Multi processing systems

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real and pseudo parallelism
Parallelism: Physically simultaneous processing is term as parallelism. It involves multiple processing elements and/or independent device operations.
Concurrency: Logically simultaneous processing is term as Concurrency. It does not imply multiple processing elements (PEs). It requires interleaved execution on a single PE.


Types of parallel Processor Systems


A taxonomy first introduced by Flynn [FLYNN72] is still the most common way of categorizing systems with parallel processing capability. Flynn proposed the following categories of computer systems.
1. Single instruction, single data (SISD) stream: A single processor executes a single instruction stream to operate on data stored in a single memory. Uniprocessors fall into this categories.


Instruction Level Parallelism
There are two fundamental ways of increasing a processor’s instruction execution rate: by increasing clock speed, which decreases the overall execution time per instruction, or by increasing the number of instruction that are executing simultaneously. The former approach relies largely in improvements in IC technology – things such as decreased feature size – that permit higher clock speeds, and as such are out of the hands of the computer desiner. The latter approach is an architecural one, and very much the province of the architect and logic designer.