The first of the recent generation of 64-bit processors debuted when Intel introduced the Itanium (which has since gone out of production) in June 2001. It followed up a year later with the Itanium 2, which fixed most of the problems that the original Itanium had, and has gone through many revisions since then. Both use Intel's IA64 instruction set architecture. Since IA64 was not based on the IA32 (x86) ISA, the new instruction set would enable Intel to maintain control over it -- competitors such as AMD would not be able to use it without a license.
While the Itanium was a great idea, it was poorly implemented -- comparably clocked x86 processors of the era performed as well as or better than the Itanium. The Itanium 2, however, still dominates SPEC's list of most efficient processors.
AMD introduced its AMD64 architecture in September 2003. Processors thus far include the Athlon 64 for desktop systems; the Athlon 64 FX on the high end of the single-CPU market; and the Opteron for high-end workstations and servers. All of them can run 32-bit and 64-bit binaries at the same time with no significant loss in performance.
Intel rushed to match AMD's success with the AMD64-compatible EM64T architecture, which is currently being sold in the newer Pentium 4 processors; the Pentium 4 Extreme Edition for single-CPU performance enthusiasts; and the Xeon and Xeon MP processors for high-end workstations and servers. The Itanium was originally expected to replace the first-generation Xeons, but poor market acceptance and substandard performance of the Itanium kept Xeon alive. The Xeon is Intel's flagship workstation and server processor, with the Itanium 2 being its high-end server offering.
Both the AMD and Intel 64-bit processors (with the exception of the Itanium 2, which is designed to be integrated into systems sold by OEMs like SGI and Hewlett-Packard) are sold individually to consumers at affordable prices. You can buy an AMD64 or EM64T processor, a supported motherboard, and the rest of the components for a workstation and build it yourself inexpensively in comparison to other 64-bit architectures. The rest of the CPUs in this section are only available as part of complete integrated computer systems.
IBM's 64-bit POWER architecture is best known as the basis for the PowerPC processors at the heart of Apple's G5 workstations. IBM has its own implementation of the POWER instruction set, found in its IntelliStation POWER series of high-end workstations. POWER-based processors of various kinds are found in a wide variety of electronic devices outside of the personal computer market.
Sun Microsystems' SPARC architecture started out as 32-bit, and in that form it is sometimes referred to as SPARC32. In 1995 Sun introduced the UltraSPARC 64-bit processor, with the architecture usually referred to as SPARC64. The design has been licensed by other manufacturers such as Fujitsu, but Sun still dominates the UltraSPARC workstation world.
SGI bought MIPS, the developer of the first 64-bit workstation processor, in 1992. As a workstation microprocessor, MIPS CPUs are primarily sold in SGI machines, although SGI licenses the design to a variety of other manufacturers. SGI has long been considering switching its workstations from MIPS to Itanium 2. The Intel 64-bit processor performs better and has the backing of the world's largest chip maker.
Other 64-bit architectures are already dead, victims of a swiftly moving market. Digital Equipment Corp.'s Alpha was the fastest microprocessor in the world when it was released in 1992, and survived throughout the 1990s as DEC's heavy-duty workstation CPU. Eventually Compaq acquired DEC, then HP acquired Compaq. HP finally announced the last of the Alpha processor line last August, and plans to replace Alpha-based systems with Itanium 2s, as it is replacing its own PA-RISC chips.
You might wonder how well-accepted each of these architectures is in the field. So did we, but we couldn't find a market analyst who could tell us the percentage of currently installed workstations that use these 64-bit architectures.
Where other architectures struggle to achieve 32-bit and 64-bit binary compatibility without losing performance or inconveniencing developers and users, the perfect 32-bit binary compatibility of AMD64 and EM64T is a valuable advantage to businesses.
"From a development standpoint," said Michael Dortch, principal business analyst with the Robert Frances Group, "Successful new architectures, 64-bit and otherwise, allow maximum leverage of current skills and resources, while requiring minimal investment in new skills and resources. This is especially true for internal enterprise developers, and for the more resource-constrained among commercial developers."
Software availability, price, service, and quality of manufacture remain the most important considerations in the success of 64-bit systems, Dortch said. "Enterprises don't buy chips, or computers, or even computing, per se. They buy solutions to business problems, and the solutions that offer the best applicability to those problems with the best reliability and performance at the best price will win. It's up to the developers of 64-bit architectures to build around those technologies the 'ecosystems' of applications, partners, and support necessary to generate and promote such solutions. Otherwise, 64-bit architectures are just one more opportunity for geeks to talk with other geeks about geek stuff most business people neither understand nor care much about."
Dortch also said it's a telling sign that the volume leader in AMD Opteron-based server sales is Sun Microsystems, which used to rely solely on UltraSPARC processors for its high-end machines. "Other 64-bit architectures are largely perceived as being only marginally significant to enterprises, except within specific compute-intensive niches," he said. Those compute-intensive niches these days are filled more and more by the Itanium 2. So since powerful, inexpensive 64-bit machines are starting to take over the workstation market, the older, much more expensive architectures can no longer compete in terms of price or performance.
The exception, for the time being, is the vertical scalability of SPARC64. For tasks for which more than 8 CPUs are needed in a single system, UltraSPARC scales more efficiently than the Opteron or Xeon, neither of which is designed for systems larger than 8-way.
Along with its advantages for vertical scalability, SPARC64 also has some architectural disadvantages. Theo de Raadt of the OpenBSD project, who has dealt with problems relating to binary compatibility on many platforms, says, "SPARC64 in complete 64-bit mode is running big-endian 64-bit. Big-endian and little-endian errors cause problems all the time, and so do 32-bit vs. 64-bit issues. But when you combine 64-bit and big-endian you end up with the most finicky programming architecture. This causes bugs for us, which we then fix, and since it is code shared between lots of architectures, all the code improves."
One of the factors that affects the longevity of a hardware architecture is its software support. Free software tends to be ported to dead or dying architectures, giving them new life as well as freedom from old proprietary Unix variants. The NetBSD project is famous for its portability, fully supporting more than 50 hardware architectures. GNU/Linux is available on more than 20 different architectures, and OpenBSD on 16. All will run on SPARC32 and most SPARC64 systems, AMD64/EM64T, Alpha, PA-RISC, and various implementations of MIPS and PPC.
Free software operating systems make old 64-bit systems useful again. With the BSDs or GNU/Linux, you can achieve some level of desktop functionality, or make an old workstation into a small server. And you can often find amazingly inexpensive workstations on eBay to play with.
In the end, all this talk of architectures and 64-bit design wars is purely academic. 64-bit architectures will come and go as the market dictates. Only the cheapest, most reliable, best supported, and most powerful players will remain in the game. Michael Dortch noted this point especially well:
"From a user (or non-IT executive) standpoint, the best 64-bit architectures are invisible -- all users know and see are applications that run faster and are more available than they used to be. From an IT executive's perspective, the most successful 64-bit architectures are similarly transparent. They 'play well' with incumbent 32-bit and other environments, delivering enhancements to availability, performance, or other operational characteristics as and when those translate into demonstrable business value with minimal disruption. In other words, 'no fork lifts required.'"
Well, maybe you would need a forklift to get that pallet of old Alphastations out of storage so you can use GNU/Linux to cluster them into a new backup server. Someday maybe we won't be so concerned with what is inside our computer so much as what software is running on it and what it enables us to do.