Question

Explain flynn classifications of various computers based on notions of instructions and data streams.

Answer 1

FLYNN'S CLASSIFICATION

In 1966, Michael Flynn proposed a classification for computer architectures based on the number of instruction steams and data streams (Flynn’s Taxonomy).

· Flynn uses the stream concept for describing a machine's structure.

· A stream simply means a sequence of items (data or instructions).

· The classification of computer architectures based on the number of instruction steams and data streams (Flynn’s Taxonomy).

Flynn’s Taxonomy

· SISD: Single instruction single data

– Classical von Neumann architecture

· SIMD: Single instruction multiple data

· MISD: Multiple instructions single data

– Non existent, just listed for completeness

· MIMD: Multiple instructions multiple data

– Most common and general parallel machine

SISD

· SISD (Singe-Instruction stream, Singe-Data stream)

· SISD corresponds to the traditional mono-processor ( von Neumann computer). A single data stream is being processed by one instruction stream

· A single-processor computer (uni-processor) in which a single stream of instructions is generated from the program.

SIMD

· SIMD (Single-Instruction stream, Multiple-Data streams)

· Each instruction is executed on a different set of data by different processors i.e multiple processing units of the same type process on multiple-data streams.

· This group is dedicated to array processing machines.

· Sometimes, vector processors can also be seen as a part of this group.

MISD

· MISD (Multiple-Instruction streams, Singe-Data stream)

· Each processor executes a different sequence of instructions.

· In case of MISD computers, multiple processing units operate on one single-data stream .

· In practice, this kind of organization has never been used

MIMD

· MIMD (Multiple-Instruction streams, Multiple-Data streams)

· Each processor has a separate program.

· An instruction stream is generated from each program.

· Each instruction operates on different data.

· This last machine type builds the group for the traditional multi-processors. Several processing units

operate on multiple-data streams

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