Eben Upton's overwhelming emotion at having co-created a $35 Linux computer that sold in the hundreds of thousands last year is surprise.
The 34-year-old chip architect is genuinely taken aback that demand for the Raspberry Pi proved to be orders of magnitude larger than a small pool of aspiring UK computer engineers.
"We honestly did think we would sell about 1,000, maybe 10,000 in our wildest dreams. We thought we would make a small number and give them out to people who might want to come and read computer science at Cambridge," he told ZDNet.
The first inkling of the fervour the credit card-sized board would create came in May 2011, when the first public outing of the Pi in a BBC video generated some 600,000 views on YouTube.
Upton and his colleagues revised their initial run of boards up to 10,000, thinking that would be more than enough to meet demand.
It wasn't. The 10,000 boards sold out within hours of going on sale in February last year, with an incredible 100,000 boards ordered on that first day.
Today more than 700,000 Raspberry Pi computers have been shipped to modders who are fitting them to robotic drones in the sky and underwater, to hobbyists designing home automation systems, and to wannabe coders looking to build their first programs.
So what, exactly, is the Raspberry Pi?
The Pi is a credit card-sized device and one of the lowest-cost computers available. At first glance it looks nothing like what is generally considered a computer, nothing more than a bare board and ports, but it is perfectly capable.
The board is powerful enough to stream 1080p video, browse the web or write documents, and it was designed to be portable enough to carry around without breaking. A number of distros of Linux run on the Raspberry Pi, including ArchLinux, Debian "wheezy" and Raspbian — a Pi-optimised version of Debian.
Raspberry Pi provides OS images for download here. Most are bundled with programming aids such as IDEs and the drag-and-drop programming software Scratch. Programming tools are easily available from the desktop and Upton wants future OS images to boot the board straight into a programming environment.
Putting these tools front and centre is designed to inspire tinkering. The Pi is there to encourage a similar taste for experimenting with computers that was inspired by the blinking Basic programming prompt of the Acorn BBC Micro in the 1980s.
The origin story
Despite engineering one of the unexpected computing success stories of 2012, however, Eben Upton and his colleagues didn't even set out to build a computer.
The Raspberry Pi Foundation was established with the goal of inspiring the next generation of programmers: it just turned out they felt the best way of doing that was to provide a computer cheap enough for kids and easy enough for them to hack.
"I looked at our founding documents and nowhere in there does it say 'We'll make a small computer'. What it says is 'We want to get kids programming'," he said, while giving ZDNet a tour of the Raspberry Pi factory in South Wales.
"The kids [coming to university to study computer science] haven't had the opportunity to do much programming before they come in the door," he said.
"It would have been heartbreaking if it turned out that kids aren't interested" — Eben Upton
"You've got to put in your 10,000 hours and it's a lot easier to put in the 10,000 hours if you start when you're 18," he said.
Despite Upton's belief that kids are still interested in coding, he was nervous about showing the Pi to young people for the first time, a fear born out of the received wisdom that they are interested in playing with smartphones and social networks but not the underlying technology that makes them work.
"I think I'd been avoiding testing my hypothesis just in case. We took them into a school a week before we launched and these kids went crazy for them," he said.
"It's been great to see that we had this theory that kids still want to program, and it would have been heartbreaking if it turned out that kids aren't interested."
Upton believes it is the feeling of being able to control a machine that gets kids hooked on programming in the first place.
"It's that sense of power in making a computer do a thing — it's 'I made a cat move'. Because the Pi's simple and bare bones if you make it do something, they seem to feel they can own it, more so than making a PC do something," he said.
Building the boards
Meeting demand far in excess of what the Foundation planned for posed a challenge. As the Pi was getting ready to launch, the operation to build and ship the boards — from booking factory time to purchasing the chips — fell to the relatively modest resources of the Raspberry Pi Foundation, a charitable body initially funded by loans from Upton and five other trustees.
"That would have been fine at 10,000 boards, but there was not a hope in hell that we'd be able to scale that up to build 100,000," he explained.
"We would have struggled in two ways...