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The Menlow basics
For those who are familiar with Intel's desktop-class products, the fundamentals of the Menlow platform will be comfortable territory in many ways. Still, both the Silverthorne processor—now Atom—and the Poulsbo chipset—now the System Controller Hub—are new-from-the-ground-up designs. Or, as many folks seem to be saying these days, "grounds-up" designs, which sounds like an exotic method for brewing coffee. (Note to self: Investigate.)

Silverthorne is a much different beast than Intel's current Core 2 desktop and mobile processors, with an entirely new microarchitecture designed to hit a much smaller power budget. Performance was an important, but secondary, consideration in this architecture's genesis. The chip itself packs "only" 47 million transistors into a die that's a dimunitive 7.8 by 3.1 mm, or just over 24 mm². Intel has used its most advanced 45nm high-k chip fabrication process to produce Silverthorne, the same process it uses for Core 2 "Penryn" chips. (By contrast, Penryn's die is 107 mm².) Even when mounted on a package for integration, Silverthorne will measure only 13 x 14 mm, with a height of 1.6mm.

The first Silverthorne processors will range in clock speed from 800MHz to 1.86GHz, and they will communicate with the rest of the system via Intel's familiar front-side bus, with bus clocks of either 400 or 533MHz, depending on the product. (In fact, since Silverthorne uses this bus protocol, it's theoretically compatible with Intel's current desktop and mobile chipsets.) Silverthorne-based chips all pack 512K of onboard L2 cache, and the design team waded deep into Intel's alphabet soup of technologies, building in compatibility for VT, XD, EM64T, SSE3, SSSE3, SpeedStep, and HT.

Phew, OK, let's unpack that a bit.

The notable acronyms include EM64T, which is Intel's name for x86-64 compatibility (so you could run Windows Vista x64 Edition on your next Garmin Nuvi, I suppose). SpeedStep is Intel's name for its dynamic power management technologies, of which Silverthorne has a full complement. And the most intriguing of all may be HT, for Hyper-Threading, Intel's rendition of simultaneous multithreading, a technology first (and last) implemented on the Pentium 4. Although Silverthorne is natively a single-core processor, certain models expose two threads to the operating system and execute them together in order to achieve higher performance.

We've already noted Silverthorne's approximate power budget. More specifically, TDP ratings range from 0.65W for the lowest end models to 2.4W for the fastest ones. And I've already mentioned that Silverthorne is a low-cost affair. Exactly how low may surprise you, though. Here's an overview of the various Silverthorne models and their pricing.

Model Clock speed FSB speed L2 cache Hyper-
Threading
TDP Average
power
Idle
power
Price
(CPU + chipset)
Z500 800MHz 400MHz 512K - 0.65W 160mW 80mW $45
Z510 1.1GHz 400MHz 512K - 2W 220mW 100mW $45
Z520 1.33GHz 533MHz 512K x 2W 220mW 100mW $65
Z530 1.6GHz 533MHz 512K x 2W 220mW 100mW $95
Z540 1.86GHz 533MHz 512K x 2.4W 220mW 100mW $160

Notice that the CPUs' TDP ratings are very much maximum values. Both the idle and estimated average power numbers for the processors are much lower, in the milliwatt range. This is the sort of territory Intel's design teams for Silverthorne and Poulsbo had to navigate when considering power consumption.

Silverthorne pricing includes a Poulsbo System Controller Hub. Poulsbo integrates several different chipset functions into a single chip: a north bridge with a FSB and memory controller, a south bridge with various sorts of I/O blocks, and a graphics processor. The north bridge's bus capabilities mirror Silverthorne's, with frequencies of either 400 or 533MHz, and the memory controller supports a single channel of DDR2 memory at the same 400/533MHz clock speeds. The south bridge is but a subset of a traditional PC's, with two PCIe x1 links, eight USB 2.0 ports, HD Audio, and—oddly enough—an ATA/100 disk interface. This one is, I believe, simply the result of Intel guessing wrong about the penetration of SATA into mobile drives when it created the Poulsbo spec. More presciently, the SCH can also talk to flash RAM via three SDIO/MMC ports.


The Poulsbo SCH die. Source: Intel.

The vast majority of the SCH, of course, is dedicated to the integrated graphics processor. Although it's a low-power component, this is truly a PC-class GPU, with OpenGL and DirectX 9 support (under Windows Vista, at least) and what Intel calls "full" HD video decode acceleration. This IGP comes with a big surprise and a mystery attached, though. The surprise is that Intel has gone to a third-party provider for this low-power GPU, and the big mystery is the identity of that supplier. Could it be Nvidia? ATI? Poulsbo has been in development for three years, so nearly anything seems possible. AMD hadn't yet snatched up ATI when development started, and the impending Larrabee project hadn't yet alienated Nvidia. Intel wouldn't tell us who was providing the SCH's graphics core, but I expect to find out in the next few days as the Menlow platform's details become public. (Update: Turns out the GPU maker is Imagination Technologies, the PowerVR guys.)

The SCH is a somewhat larger chip than Silverthorne, partly because it's manufactured using an older 130nm fab process. Intel says it chose 130nm because low-leakage circuits were readily available on that process. Also, the SCH's physical size is limited by the large number of I/O pads it requires.