Pentium (original)

Lore & Background

The P5 microarchitecture was designed by the same Santa Clara team that designed the 386 and 486. Design work started in June 1989; the team decided to use a superscalar RISC architecture which would be a convergence of RISC and CISC technology, with on-chip cache, floating-point, and branch prediction. Vinod Dham, then Vice President of the Microprocessor Product Group and General Manager of Microprocessor Division 5/7, had the concept of using RISC technology in the existing x86 architecture. The preliminary design was first successfully simulated in 1990, followed by the laying-out of the design. By late 1990, the team found that the planned feature could not fit into the die, requiring a redesign to slim down the circuit features without sacrificing performance. In spring of 1991, the die underwent another slimming procedure until Dham was satisfied. By February 1992, the design was taped out, completed by April 1992, at which point beta-testing began. Intel first planned to demonstrate the P5 in June 1992 at PC Expo and to formally announce it in September 1992, but design problems forced the demo to be cancelled and the official introduction delayed until spring 1993. The first computer systems featuring the Pentium appeared in the summer of 1993, the first being Advanced Logic Research's Evolution V workstation, released in the first week of July 1993.

The name 'Pentium' is originally derived from the Greek word pente, meaning 'five', a reference to the prior numeric naming convention of Intel's 80x86 processors (8086–80486), with the Latin ending, since the processor would otherwise have been named 80586. Intel used the Pentium name instead of 586 because in 1991 it had lost a trademark dispute over the '386' trademark, when a judge ruled that the number was generic. The company hired Lexicon Branding to come up with a new, non-numeric name.

Competitors included the superscalar PowerPC 601 (1993), SuperSPARC (1992), DEC Alpha 21064 (1992), AMD 29050 (1990), Motorola MC88110 (1991) and Motorola 68060 (1994), most of which also used a superscalar in-order dual instruction pipeline configuration, and the non-superscalar Motorola 68040 (1990) and MIPS R4000 (1991).

Reader's Guide

The P5 Pentium is significant as the first superscalar x86 processor, demonstrating that a tightly pipelined dual-pipeline design was feasible for the complex x86 instruction set, contrary to the claims of some RISC proponents. Its dual integer pipeline design allowed it to often execute two instructions per clock cycle, while its redesigned floating-point unit was noted to be ten times faster than its predecessor. The processor also introduced a wide 64-bit burst-mode data bus, separate code and data caches, and better support for multiprocessing, being the first x86 CPU with hardware support for it, similar to IBM mainframe computers. Intel worked with IBM to define this ability. The Pentium was succeeded at the workstation and server markets by the P6-based Pentium Pro in November 1995. In January 1997, the Pentium MMX was released, complementing the same basic microarchitecture with the MMX instruction set, larger caches, and other enhancements. It was succeeded at the top range by the Pentium II brand, while production of the P5 Pentium processors continued as low-end series until July 1999, when it was replaced by the Celeron processor, which had also replaced the 486 brand. Intel's Larrabee multicore architecture project uses a processor core derived from a P5 core (P54C), augmented by multithreading, 64-bit instructions, and a 16-byte wide vector processing unit. Intel's low-powered Bonnell microarchitecture employed in early Atom processor cores also uses an in-order dual pipeline similar to P5.

Did You Know?

• Its dual integer pipeline design was argued by some academics and RISC competitors to be impossible for a CISC instruction set.
• The name 'Pentium' comes from the Greek word pente (meaning 'five') with a Latin ending, as it would have been named 80586 under the prior convention.
• Intel lost a trademark dispute over the '386' trademark in 1991, leading to the use of the Pentium name instead of 586.