OCR Computer Science A Level Paper 1 Exam Questions and Answers

PC Program counter, contains the address of the next instruction CIR Current Instruction Register: stores the address of the next instruction currently being executed and decoded MAR Memory Address Register, holds relevant memory address (to read from or write to) MDR Memory Data Register, stores data being transferred to and from memory, acts as a buffer ALU Arithmetic and Logic Unit, does all mathematical calculations and makes all logical decisions Accumulator A storage register in the ALU that holds data temporarily while the data is processed and before it is transferred to memory. RISC Reduced Instruction Set Computer: Only simple instructions taking one clock cycle are executed - currently more widely used than CISC Advantages: allows for pipelining, execution will be quicker or as fast as CISC Disadvantages: Compiler has to do more work, more RAM required CISC Complex Instruction Set Computer: Large instruction set is used to minimise lines of code required - mainly used for microcontrollers and embedded systems Advantages: compiler has very little work to do, not much RAM required Disadvantages: Building in specialised instructions can be inefficient when only ~20% get used per program GPU Graphics Processing Unit - dedicated graphics processor on a graphics card, used to render images stored in the RAM of the graphics card. Multi-core CPU A CPU with more than one core on the same chip - makes use of parallel processing for optimum efficiency