Processors have a long history behind them. At the beginning there was exactly one data processing logic unit on a processor chip, often referred to as a CPU, but this has fundamentally changed in the mean time. Most processor chips are now equipped with several data processing logic units. Multiple so called processor cores (or cores) are implemented on a single chip. In the past, the term processor was often used as a synonym for the data processing logic unit or CPU, although a processor is an electronic component. In the meantime, a conceptual distinction is made between the processor as an electronic component and the data processing logic units (processor cores), several of which can be accommodated on one processor.

In many contexts, however, the term processors continues to be used, although what is actually meant is the data processing logic unit and thus the processor core. Strictly speaking, the dedicated processor in the previous chapters is generally not a physical processor at all, but only one of the processor cores on a modern processor.

Originally, only one instruction sequence (thread) could run at a time on a CPU (today the processor core). In the meantime, however, many processor cores support the parallel processing of several instruction sequences (threads). This is known as Simultaneous Multi-Threading or SMT for short. Under AIX as the operating system, these are referred to as logical processors, so that up to 8 different threads can be processed at the same time on the same processor core.