The EFI firmware update would be applied to the hardware in the computer.
The logic board has a chip that stores those details; not on a hard drive.
Changing out the hard disk drive would not alter this fact; so there may be
different reasons for the computer not accepting a system install DVD, etc.
If you happen to have a late model G5 iMac PPC, it could look like the later
Intel-based Macs. You need to correctly identify the computer, since there
were many models built and they have different specifications.
If your computer looks like the newer pizza box models, it would be here:
Identify the model of your iMac - Apple Support
If the computer is like an iMac G4, it would be the model with the chrome
metal arm, and half-orb base, with the newest OS X it could run, 10.5.8.
Those were from about 2003 and are powerPC hardware. What is yours?
And if your computer is an iMac4.1 it would be one of these Intel models:
Both 17-inch and 20-inch iMac4.1 (intel-based) from Early 2006, note software.
Original OS Mac OS X 10.4.4 (8G1165, 8G1171, 8G1172)
Later OS Mac OS X 10.4.6 (8I2040)
Maximum OS Mac OS X 10.6.8
Hardware Test AHT 3A100, 3A103
• iMac EFI Firmware Update 1.1
Original media would be grey label, specific to the Intel based iMac model; with
part numbers intended only for use in the iMac4.1 (Intel. Not PowerPC G5/G4)
If you have a retail 10.5 OS X Leopard DVD, that should work; start with C key
held down and choose through the setup instructions; use Disk Utility from the
menu to set up (format) the hard drive in HFS+ Journaled... then the installer
can see the drive as ready for the full installation. Exit Disk Utility to complete
the installation. Have you previous experience with new system installation?
This EFI Firmware Update fixes several Boot Camp,
start up, & wake-from-sleep issues on iMac computers.
It was supplied & available back in 2006 in OS X10.4.6.
The computer should be able to boot into the Installer on the OS X DVD so as
to prepare the hard drive for a fully new installation; using its Disk Utility...
A host could be asked to relocate this thread to the Intel-iMac section for best
exposure; however there needs to be more information supplied, even so.
Good luck & happy computing! 🙂