'We thought we'd sell 1,000': The inside story of the Raspberry Pi

...the rest of the industry's penchant for overhauling its products on an annual basis. Upton warns not to expect any imminent announcements about new versions of the Pi or substantial price changes.

"There will be a successor at some point. I think 2013 isn't the right time to do it. I don't want to orphan the 700,000 Raspberry Pis that are already out there," he said.

Upton prefers to focus on incremental upgrades to the existing boards. The model B has already received a boost to its memory, from 256MB to 512MB, and Upton is keen to stress the ongoing software optimisation, both by the Foundation and Pi users. The software, he points out, is just as important as the hardware.

"We can improve performance by further optimising the software. ARM 11 didn't see an enormous amount of targeted optimisation, so there's a lot of low-hanging fruit" — Eben Upton

"We can improve performance by further optimising the software. ARM 11 didn't see an enormous amount of targeted optimisation, so there's a lot of low-hanging fruit," he said.

"One of the things we've been doing recently is paying people to crawl over Linux, profile it, find out why it's slow and make it fast."

The benefits of this optimisation are evident when comparing the slightly sluggish desktop of the Linux Debian distro available for the Pi at launch to that of the relatively nippy Raspbian distro, which has been customised for the Pi's hardware.

By rewriting OS software functions to suit the Pi's ARM V6 architecture, underlying hardware operations have been sped up, for instance memcopy and memset operations were given a 2x and 7x speed boost respectively.

"If you talked to people who used the Pi from May through to now, in August people saw a really big kick-up in performance," said Upton.

Read this

Raspberry Pi cases round-up: Eight inventive holders in photos

• Read more

For Upton more important than making the Pi faster is making it easier to use, or at least easier to start programming on. He wants the Pi to boot straight into a programming environment like Scratch, the drag-and-drop programming tool made by MIT, much as the BBC Micro greeted you with a BASIC programming prompt when you turned it on.

"I'm a big fan of having it boot into a programming environment. It's Apple-like optimisation, taking options out of a platform to make it better," he said, adding that hidden features would be easy to gain access to if users wanted additional control.

Bug fixing is also an ongoing process for the device, particularly drivers for the Pi's USB controller, which has had a number of software bug fixes via kernel updates.

Most of the Pi's well-documented USB problems, Upton said, stemmed from the way that USB 1.0 traffic is packaged on top of the USB 2.0 link between the system-on-a-chip and the hub chip.

Upton said that while there had been a time when a number of USB peripherals were failing or not working as expected, there were now only problems in a handful of fringe cases.

Enter the Model A

The $25 Model A Raspberry Pi will also ship in the first quarter of this year. The board doesn't include the ethernet port, has only has 256MB of RAM — half that of the Model B — and only one USB port. The board consumes less power than the Model B and so is suitable for use in battery-powered robotics devices.

Upton said that while the 512MB board is suited to people who want to run the Pi as a computer, the 256MB is fine for people who want to use the board as a media centre, for robotics or embedded computing.

The Foundation originally planned to release the Model A last year but Upton said it had had to wait until its manufacturing partners were able to meet demand for the Model B boards before it could start selling the Model A, as both boards use the same Broadcom 2835 chipset.

Competitors

One factor that helped ensure the Pi's success is the lack of alternative machines offering the same mix of performance and capabilities at such a low price. Since the Pi's release other boards have gone on sale that have been touted as capable of snatching the Pi's low-cost crown. One example is the $49 Cubieboard, a 1GHz board based on the ARM Cortex A8 processor with 512MB or 1GB of memory.

The numbers might at first glance suggest these boards are faster and more capable than the 700MHz Pi. But Upton insists that in true performance terms, there is nothing on the market that has him worried.

He points out that the Cubieboard and other potential Pi killers are...