Scalar processors represent a class of computer processors. A scalar processor processes only one datum at a time, with typical data items being integers or floating point numbers. A scalar processor is classified as a SISD processor (Single Instructions, Single Data) in Flynn's taxonomy.
In contrast, in a vector processor a single instruction operates simultaneously on multiple data items (referred to as "SIMD"). The difference is analogous to the difference between scalar and vector arithmetic.
A superscalar processor, on the other hand, executes more than one instruction during a clock cycle by simultaneously dispatching multiple instructions to redundant functional units on the processor. Each functional unit is not a separate CPU core but an execution resource within a single CPU such as an arithmetic logic unit, a bit shifter, or a multiplier.
- Advanced Microprocessors and Interfacing by Badri Ram 2000 ISBN 0-07-043448-4 page 11