Member-only story
Linus Called It a Failure. Two Companies Living in It Sold for $1.1 Billion.
VMware and Cambridge’s Xen both ran guest kernels in x86’s ignored ring 1, and Amazon built EC2 on one of them.
A pub bet and an empty floor
Since the 80286, x86’s protected-mode privilege system has been built like a four-story building. Hardware engineers laid out four privilege levels in silicon, reserving the penthouse for the kernel and the ground floor for applications.
Intel numbered the floors from the top down: ring 0 is the penthouse, ring 3 the ground floor, and rings 1 and 2 the two floors in between.
Between the executive suites and the lobby, rings 1 and 2 stood dark and empty.
In 1999, Ian Pratt and his students started the XenoServers project inside the University of Cambridge Computer Laboratory. They set out to sell computing time to strangers across shared machines, framing an audacious requirement: serve both Coke and Pepsi from a single computer, with both rivals confident about the arrangement.
Two corporate enemies had to share the same physical box without seeing through the walls.
