"In the end you've got to have a CPU, connectors, memory and a printed circuit board. Then you've got to pay to put them in a box, ship them around the world, and even though we are non-for-profit some of our partners have got to make some money."

"We're doing the Model A for $25 next year I imagine in 2-3 years' time it'll be possible to do a board for $20. But it will be difficult to get below $20, even if you make various components for free.

"We want to keep these platforms on active development for at least two more years. People are just starting to get value and power out of the Model B, which is why we won't just rush out an upgrade. A hardware refresh in early 2015 is feasible," he told IT Pro.

I expect the Model B to carry on shipping until 2020, but won't be the lead model, it'll be part of a portfolio.

Upton, founder of the UK-based charity, and winner of the reader-voted IT Pro 2012 award for Tech Leader of the Year , told us that a portfolio of devices will develop over time, and the price of boards will likely drop to $20.

Upton suggested that the Foundation has no plans to make radical changes to the design, particularly the core component a Broadcom BCM2835 SoC. The chip is based on ARM architecture and despite running at just 700MHz, it is capable of high-end tasks such as Blu-ray and H.264 playback at up to 40MBits/s.

Upton explained that the existing chip gives the right balance between performance, cost and efficiency.

"The existing processor has a lot of legs so we're working hard to optimise the software. If you go back and run an April software image on a Pi and run an updated image, you wouldn't recognise them as the same machine," he continued.

"If we picked another processor it would be more expensive and we'd probably see a drop in the graphics performance. Our aim is to step forward in every direction."

Despite the refresh in the pipeline, Upton said that users who have invested in a Model B ($35) or plan to buy the forthcoming Model A ($25) shouldn't worry as software support will continue for a long time yet.

In fact, he is so confident in the longevity of the first generation models that he expects them to continue shipping until at least 2020.

"Even if we were to refresh the hardware we'd still support existing devices. I expect the Model B to carry on shipping until 2020, but won't be the lead model, it'll be part of a portfolio," he added.

"Given the choice between spending a little bit of money on every new Pi by putting a faster processor or spending more money to optimise the software for the benefit of all Pi users, it's a simple decision."

Upton told us that he expects one million Pis to be sold when the first anniversary rolls around in February 2013. Half of these boards are expected to have been made in South Wales, where a Sony manufacturing plant is currently producing 660 Raspberry Pis per hour.