In summer 2001, Intel and Microsoft jointly rolled out the first-generation Itanium (formerly code-named Merced) hardware—Intel's first 64-bit computing platform—and prerelease versions of Windows XP and Windows .NET Server (Win.NET Server) designed specifically for 64-bit platforms. However, the Itanium—which sidestepped backward compatibility with existing x86 products and offered mediocre performance—bombed in the market, selling barely several thousand total units. Intel now has a new Itanium family member that might solve those problems, but a 64-bit AMD challenger is also on the way. Here's what you need to know about 64-bit computing.

Intel's Itanium Family
Reacting to criticism of its first-generation Itanium, Intel's Itanium 2 offers up to twice the performance of its predecessor. Interestingly, the Itanium 2 doesn't perform this feat through sheer megahertz (the Itanium 2 debuts at just 1GHz, on;y a slight improvement over the original Itanium's 733MHz and 800MHz speeds) but rather through on-chip performance tweaks and 3MB of L3 cache. The Itanium 2 doesn't address the biggest problem with Intel's 64-bit architecture, however, because it must emulate 32-bit Windows to run today's applications—and it runs them slowly.

AMD Opteron
Upstart chipmaker AMD has often existed in Intel's shadow, and for years, AMD fed off the low end of the market. But when Intel targeted the low-end market with its Celeron line, AMD went upscale—first with its AMD Athlon line of high-performance CPUs, then with its new AMD Opteron family of 64-bit processors, due out later this year. AMD's approach to 64-bit computing just might spell success: The AMD Opteron is fully backward-compatible with today's x86 line of processors and that platform's many applications. Microsoft has pledged to fully support the AMD Opteron in future Windows versions, giving Microsoft a viable 64-bit platform to fall back on if the Itanium tanks.

Recommendations
Sixty-four-bit computing isn't about raw performance, but about overcoming the limitations of today's 32-bit architectures. Thus, 64-bit computing means support for more memory, more expansion headroom, and more scalability.

But in reality, you probably don't need 64-bit computing yet. If you want the ultimate in scalability, check out the 32-way x86-based servers that Unisys and other companies offer. These systems run Win.NET Datacenter Server (formerly Windows 2000 Advanced Server) and rival the highest-end UNIX servers. Best of all, these systems are compatible with all of today's important server software.