Computer Science Paper 1 Definitions


Systems Architecture 1

CPU = Fetches, decodes and executes instructions in order to process data.

Von Neumann ArchitectureWhere instructions and data are stored in main memory to be accessed by a microprocessor.

MAR = Memory Address Register contains the address of the location in main memory being accessed.

MDR = Memory Data Register contains the data that has just been read in or is about to be written out to main memory.

PC = Program Counter contains the address of the next instruction to be executed.

Accumulator = A general purpose register often used to hold interim results.

CIR = Current Instruction Register holds the instruction that is currently being executed.

CU = The Control Unit sends signals down the control bus to ensure the correct functioning of the CPU.

ALU = The Arithmetic and Logic Unit is responsible for performing arithmetic or logical tests.

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Systems Architecture 2

Cache = This is very fast storage (bigger than a register) that is physically located on the same chip as the microprocessor.

Processor or Clock Speed  = Measured in Hertz (Hz).

Processor Core = Effectively another microprocessor on the same chip that can execute instructions independently.

Embedded System =  A computer system that is made up of both hardware and software that doesn't usually have an operating system.

System Buses = A bus is a set of parallel wires connecting two or more independent components of a computer system in order to pass signals between them.

Address Bus = Carries addresses from the Processor to main memory or other I/O devices in one direction.

Control Bus = Control signals are sent along the control bus to manage what type of data will be travelling to/from memory and the timing  of these operations within the microprocessor.

Data Bus = Carries data/instructions from main memory to the processor (or from other secondary storage devices) to the processor. It is bi-directional (two way).

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Memory and Storage

Primary Storage = Often referred to as main memory, this contains the instructions and data currently in use. Usually RAM.

Secondary Storage  = This category covers devices that provide non-volatile, semi-permanent storage. They can be electrical, magnetic or optical.

Offline Storage = Used to archive data and/or if data needs to be transported.

Cloud Storage = Data is available via online servers. Requires a network (Internet) connection.

Volatile Storage = Data is lost when the power is switched off.

Virtual Memory = Used when there isn’t enough main memory (RAM) to store all the running programs and data. Pages of main memory and moved to and from a swap space on secondary storage.

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Wired and Wireless Networks 1

LAN  = Local Area Network is where computers are connected together over a small geographical area such as a single building or a single site/campus.

WAN = Wide Area Network is where computers are connected over a large geographical area. This could be several buildings/sites or even between countries.

Client Server Networks = The network relies on a central server and all clients (devices) request services from the server (e.g. print services / file services).

Peer-to-Peer Networks = All computers have equal status and each device can act as a client and a server. All devices can request and provide network services.

Packets = Data transmitted over a network is broken down into packets. Each packet contains the IP address of the sender, the receiver (IP addresses) and the time to live.

WAP = A Wireless Access Point allows wireless devices to access a LAN. WAPs provide Internet access in public places (often known as Wi-Fi hotspots).

Router = An interconnection device used on networks to connect two or more devices. Routers contain a routing table which has a list of IP addresses and common routes for packets to take.  

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Wired and Wireless Networks 2

Switch = A switch is an interconnection device that connects two or more devices together and helps in solving the issue of data collisions. As a data packet arrives at the switch, its destination address is examined and the switch creates a direct connection to that device.

NIC = A network interface card allows a computer to connect to a wired network allowing data packets to travel to and from a computer. It has a MAC or physical hardware address.

DNS = A Domain Name Server has a list of all domain names and their associated IP addresses allowing URLs to be converted to IP addresses.

Virtual Network = Computers on a virtual network share the same network hardware and cabling but software determines what the different virtual networks can access.

Virtual Private Network = Virtual Private Networks use the Internet to create a virtual network to connect organisations.

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Network Topologies, Protocols and Layers 1

Mesh Network Topology = Where some or all of the workstations or other devices are connected directly to each of other. Most are usually connected to the node that they exchange the most data with.

Star Network Topology = In a star network, each device is connected by an individual cable directly to a server or switch. They tend to be the most reliable of the topologies because a failure should only affect one device.

WiFi = Wireless Frequency where packets are transmitted via radio waves. It is slower and more vulnerable to attack but it removes the need for cabling.

Encryption = Encryption is a method of scrambling plain text with a key code to create secure cypher text.

SSL = Secure Socket Layer is an encryption method to keep web connections safe.

IP Address = An Internet Protocol address is unique string of numbers separated by full stops that identifies each computer on a network.

Private IP Addresses = to and to and to are reserved for use on private LANs.

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Network Topologies, Protocols and Layers 2

MAC Address = A Media Access Control address uniquely identifies a device on a network by identifying the network adapter that the device is using. 

Network Protocols = Network protocols are a set of rules or conventions which control the communication between devices on a network.

TCP/IP = Transmission Control Protocol over Internet Protocol. The most commonly used protocol used in both LANs and the Internet.

HTTP = Hypertext Transfer Protocol is used to communicated between web servers and browsers.

HTTPS = Hypertext Transfer Protocol (Secure) provides secure communication between web servers and browsers.

FTP = File Transfer Protocol is used to upload and download files from servers.

POP3 = Post Office Protocol 3 is a simple email protocol that allows you to download messages.

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Network Topologies, Protocols and Layers 3

IMAP = Internet Message Access Protocol is an email protocol that stores email messages on a mail server but allows the end user to view and manipulate the messages as though they were stored locally on the end user's computing device

SMTP = Simple Mail Transfer Protocol allows the user to send email messages.

Network Layers = The OSI networking model has layers that represent everything from the physical connection (voltages etc.) through to the application layer (programs that run via the network).

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System Security 1

Malware = Malware (a portmanteau for malicious software) is any software intentionally designed to cause damage to a computer, server or computer network.

Trojan Horse = A Trojan Horse is software that purports to be for one purpose but contains some sort of malware or payload.

Virus = A computer virus is self replicating code.

Worm = A computer worm is code that replicates and spreads via a computer network.

Phishing = Phishing is the fraudulent attempt to obtain sensitive information such as usernames, passwords and credit card details, often for malicious reasons, by disguising as a trustworthy entity in an electronic communication.

Social Engineering = The use of deception to manipulate individuals into divulging confidential or personal information that may be used for fraudulent purposes.

Brute Force Attacks = A Brute Force Attack is the simplest method to gain access to a site or server (or anything that is password protected). It tries various combinations of usernames and passwords again and again until it gets in. 

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System Security 2

DDoS = A Distributed Denial of Service is a type of attack where multiple compromised systems, that are often infected with a Trojan, are used to target a single system.causing a Denial of Service (DoS) attack. 

SQL Injection = SQL Injection is a very commonly exploited web application vulnerability that allows malicious hackers to steal and alter data in a website's database. 

Network Policy = A network security policy is a document that outlines rules for computer network access, determines how policies are enforced and lays out some of the basic architecture of the company security environment. 

Penetration Testing = Penetration testing (also called pen testing) is the practice of testing a computer system, network or Web application to find vulnerabilities that an attacker could exploit. 

Network Forensics = Network forensics is a branch of digital forensics relating to the monitoring and analysis of computer network traffic for the purposes of information gathering, legal evidence, or intrusion detection. 

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System Security 3

Firewall = A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. A firewall typically establishes a barrier between a trusted internal network and untrusted external network, such as the Internet. 

User Access Levels = Part of an access control procedure for computer systems that allows a system administrator to set up a hierarchy of users. Thus, the low level users can access only a limited set of information, whereas the highest level users can access the most sensitive data. Also called access rights.

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System Software

System Software = A type of computer program that is designed to run a computer's hardware and application programs. It is the interface between the hardware and user applications.

Operating System = An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs.

Defragmentation = Defragmentation is the process of locating the noncontiguous fragments of data into which a computer file may be divided as it is stored on a hard disk, and rearranging the fragments and restoring them into fewer fragments or into the whole file.

Full Backup =  A full back up refers to copying into an archive file of computer data so it may be used to restore the original after a data loss event. 

Incremental Backup = An incremental backup is one in which successive copies of the data contain only the portion that has changed since the preceding backup copy was made.

Open Source Software = the source code is released under a license in which the copyright holder grants users the rights to study, change, and distribute the software to anyone and for any purpose. It may be developed in a collaborative public manner.

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Legal Concerns

Data Protection Act (1998) = A United Kingdom Act of Parliament designed to protect personal data stored on computers or in an organised paper filing system. The Act defined eight data protection principles to ensure that information was processed lawfully.

Computer Misuse Act (1990) = It is designed to protect computer users against wilful attacks and theft of information. Offences under the act include hacking, unauthorised access to computer systems and purposefully spreading malicious and damaging software (malware)

Copyright, Designs and Patents Act (1988) = It is the current UK copyright law. It gives the creators of literary, dramatic, musical and artistic works the right to control the ways in which their material may be used.

Creative Commons Licensing = It is one of several public copyright licenses that enable the free distribution of an otherwise copyrighted work. A CC license is used when an author wants to give people the right to share, use, and build upon a work that they have created.

Freedom of Information Act (2000) = It provides public access to information held by public authorities. It does this in two ways: public authorities are obliged to publish certain information about their activities; and. members of the public are entitled to request information from public authorities.

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