Intel's 875P chipset and P4 3GHz processor

By: Scott Wasson

THE CHIPSET code-named Canterwood has been spoken about in hushed tones,
in the right circles, since its existence was first rumored on a leaked roadmap
or internal document somewhere. Core-logic chipsets may not seem too sexy to
the wider world, but we hardware geeks know better. The rumored specs on this
thing sounded amazing, and what's more, Intel was planning to offer products
targeted for PC enthusiasts bent on wringing the best possible performance out
of their PCs. Not only that, but Canterwood would be Intel's first chance to counter
AMD's upcoming processor platform, Athlon 64.

As you know, AMD's Athlon 64 didn't quite make it out the door. It's pushed back
until this fall while AMD works out some manufacturing snags. But Intel appears
to be right on schedule. Just over a week ago, a Canterwood sample platform
arrived at Damage Labs, ready for testing. Naturally, we rounded up every
competitor we could and put Canterwood through its paces. We've also thrown
in AMD's latest and greatest, the Athlon XP 3000+, to see how it measures up
to Intel's latest. Read on to see what we found.

Our 875P test platform has a large passive heat sink on the MCH chip

Introducing the 875P chipset
Now that it's hitting the market, Canterwood gets a "real"
name: the Intel 875P chipset. The 875P is the first of a new wave
of chipsets coming from Intel, most of which are currently nestled
under the code name Springdale. The 875P brings a whole range of
enhancements to the Pentium 4 platform, so I'd better bust out
the bullet points to be sure I cover them all. They are...

• An 800MHz front-side bus — The 875P, in conjunction with
Intel's new Pentium 4 3.0GHz chip, can run its front-side bus at
a clock speed of 800MHz, or, more specificially, a quad-pumped 200MHz.
All of the 875P's predecessors and current competitors max out
at 533MHz, which gives them 4.2GB/s of peak bandwidth, in theory.
The 875P's peak theoretical bus bandwidth is 6.4GB/s.

Intel's new 800MHz bus-ready Pentium 4 3.0GHz processor

• Dual channels of DDR400 memory — To match up with its nosebleed-inducing bus speed, Intel has given the 875P two channels of DDR400 memory. Working in concert, these memory channels can deliver up to 6.4GB/s of bandwidth, just like the 875P's 800MHz bus. Also, the 875P will support ECC memory

Dual Kingmax DDR400 DIMMs populate the 875P-based Intel mobo

• PAT — No, it's not a confusion-inducing, omni-gendered character from Saturday Night Live; it's a marketing term masquerading as a three-letter acronym. PAT stands for Performance Acceleration Technology, which is an astoundingly vague name for what Intel is doing with the memory controller.

What Intel is doing, in fact, is "binning" its chips, just like it does its processors. Here's my best guess about what's happening. In all likelihood, the 875P silicon will come from the same wafers and essentially be the same chips as Intel's upcoming Springdale chipset, but Springdale will be a cheaper, higher-volume product. (Springdale chipsets will differ from the 875P only in that they won't include PAT or support for ECC memory types.) The 875P will cost a little more, and will be aimed at workstation users and enthusiasts. Intel probably plans to pick the very fastest Canterwood/Springdale MCH (north bridge) chips and test them to verify they're capable of running with PAT enabled. The best of those chips will be sold as 875P MCH chips.

With PAT enabled, the 875P memory controller will perform some internal memory handling tasks faster, yielding a one-clock improvement in the time for a CPU request to perform memory access and another one-clock improvement in the DRAM chip select process. The total improvement—count with me here—is two clocks for each chip select (CS) process. CS happens at the beginning of a typical memory access, so cutting the CS process by two cycles could lead to real-world reductions in memory access latency.

(It's as if Intel were gearing up to fight a processor with an on-chip memory controller or something, innit?)
Intel emphasizes that 875P chipsets are tested rigorously, at full operating speed, for their ability to run with PAT enabled, so Canterwood motherboards ought to be plenty stable under normal operating conditions. Intel is also quick to point out that PAT happens internally in the memory controller, while external memory interfaces run according to their specifications.

A block diagram of the 875P chipset — Source: Intel

• AGP 8X — The 875P chipset supports AGP 8X, which offers 2.1GB/s of dedicated bandwidth for a graphics card. The current Intel mainstream chipset, 845PE, only offers AGP 4X, so this is an improvement.

• Hyper-Threading support — Ok, this isn't exactly new, but the 875P supports CPUs with Hyper-Threading, as do most Intel chipsets. You can read more about Hyper-Threading in our review of the first HT-capable processor.

• Serial ATA with RAID — The 875P's ICH5 chip is the first PC "south bridge" chip with built-in support for the new Serial ATA drive interface standard. The ICH5 includes two channels of Serial ATA 150, which works out to two ports for two devices, because Serial ATA offers a dedicated connection per channel. To learn more about Serial ATA, let me suggest our excellent comparison of Serial ATA and "parallel" ATA drives.

To underline the point that Canterwood is targeting us PC enthusiasts, Intel is making a special version of the ICH5 chip, the ICH5R, with Serial ATA RAID capability. Near as I can tell, this Intel test board will only support RAID 0, or striping, for increased performance. Intel's literature doesn't talk about the possibility of using RAID 1, which would be my preferred config. But then I'm an old fogey. You can read up on all the common RAID levels and their benefits in Diss's impressive ATA RAID round-up.

• Communications Streaming Architecture — Everybody knows the PCI bus is straining to keep up with today's high-speed devices, and most core-logic chipset designers have opted to incorporate more and more high-speed I/O interfaces on their chipsets' south bridge chips. Intel has taken that trend one step farther by incorporating a communications interface right on its MCH chip, where a Gigabit Ethernet chip (like Intel's own, for instance) can access memory without the latency associated with the MCH-ICH chip-to-chip interconnect or—heaven forbid—the PCI bus.

• Accelerated Hub Architecture — Oddly, Intel hasn't elected to update its Accelerated Hub Architecture to provide more bandwidth between the MCH and ICH chips. The ICH5 chip offers two Serial ATA 150 channels, two ATA/100 channels, and a PCI bus (that's 633MB/s of bandwidth right there), plus four USB 2.0 controllers and more, Intel's interconnect maxes out at 266MB/s. No wonder they cooked up the Communications Streaming Architecture for Gigabit Ethernet.

This decision is kind of curious. Intel's competitors have north-to-south bridge interconnects capable of anywhere from 533MB/s to 1GB/s, but the mighty Canterwood may strain under heavy I/O loads.

Taken together, these new features add up to a much more potent Pentium 4 platform, especially because of the extra bandwidth afforded by the new front-side bus, dual memory channels, and the AGP bus. The P4 has long excelled at streaming media and I/O tasks, and the 875P looks to throw that trend into overdrive.