Clash of the Titans: Next-Generation Desktop CPUs

This fall's biggest battle won't be movie theaters' Freddy vs. Jason -- it'll be Intel's Pentium 4 successor 'Prescott,' the ultimate 32-bit PC processor, versus AMD's Athlon XP replacement, the pioneering 64-bit Athlon 64. Vince Freeman offers an updated preview of the desktop duel and which technical and marketing issues will be critical for both CPUs.
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Athlon 64 and Prescott Get Ready To Rumble

After a busy spring, desktop PC processor buffs have nothing to watch but summer reruns -- Intel's Pentium 4 and AMD's Athlon XP received speed bumps and faster front-side buses in April and May, respectively, but things have been pretty quiet since. That's going to change in a big way, however, as both firms launch truly new CPUs this fall. Here's an updated preview of what to expect -- and how the archrivals' offerings show very different views about where the desktop market will be in late 2003 and early 2004.

Opterons for Everyone: AMD's Athlon 64

Sometime this autumn -- the latest guesses point to the second half of September -- AMD will take a quantum leap from its venerable K7/Athlon/Socket A architecture, and traditional follow-the-Intel role, with the introduction of the Athlon 64. The desktop sibling of the Opteron server and workstation CPU introduced last April, the Athlon 64 represents AMD's bold bid to move mainstream computing from 32- to 64-bit technology, without leaving existing 32-bit Windows software behind.

Like the Opteron, the Athlon 64 offers a colossal increase in memory-addressing headroom compared to the 4GB limit of 32-bit processors; the chip can handle up to a terabyte of physical memory (using 40-bit addressing) or 256 terabytes of virtual memory (using 48-bit addressing).

While PCs with more than 1GB of RAM are still scarce today, AMD is betting that cinematic-quality 3D games and other applications will be bumping up against the 4GB ceiling on the desktop -- as enterprise databases and simulations are already doing on the server -- before we know it.

Meanwhile, to meet the never-ending demand for faster performance, AMD has made several improvements -- such as a longer pipeline, improved branch prediction, larger look-aside buffers, and support for SSE2 multimedia instructions -- to insure the Athlon 64 will outrun an Athlon XP at the same clock speed.

The most important piece of the Athlon 64 performance puzzle is the CPU's integrated memory controller, which allows extremely low-latency accesses to DDR memory -- while Intel's latest Pentium 4 raised the speed limit of the front-side bus from 533MHz to 800MHz, AMD has eliminated the front-side bus altogether.

This requires a new way of looking at memory and CPU bandwidth requirements, as the chipset and system bus speed have been taken out of the equation. It also brings up the option of boosting memory performance through a CPU design change, and AMD may be considering this path already -- while the initial Athlon 64s will incorporate a single-channel memory controller, AMD may be readying a dual-channel design for 2004.

Using its 0.13-micron SOI (silicon on insulator) fabrication process, AMD has found room on the Athlon 64 die for a hefty 1MB of Level 2 cache. This is an important design win, since Intel will move to a 90-nanometer process before reaching the 1MB mark for its desktop line.

AMD has decided to identify different Athlon 64 chips with model numbers indicating overall performance, akin to the Athlon XP's, rather than the generic Model 240/242/244 scheme of the Opteron. In clock-for-clock performance comparisons, the enhanced core, larger cache, and 64-bit architecture should all help the new CPU outrun its competition.

The only potential issue is that the Athlon 64 will ship at significantly lower clock speeds than its Intel rivals or even than the Athlon XP: The lowest-speed model at release, the Athlon 64 2800+, runs at 1.6GHz (like the Opteron 142 and 242), while the Athlon XP 2800+ has a core speed of 2.08GHz.

This disparity in clock speeds brings its own set of challenges. Many benchmarks demonstrate overall system performance, while others concentrate on video- or CPU-specific functions. Excelling in all of these areas is key to winning the benchmark race, and a 1.6GHz processor is going to be hard-pressed to match a 3.2GHz or higher competitor in pure CPU tasks. However, AMD's prospects should get steadily better, as Athlon 64 3100+, 3400+, and 3700+ models are all scheduled for 2003 release, with a 4000+ to follow early in 2004.

A Duron 64?

All of the above refers to the primary, top-of-the-desktop-market Athlon 64, but AMD is reportedly readying a lower-cost model -- sort of an AMD64 equivalent of its old Duron CPU -- to replace the Athlon XP as an affordable mainstream offering. This Athlon 64 "Paris" will feature only 256MB of Level 2 cache, and could duplicate the Socket A Duron and Athlon families' same-pinout approach, much beloved of system upgraders and IT managers, for the 64-bit generation.

In the meantime, it might get a little crowded with all the AMD desktop CPUs to choose from -- not only two different Athlon 64s, but multiple bus-speed variations of the Athlon XP "Barton" and older "Thoroughbred," or perhaps the rumored "Thorton" (the up-to-date Barton core with a Thoroughbred-level 256K instead of 512K of L2 cache). AMD even still has a couple of Duron models in production.

Though the Athlon 64, like the Opteron, is built to be blazing fast with existing 32-bit operating systems and applications, software support will be a critical factor in the new CPUs' success. While Microsoft has pledged to join today's handful of Opteron Linux distributions with 64-bit versions of Windows XP and Windows 2003, time is growing short: the Opteron is already in the channel, and for the Athlon 64 to make a big splash in the 2003 holiday-season buying market, AMD64 Windows XP must be ready upon launch.


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