Systems architecture - OCRVon Neumann architecture
Von Neumann architecture provides the basis for the majority of the computers we use today. The fetch-decode-execute cycle describes how a processor functions.
Von Neumann architectureA description of the processing architecture that all CPUs use. John von Neumann invented the processor architecture which stores a program in memory as instructions and executes them sequentially using the ALU, control unit and registers. This is known as the stored program concept. is the design upon which many general purpose computerA computer designed to be able to carry out a wide range of instructions. are based. The key elements of Von Neumann architecture are:
dataUnits of information. In computing there can be different data types, including integers, characters and Boolean. Data is often acted on by instructions. and instructionA single action that can be performed by a computer processor. are both stored as binaryA number system that contains two symbols, 0 and 1. Also known as base 2. digits
data and instructions are both stored in primary memoryThe part of a computer that stores data.
instructions are fetched from memory one at a time and in order (serially)
the CPU/processorCentral processing unit - the brain of the computer that processes program instructions. decodes and executes an instruction, before cycling around to fetch the next instruction
the cycle continues until no more instructions are available
A processor based on Von Neumann architecture has five special registerThe section of high speed memory within the CPU that stores data to be processed. which it uses for processing:
program counter - holds the memory address of the next instruction to be fetched from primary memory
memory address register (MAR) - holds the address of the current instruction that is to be fetched from memory, or the address in memory to which data is to be transferred
memory data register (MDR) - holds the contents found at the address held in the MAR, or data which is to be transferred to primary memory
current instruction register (CIR) - holds the instruction that is currently being decoded and executed
accumulator (ACC) – holds the data being processed and the results of processing