When DC Comics introduced the Atom in 1961, the comic-book star was dubbed "The World's Smallest Superhero" for his battles with villains many times his size (and with Marvel Comics' Ant-Man -- Ed.) The tradition continues today with the Intel Atom, a new processor that uses its diminutive size and low power consumption to compete against larger, more powerful CPUs. This is quite a shift in strategy for Intel, as the company has long touted clock speed and overall performance as ways to hammer its mobile and desktop competitors.

Maximum Tech for Minimum Power

The Atom processor announced in March is based on existing x86 technology, but its internal microarchitecture is different from that of the Pentium and Core 2 lines. When designing a new processor core for the Atom, the company focused not on a performance goal but on trimming power and thermal requirements while keeping costs low and chip yields high.

Intel uses its hafnium-based 45-nanometer-process Hi-k metal gate silicon technology for the Atom CPU, allowing the line to pack 47 million transistors into a die size only 25 millimeters square. There's 56K of Level 1 cache -- 24K for data and 32K for instructions -- plus an on-die 512K, 8-way Level 2 cache with dynamic cache sizing.

The official front-side bus support is 533MHz, though a couple of ultra-low-power models use a 400MHz bus. Other features include support for SSE2/SSE3 multimedia instructions, Execute Disable Bit, and Intel's SpeedStep power consumption adjuster.

In a world dominated by dual- and quad-core processors, the Atom is a single-core model that lacks any true speculative hardware. Instead, it uses an old-school, in-order processing model with a single-channel memory architecture. This slows the CPU down, but permits a much smaller core and significant drop in power and thermal specifications.

For example, the 1.6GHz Atom Z530 has a thermal design power (TDP) of just 2 watts and a core footprint (182 mm²) less than 15 percent of that of a Celeron M ULV. This also means the Atom can be cooled passively, providing additional system power savings.

Rather than write off performance altogether, though, Intel added a very interesting feature to the Atom by adopting a form of the Hyper-Threading Technology introduced in 2002. This lets the Atom, like the old Pentium 4, handle two application threads at the same time, dynamically allocating physical resources between two logical processors. As we know from its heyday, Hyper-Threading doesn't offer the same performance boost as a true multicore design, but it does provide smoother multitasking and multithreading than a monocore without it.

Intel has always admitted that adding Hyper-Threading to a processor increases its complexity and power usage, which would seem to make it a strange choice for the battery-thrifty Atom. Then again, with a TDP of only two to four watts, the Atom is such a miser that adding HT has virtually no impact on the bottom line.

Looking at the lineup, all five 533MHz-bus Atom processors support Hyper-Threading, with only the 400MHz-bus parts -- the 1.1GHz Atom Z510 and 800MHz Atom Z500 -- lacking it. The Z500, by the way, is the miser of misers, with a TDP of a ridiculous 0.65 watt.

Splitting the Atom

The seven Atoms fall into three different subgroups, each targeted at a specific market segment. The five chips in the Z5 series are designed for pocketable Mobile Internet Devices or MIDs, to use Intel's phrase. The N270 is meant for the growing class of low-priced, stripped-down subnotebooks known as netbooks. The Atom 230 is an embedded solution for ITX-based small-form-factor systems dubbed nettops (the desktop equivalent of netbooks).

The multiple product names aren't just for show. For example, the Atom Z530, N270, and 230 all run at 1.6GHz with the same L1 and L2 cache and 533MHz front-side bus, but their power usage differs according to their target products' battery sizes (or the likely use of AC power for nettops).

The MID-ready model Z530 has a TDP of 2.2 watts, while the netbook-oriented Atom N270 draws 2.5 watts and the model 230 is the highest at 4 watts. Combine any of these with a low-power Intel 945GSE chipset with integrated graphics (4 watts), and the Atom enables an incredibly low total-platform TDP.

The Atom in Action

With few mobile Internet devices and nettops available yet (although home theater PC buffs are eyeing the Atom 230), Intel's newest CPU's main impact is being felt in the subnotebook market. The marketing strategy around the Atom processor matches perfectly with the netbook value proposition of an affordable, easy-to-carry alternative to a full-sized laptop for simple Web and e-mail access and personal productivity.

The $400 Asus Eee started this two-pound revolution last fall, but Intel wasn't ready to join up yet -- even using a low-power, underclocked Celeron M processor, Asus was obliged to go with a small 4GB solid-state disk (SSD) rather than a power-hungry hard drive for the 7-inch-screened subnotebook.

Now, several companies have adopted the Atom as their solution to building a smaller notebook. Asus' 8.9-inch Eee PC 901 and 10-inch Eee PC 1000 both have the Atom N270 under the hood. So do the 10-inch MSI Wind and the 8.9-inch Acer Aspire One -- and, reportedly, one or more netbooks coming soon from Dell.

The result is a quantum shift in the mini-laptop market, with Acer offering the Aspire One with a 120GB hard drive and Windows XP Home for $400. While both the OS and the hard disk may seem a little old-school in this era of Vista and SSDs, the Acer opens up the door to students and budget-strapped users, offering a truly functional and compatible platform at a size and price that is virtually unheard-of. (There's also a Linux/8GB SSD version with a likely street price as low as $350).

Of course, users should not expect blazing performance from a CPU created for modest mobile devices. The Atom is capable enough, but complaints have been levied against the MSI and Acer netbooks that response times are sluggish and overall performance falls short of expectations. The key to processors like the Atom is low power usage, and if you want a desktop replacement, look elsewhere.

There's no question that the netbook market is hot right now, and Intel's not the only company that stands to benefit. VIA has introduced the Nano, with performance considerably above that of the old VIA C-7 found in the HP 2133 subnotebook, and word is that AMD is preparing a challenger as well. The latter's integration of the memory controller and Northbridge functions into the CPU sounds great for a battery-friendly netbook, but, like VIA, AMD will face questions surrounding its platform base and likely industry adoption rates. When Intel helps develop a market, it tends to hang onto it.