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Pseudo Fifth-Generation Processors

There is at least one processor that, while generally regarded as a fifth-generation processor, lacks many of the functions of that class of chip—the IDT Centaur C6 Winchip. True fifth-generation chips would have multiple internal pipelines, which is called superscalar architecture, allowing more than one instruction to be processed at one time. They would also feature branch prediction, another fifth-generation chip feature. As it lacks these features, the C6 is more closely related to a 486; however, the performance levels and the pinout put it firmly in the class with Pentium processors. It has turned out to be an ideal Pentium Socket 7–compatible processor for low-end systems.

IDT Centaur C6 Winchip

The C6 processor is a recent offering from Centaur, a wholly owned subsidiary of IDT (Integrated Device Technologies). It is Socket 7–compatible with Intel's Pentium, includes MMX extensions, and is available at clock speeds of 180, 200, 225, and 240MHz. Pricing is below Intel on the Pentium MMX.

Centaur is led by Glenn Henry, who spent more than two decades as a computer architect at IBM and six years as chief technology officer at Dell Computer Corp. The company is a well-established semiconductor manufacturer well-known for SRAM and other components.

As a manufacturer, IDT owns its own fabs (semiconductor manufacturing plants), which will help keep costs low on the C6 Winchip. Its expertise in SRAM manufacturing may be applied in new versions of the C6, which integrate onboard L2 cache in the same package as the core processor, similar to the Pentium Pro.

The C6 has 32KB each of instruction and data cache, just like AMD's K6 and Cyrix's 6x86MX, yet it has only 5.4 million transistors, compared with the AMD chip's 8.8 million and the Cyrix chip's 6.5 million. This allows for a very small processor die, which also reduces power consumption. Centaur achieved this small size with a streamlined design. Unlike competitor chips, the C6 is not superscalar—it issues only one instruction per clock cycle like the 486. However, with large caches, an efficient memory-management unit, and careful performance optimization of commonly used instructions, the C6 achieves performance that's comparable to a Pentium. Another benefit of the C6's simple design is low power consumption—low enough for notebook PCs. Neither AMD nor Cyrix has a processor with power consumption low enough for most laptop designs.

To keep the design simple, Centaur compromised on floating-point and MMX speed and focused instead on typical application performance. As a result, the chip's performance trails the other competitors' on some multimedia applications and games.

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