Auto-boot EPROMs
Auto-boot EPROM chips are available form TRS-80 Models III, 4, and 4D. See here for pricing information.
The Model 4P is already autobooting and does not require a new EPROM.
These devices will allow your TRS-80 to boot directly from the CF hard drives without the use of a floppy diskette. Installing an EPROM requires opening your TRS-80's case and accessing the mainboard to replace a socketed chip. Some experience working with computer electronics is highly recommended.
The EPROM for a Model 4 Gate Array is different from the Model 4 non-Gate Array computer, so you will need to specify which one you need. The Model 4 Gate Array machine has the 25-pin RS-232 D-sub connector on its back. For the non-Gate Array, it is on the bottom of the machine.
With an auto-boot EPROM installed, hold down <SHIFT> during boot to force a boot from floppy instead of the hard drives.