difficult for the next few years. Hibernat
ion is not an option.
While novices continue to blindly compare megahertz and megabytes, knowledgeable users will be juggling many more variables. These are outlined below.
- Intel's fastest Pentium is cruising at 200 MHz this fall, but due to inherent limitations of its aging architecture, it's barely faster than a Pentium-166. Also, the current P54C-series Pentiums don't recognize Intel's new MMX multimedia instructions. Early next year, Intel will address these problems by introducing the new P55C-series Pentiums. But the P55C is still a fifth-generation x86 processor that will appear at a crucial juncture when Intel is attempting to push the mainstream market toward the sixth-generation Pentium Pro.
- Lower prices and new system chip sets are making Pentium Pro-based desktop PCs more affordable. Unfortunately, the Pentium Pro isn't the best choice if you're running 16-bit software, including Windows 95. Also, current Pentium Pros do not support MMX. Intel is readying a n
ew P6-class processor, code-named Klamath, that improves 16-bit performance and supports MMX. But you'll have to wait for it until mid-1997 at the earliest, and the upgrade path for Pentium Pro users is muddy.
- Cyrix's rejuvenated 6x86 handily beats a comparable Pentium, has no trouble with 16-bit code, and boasts the fastest I/O bus in the business. However, Cyrix can't match Intel's fastest core speeds, and the 6x86 doesn't support MMX. In addition, BYTE recently discovered that some revisions of the 6x86 suffer from serious performance problems when running on Windows NT Workstation 4.0.
- Cyrix plans to address all these issues early next year with an improved version of the 6x86, called the M2. But its MMX compatibility will be in question at first because Cyrix doesn't have a licensing agreement for the Intel technology.
- AMD, still struggling with its disappointing K5 series, will finally ship a version that lives up to the company's early promises. But the K5 is hopelessly far behind the
leading edge. In 1997, AMD's hopes will ride on the K6, which is supposed to support MMX and match or exceed the performance of the Pentium Pro. After stumbling with the K5, AMD desperately needs to win back the confidence of system vendors and users.
- A new contender, International Meta Systems (IMS), claims that it will introduce a CPU that fits into Pentium sockets and approximates the performance of a Pentium Pro. IMS has made previous attempts to break into the x86 market, but those products never shipped. This time, IMS is taking a different approach (see the sidebar "IMS Rides Again with the Meta6000").
- Looming on the horizon is Intel's seventh-generation x86, known as the P7 or Merced. It will introduce a 64-bit x86 architecture. However, systems built with this chip probably will not appear until 1998 at the earliest, so the Merced should not affect your near-term plans.
Intel's Introductions
To defend its high profit margins and to keep its huge wafer-fabr
ication plants busy, Intel must periodically abandon an older-generation CPU and steer the market toward the next-generation product. That's what will happen to the Pentium in 1997. Although the Pentium will remain a high-volume product next year, Intel wants users to start thinking of the Pentium Pro as a mainstream CPU. Until now, Intel has mainly positioned the Pentium Pro for servers and workstations.
However, this predictable transition (which happens about every four years) is a little more confusing this time because Intel is simultaneously introducing MMX, an architectural enhancement that spans both generations (see "x86 Enters the Multimedia Era," July BYTE). Because MMX will debut with the Pentium, not the Pentium Pro, users who buy new systems during the transitional phase will have to wrestle with a few more decisions.
MMX will appear first in the P55C-series Pentiums, which are scheduled to begin shipping in the first quarter of 1997. They have improved pipelines and twice as much on-boa
rd cache: 16 KB each for the primary instruction and data caches, compared to the 8-KB caches in previous
Pentiums. As a result, the P55C will outperform a regular Pentium at the same clock speed, even without MMX acceleration. Sources estimate the performance gain to be about 15 percent -- an important point if you're comparing two systems with different Pentiums.
The P55C will likely debut at 200 MHz, but it may run as fast as 233 MHz. Unfortunately, upgrading to a P55C probably won't be as simple as plugging the chip into an existing Pentium socket. Although it's pin-compatible with existing sockets, Intel had to reduce the voltage so that the chip runs cool enough at higher clock speeds. Thus, you'll probably need a new motherboard for the P55C.
Waiting for Klamath
Astute users who want to postpone obsolescence are looking toward the next generation: the Pentium Pro. Unfortunately, this chip has several problems. It bogs down under 16-bit software and won't support MMX un
til after the P55C. It's also expensive, because it uses a multichip module to incorporate a 256- or 512-KB Level 2 (L2) cache in the same package with the CPU die. And it requires more costly system chip sets and six-layer motherboards.
Intel's solutions are the Klamath and new chip sets. Intel isn't talking about Klamath yet, but this P6-class chip will almost certainly eliminate the expensive multichip module. Intel will reportedly offer the Klamath on a small daughtercard that plugs into a special slot on the motherboard. The daughtercard would include the CPU and the L2 cache, and some daughtercards may have sockets for multiple CPUs.
Getting rid of the multichip module would drastically reduce Intel's manufacturing costs. It would also make it easier to upgrade a system, because users could swap daughtercards to get a faster CPU, more cache, or both. That's why Apple started using CPU daughtercards in its high-end Power Macs last year.
But separating Klamath's CPU and L2 cache could have som
e less desirable side effects as well. First, there's the question of performance. The Pentium Pro's L2 cache is closely coupled to the CPU over a dedicated 64-bit bus that runs at the same clock speed as the core. It's an extraordinarily fast bus that contributes a lot to the Pentium Pro's superior 32-bit benchmark results. Moving the L2 cache out of the package may force Intel to adopt a slower bus. If so, Klamath would need a larger cache, higher clock speeds, and perhaps some additional enhancements to compensate for the loss. If Intel puts Klamath on a daughtercard, the bus that connects this card to the motherboard is another potential bottleneck.
Faster Clocks
In any case, Klamath will support MMX and probably include some modifications to enhance 16-bit performance. Higher clock speeds are a certainty, thanks to Intel's new 0.28- and 0.25-micron CMOS processes. In 1997, these smaller processes will supersede the 0.35-micron BiCMOS process on which today's Pentiums and Pentium
Pros are built.
Klamath will debut sometime in 1997 at 0.28 micron, yielding a minimum clock speed of 200 or 233 MHz, going perhaps as high as 266 MHz. Later in the year, Intel will phase in the 0.25-micron CMOS process. This will lead to a P6-class chip (code-named Deschutes) that should hit 300 or 333 MHz.
That'll be great for new buyers, but where does it leave the early adopters of the Pentium Pro? If Intel, as expected, discards the multichip module, Klamath almost certainly won't be compatible with existing 387-pin Pentium Pro sockets. Moving the L2 cache outside the package onto an external 64-bit bus would require 72 more pins. The only alternative would be to interface the L2 cache to the front-side I/O bus, but that would seriously impair performance.
The bottom line: If Intel segregates the L2 cache, existing Pentium Pro systems probably won't be upgradable to Klamath. The new chip wouldn't fit the old sockets, and the old motherboards don't have a daughtercard slot. Intel has long-rang
e plans for Pentium Pro OverDrive chips, but they probably won't appear before 1998. Pentium Pro users will end up swapping motherboards or buying a whole new system.
On the bright side, those new motherboards and systems will cost less. New system chip sets from Intel and Silicon Integrated Systems (SiS) are slashing the cost of building a Pentium Pro system. For example, Intel's new 440FX chip set has only three parts and costs less than half as much ($94) as the eight-part 450KX chip set found on many of today's Pentium Pro motherboards. And SiS offers a one-chip solution, called Archer, that costs only about half as much ($39) as the 440FX. Moreover, these solutions work with four-layer motherboards instea of the six-layer boards required by the 450KX. Although they sacrifice a few features -- such as memory expandability and multiprocessor support -- these compromises are reasonable for desktop systems priced in the $2000-to-$3000 range.
Merced Mania
Further out is Intel's se
venth-generation x86, the mysterious P7/Merced. Merced will extend the 32-bit x86 architecture to 64 bits and introduce a new instruction set. This architecture, dubbed IA-64, will be backward compatible with the existing x86 architecture, just as the 32-bit architecture of the 386 was compatible with the 16-bit 286, 8086, and 8088.
Although Merced is the fruit of Intel's partnership with Hewlett-Packard, it's looking less likely that IA-64 will radically depart from today's x86 architecture by adopting very-long-instruction-word (VLIW) technology. Intel will probably take a more conservative approach by extending the microarchitecture of the Pentium Pro. Pure VLIW is the antithesis of Intel's current design track; the Pentium Pro optimizes the instruction stream during execution, while a true VLIW processor would shift that responsibility to the compiler at design time.
There's still plenty of performance to be gained by extending the Pentium Pro's "dynamic execution" core. Intel could expand the reo
rder buffer, tweak the reordering algorithms, improve the branch prediction, add more execution units, boost the Level 1 (L1) caches (which are relatively small), and make other general improvements that would legitimately represent a seventh-generation design.
If VLIW plays any role at all, perhaps Intel and HP have found a way to adapt some tenets of that philosophy to the x86, just as Intel has integrated some elements of RISC into the Pentium Pro. Or maybe a full-blown VLIW design will appear in a subsequent processor.
Intel's alliance with HP also calls for Merced to run PA-RISC software. Some observers think this trick will require emulation, in either software or hardware. It would be useful to run PC applications on an HP workstation, but it's doubtful that the ability to run PA-RISC software on PCs would win significant additional market share for Intel.
In any event, Intel is committed to a 64-bit CPU that runs 16- and 32-bit x86 software without emulation. Native IA-64 programs will run
faster than 16- or 32-bit programs, but nobody -- possibly not even Intel -- knows exactly how much faster.
Another unknown is how quickly the industry will adopt IA-64. Remember, it's been 11 years since Intel went 32-bit with the 386 in 1985, and most PC users are only now migrating to 32 bits. Microsoft didn't ship a 32-bit OS until 1993, and the vast majority of PC users still use 16-bit Windows 3.1 or 16-/32-bit Win 95. Although Microsoft recently dropped some vague hints about a 64-bit Windows NT, the first 64-bit OS for Merced will probably be Summit 3D, a new flavor of Unix currently under development by HP and The Santa Cruz Operation (SCO). If the 64-bit transition follows the same course as the 32-bit transition, then IA-64 won't be a significant market force until the year 2009.
Cyrix Crystal Ball
After a shaky start with the 6x86, Cyrix is finally gaining on Intel's price/performance lead. The first 0.6-micron version of the 6x86 suffered from a huge die. Cyrix swit
ched to a process with five layers of metal instead of three, shrinking the die from 394 square millimeters to 210 mm². During the summer, Cyrix moved to a 0.5-micron process, achieving a die size of 170 mm².
Like an overweight athlete shedding excess fat, the 6x86 chip now runs a lot faster: 150 MHz instead of 100 MHz. And thanks to a more efficient microarchitecture, the 6x86 easily outruns a Pentium at the same clock speed. In fact, the 150-MHz 6x86 chip slightly outperforms a 200-MHz Pentium, which is why Cyrix designates this chip the 6x86-P200+ in accordance with the P-rating benchmark (see the sidebar "The Problem with P-Ratings").
Recently, however, BYTE discovered that some 6x86-based systems have a serious problem with the final-release candidate of Windows NT Workstation 4.0. We ran 32-bit Windows applications tests on a 6x86-P200+ system and then compared the results to those obtained on the same system with a beta version of NT 4.0. To our surprise, the tests ran about 25 percen
t slower on the release candidate of NT 4.0. The 6x86 also ran NT 4.0 about 16 percent slower than NT 3.51 and 24 percent slower than Win 95. In similar tests with Pentium-based PCs, performance improved on the release candidate of NT 4.0.
This problem might be related to some last-minute code that Microsoft added to NT to make it more stable on Cyrix-based PCs. Check The BYTE Site (
http://www.byte.com
) for the latest updates on this developing story.
The x86 Gets Faster with Age
