Commercial Microprocessors: From a Single Bit to 128 Bits

Summary

This chapter presents the key characteristics of the first generations of microprocessors or microprocessor unit. It discusses the 4‐bit family, 8‐bit family, 12‐bit family, 16‐bit family, and 32‐bit family of microprocessors. The 16‐bit generation marks a turning point because technology makes it possible to implement high‐level concepts such as the (primary) memory protection offered, for example, by virtual memory and the supervisor execution mode, these protections being necessary for modern operating systems. The 32‐bit generation appeared from the early 1980s. It marks the transition to the complementary metal oxide semiconductor technology. Two architectures marked the 1980s. The first is called reduced instruction set computer (RISC) and the second is instruction‐level parallelism. The RISC approach consists mainly of reducing the number of instructions to the bare minimum and optimizing their execution.