Von Neumann architecture
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Describe the stored program concept when applied to the von Neumann model
• The programme is stored on a secondary storage device • Data and instructions are moved to memory • Data and instructions are stored in the same memory • Data and instructions are moved to registers to be executed • Instructions are fetched one at a time
Explain what is meant by the stored programme concept
• Programs and data are stored in computer memory(2) - Instructions are fetched and executed one at a time.
What is the purpose of the address bus?
It carries and transports the address of the next item or instruction to be fetched. It is unidirectional as data travels one way
What is the purpose of the data bus?
Carries data that is currently being processed (or that has been or that will be). Data can travel in both directions(bi-directional)
What is the purpose of the control bus?
It transports signals. It controls the actions of the processor. Can be unidirectional or bi-directional
What is the function of the Immediate Access Store (IAS)?
Data and instructions are fetched by the CPU and stored here to wait to be processed
Where does the CPU fetch instructions from?
RAM
Describe the role of the Arithmetic Logic Unit(4)
Carries out calculations and logical operations(2) Holds temporary values in a register known as an accumulator during calculations
What is the function of the control unit?
It controls the operation of the memory, processor and input/output devices. An instruction is read from memory and interpreted with the fetch-decode-execute cycle. It sends signals using the control bus to tell other components what to do.
What are the components in a von Neumann model?
ALU, MDR, MAR, Accumulator, IAS, RAM, PC , CIR, Address bus/ data bus/control bus
What is main memory and how is it used in the von Neumann model?
It is RAM (or primary memory or volatile memory) Holds data and instructions that are currently in use. Directly accessible by the CPU