Advantages Aand Disadavantages of the Von Neumann Architecture Discussed

Computer Architectures

What the specification says describe classic Von Neumann architecture, identifying the need for, and the uses of, special registers in the functioning of a processor; describe, in simple terms, the fetch/decode/execute cycle, and the effects of the stages of he cycle on specific registers; discuss co-processor, parallel processor and array processor systems, their uses, advantages and disadvantages; describe and distinguish between Reduced Instruction Set Computer (RISC) and Complex instruction Set Computer (CISC) architectures.

Von Neumann Architectures
John Von Neumann realised that the programs and their data were indistinguishable, and therefore can be stored in the same memory. He created a new architecture that contained a single processor which follows a linear sequence of the fetch-decode-execute cycle. In order to do this it has a few special registers. A register is just an area to store data. The individual locations in the memory are registers, but as they have no special purpose they are not special registers. There are five special registers that are used to control the fetch-decode-execute cycle. They are outlined as below:  PC - Program Counter  CIR - Current Instruction Register  MAR - Memory Address Register  MDR - Memory Data Register  Accumulator The specification requires you to know the fetch-decode-execute cycle and how it links in with the special registers in some detail Fetch 1. The PC stores the address of the next instruction which needs to be carried out As instructions are held sequentially in the memory, the value in the PC is incremented so that it always points to the next instruction. 2. When the next instruction is needed, it's address is copped from the PC and placed in the MAR 3. The data which is stored at the address in the MAR is then copied to the MDR 4. Once it is ready to be executed, the