therboards for Mac clones become available, the 250-MHz 604e is constrained by a processor-to-main-memory (aka system) bus that runs at 50 MHz, compared to 66 MHz for the current Pentium II system bus. Faster system-bus speeds (and also faster L2-cache bus speeds) are expected from the Intel and PowerPC camps over
the next two years.
With the Pentium II, Intel increased the L1 cache size from 16 to 32 KB, added multimedia extensions (MMX) support, and ratcheted up the speed to 266 MHz. The Pentium II has a 512-KB L2 cache, but Intel may later release Pentium IIs with different L2-cache sizes. The Pentium II system provided by Polywell (800-999-1278) was a screamer. But the Pentium II sacrifices performance in certain areas to allow a lower price and sets the stage for a battle over PC motherboard designs.
The Pentium II sports a new package, the Single Edge Contact (SEC) cartridge, which looks like a deck of playing cards painted black and mounted on edge. The new package allows the use of standard static RAM (SRAM), which is a major reason why Intel can offer the 266-MHz Pentium II at $775 and the 233-MHz Pentium II at $636. (The 512-KB Pentium Pro [200 MHz] cost $1035 at press time, in quantities of 1000.)
However, the Pentium Pro's custom cache ran at the same speed as the CPU, as
high as 200 MHz, whereas the 266-MHz Pentium II's L2 cache bus runs at just 133 MHz. The SEC approach also needs a different socket than the Socket 7 used for the Pentium. Intel claims the SEC cards are needed to support higher clock speeds (greater than 300 MHz) in high volumes at commodity prices. Intel's competitors claim they can match or exceed Intel's performance by sticking with the Socket 7, while still beating Intel's prices.
AMD uses the Socket 7 for its K6 processor announced and released in April. AMD contends that system vendors can build relatively inexpensive systems by leveraging the existing low-cost infrastructure for Socket 7-compatible components. Motherboard vendors who want to support the K6 only need to upgrade the BIOS and clock speed to accommodate the new chip, which is also available at 166 and 200 MHz. The Socket 7 implementation is limited to a 66-MHz shared system and secondary cache bus, however, unlike the Pentium II, which has separate buses. Any motherboard that suppor
ts the P55C pin-out of the Pentium with MMX will probably support the K6, so expect a lively market in K6 upgrades for existing midspeed (120- to 166-MHz) Pentium systems.
The quantity-1000 price for the 233-MHz K6 is $469, or $167 less than the 233-MHz Pentium II. The K6 doesn't have an integrated L2 cache, but 512 KB of L2-cache memory costs only about $25.
The BYTEmark
FPU test
indicates that the K6's primary weakness is in floating-point operations. AMD says most business tasks do not rely heavily on floating-point performance and even contends that the SYSmark for Windows NT 4.0 test suite of five applications uses more floating-point operations than typical users would in using those applications. The K6's performance in the BYTEmark integer test suite showed that while the floating-point performance of the K6 fell slightly short of a 200-MHz Pentium, the K6's integer performance was almost equal to that of the Pentium II.
In our Photoshop tests, which do not emph
asize hard drive or video adapter performance (for a full description, see "MMX: Better in Fits and Starts," February BYTE, page 26), the K6 was slower than the Pentium II in the MMX-intensive RGB-to-CMYK conversion, Unsharp Mask, and Gaussian Blur operations, in some cases by a wide margin. This suggests that AMD's MMX implementation is not quite as fast as Intel's.
As usual, chip and system vendors will continue to release faster products this year and next. Cyrix, another Intel rival, will soon announce its M2 chip, which will have its own MMX implementation. Intel already plans to release a 300-MHz Pentium II this summer. Intel also says that the Pentium II's dual-independent bus architecture supports the evolution of today's 66-MHz system bus to 100 MHz within a year. Meanwhile, in the PowerPC arena, sources say a 604e-like CPU code-named Arthur that will have separate secondary cache and system buses (with the cache bus running at up to the same speed as the CPU) will appear this summer. Exponenti
al's x704 is slated to appear this summer running in the 400-MHz range (with systems possibly using an in-line-cache approach to deliver faster cache-bus performance).
In the meantime, if you want a relatively inexpensive but high-performing system, check out K6-based computers. For the fastest in x86 performance, go with a Pentium II-based system, though if you need workstations or servers with more than two CPUs, you'll have to go with Pentium Pro (greater than dual Pentium II-based systems won't be supported until early 1998, Intel says). As for Mac versus Wintel, our tests show that systems based on the fastest x86 and PowerPC processors are roughly comparable in raw performance. The debate over which OS -- Windows or the Mac -- is better is beyond the scope of this article.
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BYTE ran three series of tests on five systems. All systems had 64 MB of RAM. The Photoshop tests do not address disk access or video performance. The PowerPC (Power Computing's PowerTower Pro 250) and K6 systems each had a 1-MB L2 cache. All other systems had a 512-KB cache.
Pentium II: King of the x86 Hill
