Computer Architectures - CIE A-Level Computer Science (15.1.2)

SISD

Single Instruction, Single Data.

SISD architecture

A single processor fetching one instruction at a time and operating on one data source; strictly sequential execution (no parallelism).

SISD common usage

In early personal computers and any system that processes tasks strictly one after another.

SIMD

Single Instruction, Multiple Data.

SIMD system operation

Many "identical" processors all execute the same instruction simultaneously on different pieces of data.

Classic example of SIMD

A graphics card using one small processor per pixel to uniformly increase image brightness across all pixels at once.

Applications benefiting from SIMD

Image-processing, sound sampling, or any task where the same operation must be applied to a large set of independent data items.

MISD

Multiple Instruction, Single Data.

MISD architecture

Multiple processors each run different instructions on the same data stream; very uncommon (e.g. Space Shuttle flight-control used a form of MISD for reliability).

MIMD

Multiple Instruction, Multiple Data.

MIMD differences

Each processor runs its own instruction stream independently and works on its own partition of the data; true general-purpose parallelism.

MIMD usage

In multicore chips, supercomputers, distributed systems—any architecture where tasks and data can be partitioned and scheduled independently.

Parallel-processing software requirements

1) Processors must be able to communicate and transfer processed data between them.