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[ Go to May 1997 Table of Contents ]
WinLab Reviews
-- by Jonathan Blackwood and Cynthia Morgan
The K6 isn't simply an Intel knock-off; it's a sophisticated sixth-generation x86 hybrid that seems to have successfully managed design problems that have plagued the Pentium line for years. It's already MMX-enabled (Intel and AMD signed a technology-sharing agreement in January 1996) Despite the similarities in performance, and full Windows compatibility, AMD has chosen a number of different approaches to the design of the K6 as compared to the Pentium Pro. The chip employs larger level 1 caches than its competitor, 32KB for data and 32KB for instructions, for a 64KB total. By comparison, the Pentium Pro uses twin 8KB caches, and the upcoming Pentium II processor will still have two 16KB caches for a total of only 32KB. The AMD processor has seven parallel execution units (including the floating-point and MMX units), and it uses the latest branch prediction, speculative execution and out-of-order execution technologies. It also has a unique 8,192-entry branch history table, which combines with return address stack to deliver a branch prediction accuracy of more than 95 percent-the Pentium Pro averages 90 percent branch prediction accuracy. The K6 also offers something that, at present, Intel's high-performance Pentium family can't: easy integration into existing component designs. Intel's long x86 legacy means the 5.5-million transistor Pentium Pro must fight power and heat problems that weren't a consideration in the early days of much-lower clock speeds. Higher clock speeds require more power; that power produces extra heat, which can eventually degrade the chip into failure. These problems have continued with new Pentium designs, often delaying their debut and right now giving the 8.8-million transistor K6 a temporarily clear field in the over-200MHz x86 market. The K6 design is unencumbered by legacy restraints; preliminary looks show the chip has avoided major heat and power-management problems. Intel continues the Pentium chip family's power-hungry, heat-producing ways, adding new fluctuating voltage requirements for additional energy management to some of its forthcoming chips. The requirements have delayed debut of the chip, and the increased design complexity and component cost could keep processor price curves from dropping as quickly as PC vendors would like. In addition, Intel has attempted to move vendors into a new, modular processor design that allows for quick upgrades without significant retooling. However, PC makers are balking at the cost of the new packaging and the larger size of the new design, especially in the mobile market. There, the design's thickness may prohibit its use in ultra-thin machines. At the value-priced end of the PC market, where manufacturers already operate on extremely thin profit margins, the K6's ability to use off-the-shelf motherboards and chipsets could make it the chip of choice. AMD has pledged to enable other new technologies, such as Intel's Accelerated Graphics Port, by providing chipsets that will work with little modification in inexpensive Socket 7 motherboards already used in today's Pentium PCs. The Pentium Pro, on the other hand, requires a special socket. That, too, will serve to lower the commercial price of a high-performance K6 computer. Put it all together in a low-power, Socket 7-compatible package, and manufacturers can deliver K6 systems with minor modifications and major performance gains.
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