Green winds of change are blowing through the world of PC design, and Zonbu's flash-based, diskless and non-Windows ultra small box reflects them. While Windows Vista has advanced power management, leading to energy savings, it cannot match the claimed power-savings of Zonbu's desktop.

The traditional idea of a Windows PC on every desktop and in every home is coming under pressure as people realise that distributed computing resources are expensive, power-hungry and inefficient. There is a strong move to concentrate physical computing resources in data centres with IBM's announced mainframe upgrade of its data centres typical of this.

Virtual servers and virtualised file and block storage are also part of this resource concentration in the data centre, with networked access by desktop PC users.

Zonbu has taken this concentration concept a step further and developed a thin-client style PC with a chassis the size of a paperback book. It is diskless and stores files on Amazon's S3 simple storage service facility.

The device uses a 1.2GHz VIA x86 chip, and has 512MB RAM and 4GB flash-based local storage, from which the OS and applications are started. There are hardware graphics and MPEG2 acceleration, keyboard and mouse ports, six USB ports and 10/100 Thernet support is built-in. There are no fans, and indeed there are no moving parts at all. This means the unit is completely silent.

The operating system is Linux and it comes with 20 pre-loaded applications, including a browser, email, calendar, full office document tools, finance, video playback, Skype, instant messaging and publishing. There is a transparent GUI, similar to Windows' Aero or the Mac OS Tiger Aqua.

It costs $99 (£50.00 at standard conversion rates) if you buy two years of Amazon's S3 service, and will be available in September.

The Zonbu device consumes only about one third of the energy used by a typical light bulb and carbon offset purchases are claimed to make it carbon-neutral. A single incandescent 100-watt light bulb left on around the clock for a year costs more than $80 to power. Generating that power releases about 1,350 pounds of carbon dioxide emissions into the atmosphere, which contributes to global warming.

Dean DeWhitt, director of Microsoft’s Windows Kernel team, says that is about the same amount of power many PCs consume while not in use.

Traditional PCs run a disk-intensive operating system, Windows, the latest version of which requires more memory and disk, and faster processors, to run than before. Windows Vista has been criticised for its lack of green credentials.

The chief executive of Computer Aid International, Tony Roberts, argued earlier this year that Vista's hardware requirements would lead to millions of old PCs being replaced, and said: ""If you imagine each of these 10 million machines contains lead and many other toxic chemicals then we really are storing up an environmental disaster."

Derek Wall of the Green Party said: "Vista requires more expensive and energy-hungry hardware, passing the cost on to consumers and the environment."

Microsoft has responded to these criticisms by commissioning a report showing that Windows Vista could run well on 3-year old hardware, meaning no mass PC replacement programme, and isn't a power-using hog. That's because it has much better power-saving features when the PC is not being used. A Vista PC could use less energy in a year than a Windows XP desktop because of this.

DeWhitt said: “Ultimately, PC users will decide how much of a difference power management can make. What we’re trying to do at Microsoft is give people a way to use personal computers that delivers a great user experience and is also a very efficient way to use personal computers. The energy savings associated with these efficiencies, scaled over millions of PC users, can really add up.”

If a PC is switched off when not in use, then these power-saving features are moot. Also, as a Vista PC uses spinning disks it cannot approach the energy savings of a diskless PC like the Zonbu. Flash memory is becoming more affordable and such diskless PC design ideas, with OS and applications stored in flash memory, may well become more common.