the processor and peripherals. As one is emptied the other is filled up in order to speed up transfer.

doubly linked list

A linked list in which each node has both a head pointer and a tail pointer.

dynamic data structure

Data structures that can change in size during program execution. See also the definition for "static data structures".

encapsulation

The combination of data and the operations that act on the data to form a single program unit called an "object".

encryption

In computer security, the process of transforming data into an unintelligible form in such a way that the original data cannot be easily obtained except by using a decryption process.

enqueue

To add an item to the rear of a queue. See also the definition for "dequeue".

exception

An object that is created when an abnormal situation arises in a program. See also the definition for "exception handler".

exception handler

A program code that handles exceptions that arise during the running of a program. An exception is thrown to the handler rather than causing a fatal error. See also the definition for "exception".

expression

A sequence of symbols that can be evaluated.

fibre optic

Cabling used for networking that uses fine strands of glass. The medium can carry a great deal of data and it gives a fast transfer rate.

field (object attribute)

A subdivision of a record containing a unit of information. For example, a payroll record might have the following fields: clock number, gross pay, deductions and net pay.

FIFO

First-in-first-out. See also the definitions for "queue", "stack" and "LIFO".

file

An organized collection of data.

file manager

An application software that can access, create, modify, store and retrieve files.

fixed-length records

Records whose size is determined in advance. All such records in a file have the same length. See also the definition for "variable-length records".

fixed point

The performing of arithmetical calculations without regard to the position of the radix point. The relative position of the point has to be controlled during calculations.