OCR GCSE COMPUTER SCIENCE 9 - 1 (COMPONENT 1) WITH 100% CORRECT ANSWERS

CPU Central Processing Unit: The main part of the computer, consisting of the registers, ALU and control unit. Von Neumann Architecture Traditional computer architecture that forms the basis of most digital computer systems. Instructions are fetched, decoded and executed one at a time. Brainpower Read More MAR Memory Address Register: Holds the address of data ready for use by the memory data register. or the address of an instruction passed from the program counter. Step 2 of the fetch, decode, execute cycle. MDR Memory Data Register: Holds the data fetched from or to be written to the memory. Step 3 of the fetch, decode, execute cycle. PC Program Counter: Holds the address of the next instruction. Step 1 of the fetch, decode, execute cycle. Accumulator Holds the result of calculations. ALU Arithmetic Logic Unit: Performs calculations e.g. x = 2 + 3 and logical comparisons e.g. IF x > 3 in the CPU. CU Control Unit: Decodes instructions. Sends signals to control how data moves around the CPU. Cache Memory in the processor providing fast access to frequently used instructions and data. F-D-E cycle Fetch-Decode-Execute Cycle: The complete process of retrieving an instruction from store, decoding it and carrying it out. Also known as the instruction cycle. Clock Speed Measured in Hertz, the clock speed is the frequency at which the internal clock generates pulses. The higher the clock rate, the faster the computer may work. The clock is the electronic unit that synchronises related components by generating pulses at a constant rate. Cache Size A part of the main store between the central processor and the rest of the memory. It has extremely fast access, so sections of a program and its associated data are copied there to take advantage of its short fetch cycle. The larger the size of the cache the more that can be copied and stored here without having to go back to slower main memory (RAM), this has a significant impact on the speed of processing. Cores A part of a multi-core processor. A multi-core processor is a single component with two or more independent actual CPUs, which are the units responsibly for the fetch-decode-execute cycle. Embedded System A computer which has been built to solve a very specific program and is not easily changed. For example the operating system placed inside a washing machine, microwave or set of traffic lights. RAM Random Access Memory: Volatile (data lost when power is off) Read and write. Purpose: temporary store of currently executing instructions and their data. E.g. applications and the operating system in use. ROM Read Only Memory: Non-volatile (data retained when power is off) Read only. Purpose: stores instructions for starting the computer called the bootstrap. Virtual Memory Using part of the hard disk as if it were random access memory. Allows more applications to be open than physical memory could hold. Flash Memory Solid state (no moving parts). Faster than a hard disk drive. Robust. Used to store the BIOS. Secondary Storage Permanent storage of instructions and data not in use by the processor. Stores the operating system, applications and data not in use. Read/write and non-volatile. Optical Storage CD/R, CD/RW, DVD/R, DVD/RW Use: music, films and archive files. Low capacity. Slow access speed. High portability. Prone to scratches. Low cost. Magnetic Storage Hard disk drive. Use: operating system and applications. High capacity. Medium data access speed. Low portability (except for portable drives). Reliable but not durable. Medium cost. Solid State Storage Memory cards & solid state hard drive (SSD). Use: digital cameras and smartphones. Medium capacity. High portability. Reliable and durable. No moving parts. Fast data access speed. High cost. Storage Capacity The amount of data a storage device is able to store. Storage Speed The read/write access speed of a storage device. Storage Portability How easy it is to transport a given storage medium. E.g. Solid state and optical storage and designed to be highly portable, whereas more traditional magnetic storage is designed to stay in place. Storage Durability How resistant to damage and wear a tear a storage device is. Devices with low durability will wear out easily over time. Storage Cost The relative price of a storage medium on a LAN Local Area Network: Small geographic area. All the hardware for the LAN is owned by the organisation using it. Wired with UTP cable, fibre optic cable or wireless using routers and Wi-Fi access points. WAN Wide Area Network: Large geographic area. Infrastructure is hired from telecommunication companies who own and manage it. Connected with telephone lines, fibre optic cables or satellite links. Client-Server Network A client makes requests to the server for data and connections. A server controls access and security to one shared file store. A server manages access to the internet, shared printers and email services. A server runs a backup of data. Peer-to-Peer Network All computers are equal. Computers serve their own files to each other. Each computer is responsible for its own security and backup. Computers usually have their own printer. Stand-Alone Computer A single computing device not connected to any other on a network, either wired or wireless. WAP Wireless Access Point: A networking hardware device that allows a Wi-Fi device to connect to a wired network. Router / Switch In packet-switched networks such as the internet, a router is a device or, in some cases, software on a computer, that determines the best way for a packet to be forwarded to its destination. NIC Network Interface Controller: A computer hardware component that connects a computer to a computer network. Transmission Media The physical media over which data is transmitted, e.g. twisted copper cable, fibre optic etc. DNS Domain Name System: Hosting Websites stored on dedicated servers. Reasons include: Websites need to be available 24/7. Accessed by thousands of users at a time. Strong protection from hackers. They need an IP address that doesn't change. The Cloud Remote servers that store data that can be accessed over the internet. Advantages: Access anytime, anywhere from any device. Automatic backup. Collaborate on files easily. Virtual Networks A logical software based network. Advantages: + Increased security, including more secure access to the network remotely. + The network can easily be expanded with less impact on the infrastructure and cost. + Log in to work from home. Star Network Topology Computers connected to a central switch. If one computer fails no others are affected. If the switch fails all connections are affected. Mesh Network Topology Switches (LAN) or routers (WAN) connected so there is more than one route to the destination. e.g. The Internet More resilient to faults but more cable needed. WiFi Wireless connection to a network. Requires a wireless access point or router. Data is sent on a specific frequency. Each frequency is called a channel. Frequency The number of occurrences of a repeating event per unit of time. Data is set on a specific frequency over a WiFi connection. Channels Each given signal frequency on a WiFi connection is known as a channel. Encryption Encoding readable data called plaintext into unreadable data called ciphertext. Only the intended recipient can decode the data using a key. Protects communications from hackers. Ethernet A standard for networking local area networks using protocols. Frames are used to transmit data. A frame contains the source and destination address, the data and error checking bits. Uses twisted pair and fibre optic cables. A switch connects computers together. IP Address Internet Protocol Address: A unique string of numbers separated by full stops that identifies each computer using the Internet Protocol to communicate over a network.