Lenovo on Wednesday introduced its smallest, quietest, and most energy efficient desktop in the company's history.

The ThinkCentre A61e, a desktop the size of a telephone book, contains 45-watt AMD Athlon 64 X2 and Sempron energy efficient processors and costs as low as $399.

Lenovo claims the ThinkCentre A61e is the first full-functioning PC in the industry to use only 45 watts of energy. It can help reduce annual energy costs by 35%, the computer maker said.

As an example, a business with 50,000 desktops could save over $1 million in annual energy costs and cut more than 20 million pounds of carbon dioxide emissions.

Also codenamed "Blue Sky" for being environment-friendly, Lenovo's new desktop was given Electronic Product Environmental Assessment Tool (EPEAT) Gold status by the Green Electronics Council. The ThinkCentre A61e contains up to 90% of reusable and recyclable materials and 90% recyclable packaging. Additionally, a solar panel can power the desktop.

The ThinkCentre A61e complements another recent introduction by Lenovo of the ThinkCentre A61 desktop, which comes with features like an I/O port disablement for security and support for up to four monitors.

ThinkCentre A61e and A61 desktops will be available for sale next month.

Lenovo said it's responding to rising energy prices, which businesses are currently facing as they deploy computing devices.

Lenovo must respond quickly to such needs as it faces competition from other computer makers like Acer, which plans to acquire Gateway in December. If the deal goes through, Acer will become the third-largest computer maker in the United States after Hewlett-Packard and Dell, pushing Lenovo to the No. 4 spot.