Intel Corp. may be best known for its PC processors, but the company is also the largest motherboard chipset manufacturer in the world. The Intel chipset line caters to all levels of the market, from bargain-basement integrated-graphics, no-AGP-slot solutions like the 845GV all the way up to sophisticated workstation and server chipsets like the E7500 and E8800 series, along with a few decidedly high-end desktop platforms.

In the latter arena, features like dual-channel DDR memory controllers, AGP 8X, and Serial ATA storage support are becoming standard issue, with Intel once again at the forefront. The company actually started today's dual-channel desktop craze with the Intel 850 platform for the first, RDRAM-based Pentium 4 systems. (See "The Dual-Channel Revolution" and "Your PC's Second Most Important Silicon" for more on chipset architecture -- Ed.)

While the Pentium 4 stuck with RDRAM, vendors using its AMD rivals opted for DDR memory, and Nvidia's nForce chipsets made dual-channel DDR the high-performance formula in the Athlon XP arena. Later, when Intel returned to the DDR fold, it migrated from standard single-channel designs to the powerful E7205 workstation chipset -- and, in mid-April of this year, to the 875P "Canterwood" chipset for Pentium 4 desktops.

It should soon be joined by more affordable or mainstream 865-series (codenamed "Springdale") siblings, but the 875P is for now the top dog in the Intel desktop pack. Indeed, due to its combination of high-end performance and up-to-date features, Canterwood actually straddles the fine line between desktop and workstation platforms.

New Northbridge, New Bus

The 875P uses a conventional two-chip (Northbridge and Southbridge) solution to link the CPU to, respectively, primary pathways such as system memory and the AGP graphics bus, and less data-intensive peripherals such as disk drives and USB devices. The Northbridge shares a great many features of its E7205 counterpart, such as AGP 8X support and a dual-channel DDR controller.

The two big upgrades here were to add official support for the 800MHz front-side bus that debuted in the Pentium 4/3.0C processor and to step up DDR memory speeds to the 400MHz (DDR400 or PC3200) level. Given the similarities between the 875P and E7205 -- the latter of which can be run at higher than its rated 533MHz front-side bus and DDR266 memory speeds -- "official support" is the key phrase, and ensures that all manufacturers will offer a standard 800MHz-bus/dual-DDR400 configuration, in addition to adding a few wrinkles of their own.

System bus speeds are an important component of overall performance, and Intel has really been pushing ahead with faster front-side paths -- in fact, leapfrogging the anticipated 666MHz bus entirely -- and corresponding boosts in memory bandwidth. The 875P supports 400MHz-, 533MHz-, and 800MHz-bus Pentium 4 processors, with the last upgrading theoretical CPU bandwidth to an astonishing 6.4GB/sec -- a significant jump from the 4.2GB/sec of the 533MHz-bus models. According to Intel documentation, the 875P is even compatible with Intel's next-generation 90-nanometer "Prescott" core.

In short, this is looking like one future-proof chipset, with the only caveat being that the Pentium 4/3.0C is at this writing the only 800MHz-bus processor available, and it comes at a hefty premium over the 533MHz-bus 3.06GHz model.

Dual-Channel DDR400 Design

Naturally, an 800MHz CPU bus needs a high-end, high-speed memory architecture, otherwise it's just a lot of wasted potential. A synchronous memory bus is always the optimum choice, and by providing dual DDR400 support, Intel has done just that. The resulting 6.4GB/sec of memory bandwidth matches the CPU bandwidth perfectly, thus minimizing any potential timing issues between components.

When you hear the term dual-channel memory controller, it's natural to imagine two distinct memory pathways, each sending data back and forth from the CPU and other peripherals. This is the architecture of conventional dual-channel solutions like the nForce2, but Intel has taken a slightly different route to doubled memory bandwidth: Instead of two physical 64-bit DDR channels, the 875P (and E7205) create one 128-bit pathway, and allow data to be accessed in 128-bit chunks.

Neither method is inherently better than the other -- Intel's eliminates the need for an arbiter to distribute the load between channels, but requires more complex circuitry elsewhere in the chipset -- and both yield the same doubling of memory bandwidth.

One unique feature that debuts with the 875P, however, is what Intel calls Performance Acceleration Technology (PAT). According to the company, through "advanced manufacturing and testing", PAT lets the clock timings for each DRAM chip select be lowered by 2, thereby speeding data flow between the CPU and system memory for an extra ounce of performance.