GCSE COMPUTER SCIENCE OCR (COMPONENTS TEST QUESTIONS AND ANSWERS)

Computer A machine that processes data. Embedded Systems Computers built into other devices, like dishwashers, microwaves and TVs. Brainpower Read More Previous Play Next Rewind 10 seconds Move forward 10 seconds Unmute 0:11 / 0:15 Full screen CPU Known as the 'brain' of the computer. It processes all of the data and instructions that make the systems work. Characteristics which affect the processing power of the CPU - Clock speed - Number of cores - Cache size Control Unit It is in overall control of the CPU. Its main job is to execute program instructions by following the fetch-decode-execute cycle. Controls the flow of data inside the CPU and outside the CPU. Arithmetic Logic Unit Basically does all the calculations. Performs logic operations such as AND, OR and NOT and binary shifts. Contains the accumulator register. Cache It is a very fast memory in the CPU, but slower than registers. Stores regularly used data so that the CPU can access it quickly the next time it's needed. Has a very low capacity and are expensive. There are different types of levels of memory - L1 (quickest but least amount of capacity), L2 (average speed and capacity) and L3 (slowest but most amount of capacity). Von Neumann architecture Describes a system where the CPU runs programs stored in memory. Programs consist of instructions and data which are stored in memory addresses. Program counter Holds the memory address of the instruction for each cycle. Accumulator Stores intermediate results of calculations in the ALU. Memory Holds the program instructions and the program data. Memory address register Holds any memory address about to be used by the CPU. The address might point to data or a CPU instruction. Memory data register Holds the actual data or instruction. This may have been fetched from memory, or be waiting to be written to memory. Fetch instruction 1. Copy memory address from the program counter to the MAR. 2. Copy the instruction stored in the MAR address to the MDR. 3. Increase the program counter to point to the address of the next instruction, ready for the next cycle. Decode instruction The instruction in the MDR is decoded by the CU. The CU may then prepare for the next step, e.g. by loading values into the MAR or MDR. Execute instruction The instruction is performed. This could be: - load data from memory - write data to memory - do a calculation or logic operation (using the ALU) - change the address in the PC - halt the program Main memory Where all data, files and programs are stored while they're being used. RAM Used as the main memory in the computer. It can be read and written to. It is volatile. When a computer boots up, the operating system is copied from secondary storage to it. When software applications, documents and files are opened, they are copied from secondary storage to it until the files or applications are closed. It is slower than the CPU cache, but way faster than secondary storage. Virtual Memory It is secondary storage used as extra RAM. May be needed if there are too many applications open at once, of if a particularly memory-intensive application is being used. Using it can make a computer slow to respond when switching between applications or when using a memory-intensive application. ROM It is a non-volatile memory. It can only be read, not written to. Comes on a small, factory-made chip built into the motherboard. Contains all the instructions a computer needs to properly boot up called BIOS (Basic Input Output System). Clock speed It is the number of instructions a single processor core can carry out per second (Hz). The higher it is, the greater the number of instructions that can be carried out per second. Number of cores Each core in a CPU can process data independently of the rest. The more cores a CPU has, the more instructions it can carry out at once, so the faster it can process a batch of data. Cache size The larger it is, it gives the CPU faster access to more data it needs to process. GPU It is a specialised circuit for handling graphics and image processing. They relieve the processing load on the CPU, freeing it to do other things. Primary storage Refers to the memory areas that the CPU can access very quickly. Has the fastest read/write speeds and is mostly volatile. Secondary storage It is non-volatile. It is where all data are stored when not in use. Read/write speeds are much slower compared to primary storage. Tertiary storage It is non-volatile. Used for storing data more long term. It's mainly used for archives and back-ups of massive amounts of data. HDD It is the traditional internal storage in PCs and laptops. It is made up of a stack of magnetised metal disks spinning at a rate between 5400 and 15000 rpm (revolutions per minute). Data is stored magnetically in small areas called sectors within circular tracks. It is generally very long lasting and reliable, although they could be damaged by large impacts like being dropped. SSD It is a storage device with no moving parts. Most of them use a type of flash memory. It is used for the same purpose as HDDs - for internal storage. It has significantly faster read/write times than HDDs. Using it it rather than traditional HDD can give much quicker times for booting up and opening programs and files. Advantages of HDDs - HDDs are cheaper. - Both are high capacity, but HDDs are higher. - HDDs have a longer read/write life than SSDs - SSDs can only be written a certain number of times before they begin to deteriorate. Advantages of SSDs - SSDs are faster. - SSDs don't need defragmenting. - SSDs are more shock-proof than HDDs. - HDDs make some noise, SSDs are silent. Optical discs They are cheap and robust secondary storage. They are things like CDs, DVDs and Blu-Ray discs. They come in three forms: - read-only - write-once - rewritable They are very cheap, portable and won't be damaged by water or shocks (although they are easily scratched). Magnetic tape Has much greater storage capacity than HDDs. It also has an extremely low cost per GB. It is often used by large organisations in archive libraries to store huge amounts of data. Add or Remove Terms