Eben Upton has been telling IEEE Spectrum about the move to Raspberry Pi 4 and how the format is evolving.

”The last three Pis have all been made using the same  process,” says Upton (pictured), “so modifications have been limited, mostly putting in a larger ARM. If you look at the floor plan of the chip, each new ARM gets stuck on the left-hand side.”

”The chip stretches horizontally and becomes bigger and bigger,” adds Upton, “but nothing on the right-hand side changes, and the right-hand side is where the memory controller is, where the UARTs are. But putting in a larger ARM core means your power goes up and eventually you run out of your thermal budget.”

”We realized we needed to go to a 28-nm process node. And once you’re going to a new process node, you might as well fix all of the wrinkles. And that’s why you see two displays, many UARTs, PCI Express, Gigabit Ethernet.”

Shrinking forever is no longer an option and Upton accepts that

“I think it’s relevant to think in terms of how much is left,” says Upton, “how much for a given thermal footprint? We’ve come a factor of 40. There’s not another factor of 40 left, which means you’ve come through more than half this process. On some level that’s intimidating. But I’m a software engineer. It’s actually really nice to feel that we’re going into an era where software engineering makes a contribution again!”