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A level Computer Science Key
Terms (OCR - H446) – actual
solution
ALU - ANS-Arithmetic Logic Unit "The part of the CPU where data is processed and manipulated. This processing and manipulation normally consists of arithmetic operations or logical comparisons allowing a program to make decisions." CU - ANS-"The part of the CPU that manages the execution of instructions. The control unit fetches each instruction in sequence, and decodes and synchronises it before executing it by sending control signals to other parts of the computer." Register - ANS-"Tiny areas of extremely fast memory located in the CPU normally designed for a specific purpose, where data or control information is stored temporarily." PC - ANS-Program Counter "A register in the control unit which holds the address of the next instruction to be executed."
ACC - ANS-Accumulator A special register within the ALU. It is used to hold the data currently being processed by the central processor. Any data to be processed is stored temporarily in the accumulator, the results ending up back in the accumulator being stored in the memory unit." MAR - ANS-Memory Address Register "A register in the CPU that stores the address of the memory location currently in use. In the fetch phase, this would be the address of the instruction being loaded; in the execute phase, it would be the address of the data being used." MDR - ANS-Memory Data Register "A register in the CPU that stores data being transferred to and from the immediate-access store. It acts as a buffer, allowing the central processor and memory unit to act independently without being affected by minor differences in operation. A data item will be copied to the MDR ready for use at the next clock pulse, when it can either be used by the central processor or be stored in main memory." CIR - ANS-Current Instruction Register "A register in the control unit that stores the address of the next instruction currently being executed and decoded." Buses - ANS-"A common physical pathway shared by signals to and from several components of a computer."
access, so sections of a program and its associated data are copied there to take advantage of its short fetch cycle." Pipelinning - ANS-"The concurrent decoding of two or more machine instructions. While part of one instruction (for example, an address field) is being decoded, another part of a second instructions (for example, an operation code) may also be decoded." Von Neumann Architecture - ANS-"Traditional computer architecture that forms the basis of most digital computer systems. A single control unit manages program control flow following a linear sequence of "fetch-decode-execute"" Harvard Architecture - ANS-"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." Contemporary Architecture - ANS-"Any modern set of disciplines that describes the functionality, the organisation and the implementation of computer systems." CISC - ANS-Complex Instruction Set Computing "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."
RISC - ANS-Reduced Instruction Set Computing "A design that produces a simple, cheap integrated circuit with a basic range of machine instructions. Relies on speed as complex instructions take many machine cycles." GPU - ANS-Graphical Processing Unit "A specialised electronic circuit designed to rapidly manipulate and alter memory to accelerate the creation of images in a frame buffer intended for output to a display. Modern GPUs highly parallel structure makes them more effective than general- purpose CPUs for algorithms where processing of large blocks of data is done in parallel." Multicore System - ANS-"Development of CISC architecture with several sets of CPU components in one microprocessor." Parallel Processor System - ANS-"The simultaneous use of several processors to perform a single job. A job may be split into a number of tasks each of which may be processed by any available processor." Input Device - ANS-"Any peripheral device that can accept data, presented in the appropriate machine-readable form, decode it and transmit it as electrical pulses to the CPU" Output Device - ANS-"Any peripheral device that translates signals from the computer into a human-readable form or into a form suitable for reprocessing by the computer at a later stage."
Virtual Storage - ANS-"A means of apparently extending main storage by using backing storage (such as a hard disk) as if it were main memory." Operating System - ANS-"Collection of systems software that manages the computer. Usually supplied with the computer. Most common operating systems are Windows, Linux, Unix, MacOS, iOS." Memory Managment - ANS-"The process of organising the flexible use of the computer's main memory." Paging - ANS-"The organisation of memory into fixed-sized units, called pages. The immediate-access store is organised as a number of physical pages. The logical pages used by the SPU can be assigned by the memory management unit to any page in physical memory." Segmentation - ANS-"The splitting of a large program unto a number of smaller programs or segments. Each segment is a complete program that is executed separately. The function of the large program is achieved by running segments consecutively. Segmentation allows a large program to be executed on a computer with insufficient memory to store the whole program by carving up memory logically rather than physically." Virtual Memory - ANS-"Used when sufficient immediate-access store is not available. Part of a disk drive is allocated to be used
as if it were main memory. This is very slow, and the software will attempt to use the immediate-access store if possible." Interrupt - ANS-"A signal generated by a source such as an input or output device or a systems software routine that causes a break in the execution of the current routine. Control passes to another routine in such a way that the original routine can be resumed after the interrupt." ISR - ANS-Interrupt Service Routine "A software routine that hardware invokes in response to an interrupt. ISRs examine an interrupt and determine how to handle it." Scheduling - ANS-"The method by which central processor time is allocated in a multi-access system." RR - ANS-Round Robin "A scheduling algorithm that deals with each user or tasks to be processed in turn." FCFS - ANS-First Come First Serve "A scheduling algorithm that deals with each user or task in the order in which they arrive, this can be thought of as a queue." MLFQ - ANS-Multi-Level Feedback Queue "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
Multi-User OS - ANS-"Any operating system designed to allow multiple users to log in and connect to it from different locations / machines at the same time. Specially designed for the sharing of resources such as files, programs or hardware (printers, scanners etc)." Real-Time OS - ANS-"An operating system intended to serve real- time application process data as it comes in, typically without buffering delays." BIOS - ANS-Basic Input / Output System "Part of the operating system that handles the input and output of the computer. It enables the operating system to use the particular features of the hardware being used." Device Drivers - ANS-"A computer program that operates or controls a particular type of device that is attached to a computer." Virtual Machine - ANS-"An emulator of a particular computer system. Virtual machines operated based on the computer architecture and functions of a real or hypothetical computer, and their implementations may involve specialised hardware, software, or a combination of both." Intermediate Code - ANS-"Half-way type of code which is standard across machine types. Runs on a virtual machine."
Application - ANS-"Any program, routine or procedures (together with their associated documentation) that can be run on a computer system." Utilities - ANS-"A systems program that performs some specific task in the operation of the computer, for example file backup, virus checking or a compression program." Open Source - ANS-"Software for which the original source code is made freely available and may be redistributed and modified. - Open source file types are often able to be opened on many different types of applications." Closed Source (Propriety) - ANS-"Often called Proprietary is a type of computer program for which the software code is not shared with the public for anyone to look at or make changes to - Closed / Proprietary file types are often only able to be opened if you own a version of the software they were originally made in." Source Code - ANS-"Original code typed in by the programmer in the native language. This is the code as it appears before it is compiled or interrupted." Translator - ANS-"A program that translates a program written in assembly language into machine code." Interpreter - ANS-"Translates and executes a program one statement at a time."
Linker - ANS-"Software tool that allows already compiled object code files or modules to be combined with the compiled program." Loaders - ANS-A program that copies an object program held on backing store into main store ready for execution." Libraries - ANS-"A collection of pre-compiled routines which can be incorporated into a program." SDLC - ANS-Systems Development Life Cycle "The various stages in designing and implementing a new computer system. These stages - typically analysis, design, implementation, testing and installation - are part of the systems life cycle performed by the main design team. Not be to confused with the Software Development Cycle which is part of the implementation stage of the systems life cycle." Waterfall Model - ANS-"An earlier abstract description of the system lifecycle where each identified stage of development flows from the previous one and down to the next one. Feedback from each to the previous takes place independently of the forward flow." Agile Methodologies - ANS-"Describes the responsive development of a system made of small software modules (often web-based applications) by a group of collaborators who work concurrently and closely under a leader who ensures engineering best practice and delivery of the customer requirements."
Extreme Programming - ANS-"A software development methodology which is intended to improve software quality and responsiveness to changing customer requirements. It is a form of agile development, and as such advocated frequent releases in short development cycles, which is intended to improve productivity and introduce checkpoints at which new customer requirements can be adopted. Other common elements of XP include: programming in pairs or doing extensive code review, flat management structures and avoiding programming of features until they are actually needed." Spiral Model - ANS-"An abstract description of the systems life cycle where there are four defined quadrants - planning, risk analysis, use of design methods, client and management evaluation. Once one stage of development has gone full circle, the next please takes place, and so on until completion." RAD - ANS-"A design strategy that includes online development and repeated prototyping and repeated prototyping and evaluation. It is particularly suited to interactive systems." Programming Paradigm - ANS-"The word 'paradigm' means to describe an example or pattern. In a Computing context, this means to describe a computational way of doing things. So a Programming Paradigm is a style or way of programming. E.g. Low-Level languages, High-Level languages, Declarative languages are all examples of different programming paradigms." Procedural Language - ANS-"Any high level language in which program statements can be grouped in self-contained blocks
register, before the address is used. Index registers are quickly and easily altered providing an efficient way of accessing a range of memory l9ocations, such as in an array." Direct Addressing - ANS-"Uses the data in the address field without alteration. This is the simplest method of addressing and also the most common." Indrirect Addressing - ANS-"Uses the address field to hold the address of a location that contains the required address. Indexed Addressing - ANS-"Modifies the address (either a direct or an indirect address) in the address field by the addition of a number held in a special-purpose registers, called an index register, before the address is used. Index registers are quickly and easily altered providing an efficient way of accessing a range of memory locations, such as in an array." OO - ANS-Object Orientation "Looking at systems by classifying them into real world objects" OOP - ANS-Object Orientated Programming "A method of programming which classifies real world objects into classes and encapsulates those objects attributes and behaviours." Class - ANS-"A type definition of an object" Object - ANS-"An instance of a class."
Base Class - ANS-"Base class contains attributes and methods. It is the highest class and does not inherit from any other class." Super Class - ANS-"A class that has been extended by another class. It allows the extending class to inherit its attributes and methods." Subclass - ANS-"A class that extends another class. The subclass inherits the methods and attributes of the class it extends." Derived Class - ANS-"A derived class is any class that inherits attributes and methods from any other derived class or base class." Insantitation - ANS-"The process of creating an actual named instance of class. The instantiated named copy of the class in an object of that class." Overriding - ANS-"A method in a subclass or derived class which has the same name as a method in one or more of its superclass's. The method supersedes all other versions of the method above it in the inheritance tree." Method - ANS-"A program routine contained within an object designed to perform a particular task on the data within the object. A method can broadly be thought of as a procedure / function from more traditional procedural programming languages."
Symmetric Encryption - ANS-"The oldest and best-known encryption technique. A secret key, which can be a number, a word, or just a string of random letters, is applied to the text of a message to change the content in a particular way. This might be as simple as shifting each letter by a number of places in the alphabet." Asymmetric Encryption - ANS-"This method of encryption involves using a pair of keys to encrypt and decrypt a message so that it arrives securely. Initially, a network user receives a public and private key pair from a certificate authority." Hashing - ANS-"The process of calculating a numeric value from one or more data items. While this value obviously depends on the value of the data items, it need not depend on the meaning attached to them, simply producing a number that is used within the computer." Relational Database - ANS-"Allows the user to specify information about multiple tables and the relationship between those tables" Flat File - ANS-"A database that allows the user to specify data attributes (columns, databases etc.) for only one table at a time, storing those attributes independently" Primary Key - ANS-"A field that uniquely identifies a record in a table" Foreign Key - ANS-"The linking field in the foreign table formed when a relationship is made. The FK becomes by default the PK of the new table."
Concatenated Primary Key - ANS-"When more than one field is added together to form a unique primary key for a table." Secondary Key - ANS-"A key field which can be used to access a table in a different way" ERM - ANS-Entity Relationship Modelling "The process of producing a data model for describing the data or information aspects of a business domain or its process requirements, in an abstract way that lends itself to ultimately being implemented in a data such as a relation database." Normalisation - ANS-"The process of arranging data in tables and setting their relationships to move them through normal forms" Indexing - ANS-"The process of creating a database index, which is a data structure that improves the speed of data retrieval operations on a dataset table at the cost of additional writes and storage space to maintain the index data structure." 0NF - ANS-Zero Normal Form "A table with no normalisation. All data and all fields in one table. A flat file." 1NF - ANS-1st Normal Form "A relationship with repeating groups removed. That is a relation in which the intersection of each tuple and attribute contains one and only one value."
