The funny thing is that the 4004 was used in emulation from pretty much it's beginning. It was used to make a calculator, the Busicom 141-PF. But the calculator

The funny thing is that the 4004 was used in emulation from pretty much it's beginning. It was used to make a calculator, the Busicom 141-PF. But the calculator couldn't be programmed in 4004 directly. 4004 ran virtual machine. The calculator was written in the virtual instruction set for this machine. A chip like the 4004 could be used in some simple embedded applications using its instruction set directly. But that calculator was the original application was developed for. Already that was too complicated, not unlike, say, booting Linux.