Finally -- A Choice of CPUs

New PowerPC speed demons and Klamath competitors from AMD and Cyrix.

Mark Carroll and Tom Thompson

Unlike last year, when Intel had the PC-processor market mostly to itself, consumers this year have a choice of CPUs. Whether they will take advantage of the new competition though remains to be seen.

Intel's offerings are the benchmark by which to judge the market. Its P55C on the Pentium level and Klamath on the P6 level will be the best-selling CPUs this year. This won't necessarily be because of pricing or performance considerations. Rather, it's a result of the company's "Intel inside" marketing and the fact that it's the largest OEM mainboard manufacturer in the world. For the record, though, the P55C delivers two instructions per clock cycle at 2 00 MHz with no speculative execution. Klamath offers three instructions per clock cycle at 266 MHz with speculative execution. Both are 32-bit CPUs with 2X8 registers, 2X16 on-chip caches, 64-bit memory, and secondary cache buses.

Challenging Intel in terms of price and performance are this year's offerings from Cyrix and AMD. Both chips offer performance almost at the level of Klamath at a price similar to the P55C or about 30 percent less than Klamath. Like Intel's offerings, Cyrix's M2 and AMD's K6 are 32-bit CPUs with 2X8 registers, 64-bit memory, and secondary cache buses. Both chips have speculative execution. The M2 processes two instructions per clock cycle, but the K6 offers four. Clock speeds are 225 MHz for both. The on-chip caches for both chips are superior to Intel's at 2X32.

RISC processors offered by IBM/Motorola, Exponential Technology, and Digital Microelectronics handily trounce Intel CPUs in performance and clock speed. PowerPC 603e and 604e proces sors available from IBM and Motorola start at about 250 MHz and are now reaching 300 MHz. Exponential's X704, a PowerPC-licensed design, races along at speeds of 466, 500, and 533 MHz. Additionally, IBM and Motorola have announced the first in a series of next-generation PowerPC processors, code-named G3. The first G3 will be targeted at mobile and high-performance desktop systems. It uses the 604e's dynamic branch prediction to boost its performance, and one version of the processor provides direct L2-cache support for high-end designs. At 250 MHz, the G3 consumes only 5 W of power, making it suitable for notebooks. One version of the G3 is pin-compatible with the 604e.

Expect to see G3-based systems about midyear. Because the G3 has little multiprocessor support, the 604e will still handle multiprocessor systems, while the 603e will be found in low-cost systems. However, the 603e is available at brisk 240-MHz speeds and is expected to reach 300 MHz this year -- not bad for a low-end processor. Despite the higher clock speeds, the PowerPC and G3 processors are relatively inexpensive to manufacture, which translates into cost savings for systems designers. The Exponential X704's high speed comes from a hybrid bipolar and CMOS process with higher manufacturing costs. Exponential will also charge a premium for those demanding the X704's ultra high-end performance: about US$1000 in large-volume orders of the 533-MHz chip.

Digital Microelectronics' CPUs are the performance and price top of the line. Thanks to Microsoft, these chips are compatible with Windows NT and its applications, making them a definite choice in the server market. Currently, the company offers the Alpha 21164, which processes data in 64-bit packages and four instructions per clock cycle. It has a 500-MHz clock speed. Registers are 2X32, and both secondary cache and memory buses are 128 bits. In the fourth quarter, Digital Microelectronics will offer the 21264, taking CPU performance to new levels. This chip is planned to offer similar specs as the 21164, but with speculative execution at six instructions per clock cycle with a clock speed of 600 MHz. Intel will remain on top this year in terms of volume, but at least consumers now have a choice.