Flynn's Taxonomy | Flynn's Classification

 

Flynn’s Taxonomy

This taxonomy proposed by Michael J. Flynn in 1966. Flynn's taxonomy is a “specific classification of parallel computer architectures.” Classifications are based on the number of concurrent instruction (single or multiple) and data streams (single or multiple) available in the architecture. The sequence of instructions read from memory is called an instruction stream. The operations performed on the data in the processor is called a data stream.

 

SISD (Single Instruction Single Data Stream)

Most conventional machines with one CPU containing a single arithmetic – logic unit. SISD computers and sequential computers are same. SISD represents the organization of a single computer containing a control unit, a processor unit, and a memory unit. Instructions are executed sequentially and the system may or may not have internal parallel processing capabilities. In SISD computer instructions are executed sequentially but may overlap in their execution stages.

Figure : Single Insturction Single Data (SISD)

SIMD (Single Instruction Multiple Data Stream)

This category corresponds to array processors. They have multiple processing/execution units and one control unit. SIMD represents an organization that includes many processing units under the supervision of a common control unit. All processors receive the same instruction from the control unit but operate on different items of data.

Figure : Single Insturction Multiple Data (SIMD)

MISD (Multiple Instruction Single Data Stream)

There is no computer at present that can be classified as MISD. Mostly used in pipelined computers. Each receiving distinct instructions operating over the same data stream and its derivatives. The result of one processor become the input of the next processor in the micro-pipe. MISD structure is only of theoretical interest since no practical system has been constructed using this organization.

Figure : Multiple Insturction Single Data (MISD)

MIMD (Multiple Instruction Multiple Data Stream)

Most multiprocessor system and multiple computer system can be classified in this category. In MIMD, there are more than one processor unit having the ability to execute several programs simultaneously. MIMD organization refers to a computer system capable of processing several programs at the same time. Contains multiple processing units. Execution of multiple instructions on multiple data.

Figure : Multiple Insturction Multiple Data (MIMD)

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