15.1 Processors, Parallel Processing and Virtual Machines

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Parallel Processing & Flynn's Taxonomy

Definition: Flynn's Taxonomy is a method used to classify computer architectures based on the number of Instruction Streams and Data Streams processed simultaneously. It allows us to distinguish between simple sequential processing and advanced parallel systems.

1. The Two Variables

  • Instruction Stream: A sequence of instructions read from memory and executed by the processor.
  • Data Stream: The actual data values being used as operands for those instructions.

2. The Four Architectures

SISD

Single Instruction, Single Data

One processor, one instruction, one piece of data. This is the classic Von Neumann model.

SIMD

Single Instruction, Multiple Data

One instruction is broadcast to multiple processors, which apply it to different data points at once (e.g., Array Processors/GPUs).

MISD

Multiple Instruction, Single Data

The same piece of data is processed by different instructions on different processors. Primarily used for redundancy in critical systems.

MIMD

Multiple Instruction, Multiple Data

Multiple processors, each executing different instructions on different data. This is the basis for all modern multi-core systems.

⚠️ Exam Note: Classification

If an exam question asks you to classify a Multi-core PC, the answer is MIMD. If it asks about a Graphics Card doing 3D rendering, the answer is usually SIMD.