Superscalar - History

History

Seymour Cray's CDC 6600 from 1965 is often mentioned as the first superscalar design. The Intel i960CA (1988) and the AMD 29000-series 29050 (1990) microprocessors were the first commercial single-chip superscalar microprocessors. RISC CPUs like these were the first microprocessors to use the superscalar concept, because the RISC design results in a simple core, thereby allowing the inclusion of multiple functional units (such as ALUs) on a single CPU in the constrained design rules of the time (this was why RISC designs were faster than CISC designs through the 1980s and into the 1990s).

Except for CPUs used in low-power applications, embedded systems, and battery-powered devices, essentially all general-purpose CPUs developed since about 1998 are superscalar.

The P5 Pentium was the first superscalar x86 processor; the Nx586, P6 Pentium Pro and AMD K5 were among the first designs which decode x86-instructions asynchronously into dynamic microcode-like micro-op sequences prior to actual execution on a superscalar microarchitecture; this opened up for dynamic scheduling of buffered partial instructions and enabled more parallelism to be extracted compared to the more rigid methods used in the simpler P5 Pentium; it also simplified speculative execution and allowed higher clock frequencies compared to designs such as the advanced Cyrix 6x86.