There have been two types of computers fixed program computers and stored program computers. Fixed program computers have very specific functions and they cannot be programmed while stored program computers can be programmed to carry out different tasks, applications are stored on them.
Von Neumann Architecture or Princeton architecture was first published by Jon Von Neumann in 1945. The term “von Neumann Architecture” has evolved to mean any stored-program computer. The document describes a design architecture for an electronic digital computer with different components.
What are these component?
· Control Unit (CU) - it handles all processor control signals. It directs all input and output flow, fetches code for instructions and controlling how data moves around the system.it directs the operation of other units by providing timing and control signals.
· Arithmetic and logical unit (ALU) - the arithmetic and logical unit is the part that handles all the calculations the CPU may need. For example addition, subtraction, comparison, etc. It performs logical operations, bit shifting operations and arithmetic operations. It is a combinational digital electronic circuit.
· Main memory unit-
1. MAR (Memory Address Register) – This register holds the memory location of the data that needs to be accessed.
2. MDR (Memory Data Register) - It holds the data that is being transferred to or from memory.
3. AC (Accumulator) – This register holds the intermediate arithmetic and logic results
4. PC (Program Counter) – It contains the address of the next instruction to be executed.
5. CIR (Current Instruction Register) – This register contains the current instructions during the process.
· Input/ Output Devices – program and data is read into the main memory from the input devices while output devices are used to output the information from the computer, to present it to the user.
· Buses- data is transmitted from one part of a computer to another, connecting all major internal components to the CPU and memory via buses.
1. Address Bus- It carries the address of data between the processor and the memory.
2. Data Bus- It carries data between the processor, the memory unit and the input output devices.
3. Control Bus- It carries signals/commands from the CPU.
How does the Von Neumann Architecture work?
The Von Neumann Architecture works using four simple steps:-
Ø Fetch: - This gets the instructions from the RAM and puts them in the cache to be accessed by the Control Unit.
Ø Decode: - The Control Unit decodes the instructions into a form the Arithmetical and Logical Unit can understand and feeds them to the ALU.
Ø Execute: - The Arithmetic and Logical Unit executes the instructions and outputs the result to the cache.
Ø Store: - Once the program counter says stop, the result is offloaded to the main memory.
Drawbacks of Von Neumann Architecture
§ Instructions can only be carried out one at a time and sequentially. This is commonly referred to as ‘Von Neumann Bottleneck’
§ Risk of an instruction being rewritten due to an error in the program.
§ Parallel implementation is not allowed.
This architecture is very important and is used in our PCs and even in supercomputers.
For more information on Von Neumann Architecture
https://www.microcontrollertips.com/difference-between-von-neumann-and-harvard-architectures/
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