That's the idea behind AMD's Athlon II X2 240e. It's a 2.8GHz dual-core processor based on the AMD "Regor" core with a TDP of just 45W. The "e" behind the Athlon II X2 240e model name indicates that it's one of AMDs Energy Efficient processors.

The Athlon II X2 240e also supports full hardware virtualization, allowing one of its two cores to run a copy of Windows XP inside of Microsoft Windows 7. Virtualized Windows XP will be especially practical when it comes to legacy software applications that don't run in Windows 7. The Athlon II is also the first CPU to move C1E low power states out of the BIOS and onto the CPU.

AMD's Athlon II X2 240e is aimed at both mainstream buyers and value-oriented PC applications where a lightweight, low-cost computer system is needed to fill the void. The processor costs $80 CDN ($77 USD, £50 GBP), which means its closest competition is AMD's own Athlon II X2 250. Let's find out if the Athlon II X2 240e can walk the tightrope between power consumption and performance...

AMD "Regor" core

If you've read PCSTATS' review of the AMD Athlon II X2 250, you should already be familiar with AMD's "Regor" die. Regor is AMD's mainstream CPU die. . To make sense of AMD's Athlon II X2 240e processor, it's good to get the big picture of AMD's current CPU offerings first. AMD currently has four different families of 45nm desktop processors that make up its Phenom and Athlon brands.

The fastest and most expensive of these is the AMD Phenom II X4, based on the "Deneb" die. This is what you'll find running under the hood (or under the heat shield, to be specific) of processors like the Phenom II X4 965 Black Edition, AMD's current flagship processor. It has four cores and 6MB of L3 cache.

Slotting in underneath "Deneb" are AMD's enthusiast dual-core dies, codenamed "Callisto". This die has two cores but still keeps the 6MB of L3 cache, which makes it a very good candidate for overclocking performance. You can find "Callisto" dies in the AMD Phenom II X2 550 Black Edition. On the Athlon side of things, there's the quad-core "Propus" die. This processor die is actually very similar to "Deneb", with the same four cores but missing the L3 cache. AMD has turned "Propus" into its mainstream quad and triple-core processors. Check out PCSTATS' review of the AMD Athlon II X4 620 processor for more information on the "Propus" die.

Which brings us to "Regor", the smallest and least complicated of the four 45nm AMD processor dies currently in circulation. "Regor" is what drives AMD's mainstream dual core processors, like the Athlon II X2 250 or the energy efficient Athlon II X2 240e. It has a pair of CPU cores, and no L3 cache.

The Athlon II X2 240e processor has a small die measuring just 117mm2 with a 234 million transistor count. Small sizes and low transistor counts are great when it comes to building energy efficient processors, and this is wheres Athlon II X2 240e-based PC can really shine. While some of AMD's "Deneb" processors (like the Phenom II X4 965 Black Edition) have TDPs in the 140W range, AMD's standard "Regor" CPUs are rated at just 65W TDP.

And now, thanks to a bit of engineering magic, AMD has managed to make the Athlon II X2 240e even more energy-friendly bringing its maximum TDP to a mere 45W. That's less than a light bulb.

Low wattage processors aren't always the most exciting when it comes to high clock speeds, number-crunching or multi-threading, but they do have a lot of practical uses, particularly when it comes to building a secondary PC that's only doing a limited number of tasks.

Take building a home media PC that doubles as a media server, for instance. It's a PC that will likely be on all the time in order to serve media to a home network, so it's ideal for a processor like the Athlon II X2 240e which doesn't use a lot of electricity.