Eprom emulators are used for eprom based development and EFI or ECU work. The emulator plugs into the socket where an eprom goes and looks just like the eprom to the computer system. Changes to the content of the EPROM's memory space is immediately available to the processor. No need to reboot or restart the system.
For starter information about EFI or ECU work using an emulator, see efi-ecu-FAQ pageSoftware updates