Computer Architecture 1 CPU IAS (The computer’s main memory) Store (e.g. Disk, DVD) Input/output Interfaces Clock Bus Keyboard, printer, mouse monitor, etc.

Computer Architecture 2  The Bus consists of a system of wires which allow communication between the parts of the computer  There are 3 types of Buses:  Data bus (carries data)  Address bus (carries an address so that data can be found or written to a specific location)  Control (determines whether data is read or written to a location)

Computer Architecture 3 The parts of the CPU Control Unit Accumulator ALU (Arithmetic Logic Unit) PC (Program Counter) MAR (Memory Address Register) CIR (Current Instruction Register) MDR (Memory Data Register) Registers The Internal Bus (not shown) conveys data between the parts

Computer Architecture 4a  The Clock produces pulses (electrical square waves) which are used to synchronise the activity of the parts of the CPU; data being moved at each pulse  The Internal Bus is a system of wires forming a pathway for the movement of data within the CPU  The Control Unit controls the movement of data in the CPU rather like Air Traffic Control at an airport controls the movement of aircraft. It does this by opening and closing pathways within the CPU to enable data to be moved to the correct destination

Computer Architecture 4b  The Accumulator is a place where the results from a calculation can be stored temporarily before being used again for storage or in another calculation  The Arithmetic Logic Unit is used to perform calculations. The range of calculations it can perform is called its Instruction Set  The Registers are used to temporarily store addresses and data which have been received or about to be sent to the Immediate Access Store.

Computer Architecture 5  Modern computers can use both instructions and data which are both stored in their memory. Such computers are known as having “Von Neumann architecture” after John Von Neumann (pronounced noiman) who first proposed this design in 1945 while working on the Manhattan Project  The best way to visualise how the parts of the CPU act to process data is to study the Fetch/Execute Cycle  The Fetch/Execute Cycle is the process of sequentially bringing instructions and data to the CPU during the running of a computer program. (See “Fetch/Execute Cycle”)