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1.3
Types of Processor (John von Neumann (Instructions and data are…
1.3
Types of Processor
Multi-Purpose Machines
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In the 1940s, John von Neumann and Alan Turing both proposed the stored program concept
Stored program concept
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The instructions are fetched one at a time, decoded and executed sequentially by the processor
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Harvard architecture
An alternative model separates the data and instructions into separate memories using different buses
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Von Neumann architecture
Used in PCs, laptops, servers and high performance computers
Data and instructions share the same memory. Both use the same word length
One bus for data and instructions is a bottleneck
One bus is simpler for control unit design
Harvard architecture
Used in digital signal processing, microcontrollers and in embedded systems such as microwave ovens and watches
Instructions and data are held in separate memories which may have different word lengths. Free data memory can’t be used for instructions, and vice versa
Separate buses allow parallel access to data and instructions
Control unit for two buses is more complicated and expensive
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