Flynn’s architectural classification scheme

 

·     Basic types of architectural classification:

1.     Flynn’s classification

2.     Feng’s classification

3.     Handler’s classification 

·     Other types of architectural classification:

1.     Classification based on coupling between processing elements

2.     Classification based on mode of accessing memory

Flynn’s architectural classification scheme:

Michael J. Flynn, in 1996, proposed a scheme for computer’s architectural classification. 

Flynn’s taxonomy of computer architecture is based on the notion of a stream of information and is the most popular classification amongst all others which is based on the notion of a stream of information. Instructions and data are the two types of information flow into a processor and different classifications are due to multiplicity of instruction streams and the data streams in computer systems.

Flynn's idea for classification of computer architectures stated that supported the quantity of simultaneous instruction and data streams utilized by CPU during a program execution, digital computers may be classified into four categories. This is popularly called as Flynn's classification of computer architecture. Either of the instruction or data streams can be either be single or multiple According to Flynn’s classification.

Following are the basic terms & statements for better understanding:

• Stream: Stream refers to sequence of objects (may be data or instructions) that's executed by one CPU.

• Instruction Stream: Instruction stream refers to sequence of instructions that's executed by the CPU.

• Data Stream: Data stream refers to the sequence of information including input, partial or temporary results demanded by instruction stream.

• With the help of memory modules Instructions and data can be fetched    

• Data streams flow between processor elements and also the memory bi-directionally.

Computer architecture is classified into the subsequent four distinct types:

• 1.     SISD: Single Instruction stream – Single Data stream;
• 2.     SIMD: Single Instruction stream – Multiple Data stream;
• 3.     MISD: Multiple Instruction stream – Single Data stream; and
• 4.     MIMD: Multiple Instruction stream – Multiple Data stream.

•       SISD: Single Instruction stream – Single Data stream 

In SISD computer architecture execution stages instructions may overlapped but they are executed sequentially. In other words, we can say that pipelining technique can be used in CPU.

Modern day SISD uniprocessor systems are mostly pipelined. Even though SISD computer are under supervision of one control unit but they may contain more than one functional unit in them. Only scalar type instructions can be processed by SISD architectural computers.

Most serial computers available today follow in SISD architecture.

Given below is the diagram depicting SISD computer architecture:

Examples of SISD computers:

• Some of the functional unit used by SSID Computers are IBM 701, IBM 1620, IBM 7090
• IBM 360/91, CDC Star –100, TI-ASC are some of the multiple functional units used by SSID Computers

  

• SIMD: Single Instruction stream – Multiple Data stream

In SIMD computer, we are able to see from the below diagram there are multiple processing elements supervised by the common control unit. All the processing elements, which are ALUs, receive the identical instruction broadcast from the control unit but care for different data sets from distinct data streams. Every processor element gets different instructions for execution on the exact data stream or the adjacent ones. Here the output of one processor elements becomes the input of the subsequent processor element within the series.

Given below is SIMD architecture diagram: 

SIMD computer is used to process vector type data.

Array processor falls into SIMD computer.

PEPE, BSP, Illiac-IV are some of the examples of SIMD computer.

•   MISD: Multiple Instruction stream – Single Data stream

MISD architecture is also known as systolic arrays. 

In MISD computer architecture, there are n processor elements. Every processor element gets different instructions for execution on the exact data stream or the adjacent ones. In this case the input of adjacent processor in the series comes from the output of its predecessor processor.

Given below is the diagram of MISD architecture:

MISD architecture is not that popular though some fault tolerance machines will be employed in this class. And hence, there's no practical machine of MISD class.

•   MIMD: Multiple Instruction stream – Multiple Data stream

MIMD computer category covers not only multiple computer system but also multiprocessor systems.

MIMD computer is of two types:

• tightly coupled or Uniform Memory Access (UMA),
• loosely coupled or Non-Uniform Memory Access (NUMA)

If the degree of interaction among the processor is high then MIMD computer is called tightly coupled or Uniform Memory Access (UMA) and) if the degree of interaction among processors is low then they are called as loosely coupled or Non-Uniform Memory Access (NUMA).

Given below is the MIMD computer architecture diagram:

Examples of MIMD computer:

• Some of the loosely coupled examples of MMID computer are IBM 370/168 MP, Univac 1100/80
• Some of the tightly coupled examples of MMID computers are C.mmp, Cray-3, S-1, Cray-X MP

Team:

1. Rauf Jamadar

2. Sahil Kakurle

3. Kalyani Laddha

4. Abhijeet Kamble

Department of SY Common,

Vishwakarma Institute of Technology, Pune.