The idea that "virtualization" began with Zen in 2004 is rather difficult to read as an early VMware employee. Before QEMU independently discovered it, VMware was JIT'ing unrestricted x86 to a safe x86 subset from 1999 on[1]. Hardware support for trap-and-emulate virtualization came to the market in the early 'aughts after VMware had proven the market demand for it.