P55: The Chipset’s Responsibilities Dwindle

Say farewell to Intel’s conventional three-component platform design. P55 (and very likely every desktop chipset moving forward) centers on a two-chip implementation consisting of the CPU and one piece of motherboard core logic. Surely, there’s a team of Nvidia engineers feeling pretty gosh-darned vindicated right now.  

With the memory and PCI Express controllers now part of Lynnfield (and graphics migrating that direction with Q1’s Clarkdale launch), there’s little else for a chipset to do except the functionality formerly handled by Intel’s ICH southbridge lineup. Thus, P55 gives you six 3 Gb/s SATA ports, a Gigabit Ethernet MAC, 14 USB 2.0 ports, HD Audio, and eight lanes of PCI Express 2.0 for peripheral connectivity. As an indication of how far southbridge technology has come in the last two years or so, P55 is wholly uninspiring.

There is some notable power savings here compared to X58, though. To begin, Lynnfield sports a 95W TDP. Bloomfield is 130W. The X58 Express IOH is a 22W part. That vanishes completely. P55 uses up to 4.7W. And ICH10R consumes up to 4.5W. Add it all up and you’re down more than 56W right off the bat.

Making The Connection

Intel’s most recent three-chip desktop platform, X58, employed a 25.6 GB/s QPI link between the Core i7 CPU and X58 IOH. It then used a 2 GB/s DMI connection between X58 and the ICH10 chipset component.

As we shift to P55 and its two-chip design, the northbridge gets absorbed into Core i5/Core i7, and we’re left with what amounts to a southbridge attached to the processor, even if Intel refers to this as a platform controller hub. As with the ICHes before it, P55 connects to its host (Lynnfield) through a DMI connection.

According to Intel, the DMI link between Lynnfield and P55 runs at 2 GB/s, similar to past-generation ICHes. Previously, that connection handled six lanes of PCI Express 1.1, SATA, USB 2.0, Gigabit Ethernet, and HD Audio. With the move to P55, most of those subsystems remain unchanged. However, the chipset now supports eight lanes of PCI Express 2.0.

Intel is nevertheless confident that its DMI link won't be saturated. The math doesn't lie, though. With the right combination of add-in storage and SSDs, it wouldn't be difficult to jam things up there.