Introduction to Concurrency in Programming Languages

Historical Context and Evolution of Languages 119

exist: either singleton (“Single”) or sets (“Multiple”). Given two possibilities

for each dimension, four combinations exist.

• Single Instruction, Single Data stream (SISD): A single program counter

executes on the system, pairing each instruction with at most a single el-

ement from memory. Traditional single CPU architectures such as early

IBM mainframes and personal computers are of this form. These dom-

inated the computing world, especially in the consumer domain, until

only recently.

• Single Instruction, Multiple Data stream (SIMD): A single program

counter executes an instruction stream with multiple data elements be-

ing paired with each instruction. Early vector computers that could

perform ...