Startup key sequence to enter EFI

There is none sorry... It is not user configureable.

Power Mac G5 Dual 2.5 (June 2004) Mac OS X (10.4.4) 23" Cinema Display, 3 GB of RAM, 550 GB HDD

Is that absolutely true?

It's bad new if it is - no access to allow emergency repairs (with or without AppleJack), I find this a strange decision.

I've only ever used one EFI based machine (and it wasn't a Mac) but the EFI shell was accessible via the boot manager. Try holding down option while booting a new iMac and see what choices are available.

ShelbyCR67 may be right though, it may not be user accessible.

Yes, it is true. Apple's implementation of EFI has no user-accessible shell.

The EFI shell is apparently not installed on the new iMacs. However take a look at the man page for bless(8) by running 'man 8 bless' in Terminal.app.

I tried the bless parameters that were provided in another forum and either I'm not providing the correct paths or bless doesnt work. I did also see some talk of the fact that Vista does not yet support EFI [it will fully support it down the road]. What we need to do is find someone that can confirm which OS has full EFI support and then start from there. Vista build 5270 [and the bless paramaters that I used] did not work.

I dont have the iMac yet. I tested the bless options provided on an Intel iMac that I had access to.

Somebody appears to have found a way in!

No. What they did was boot into an Intel EFi test interface that they downloaded and installed. The Mac EFI still has no user accessible interface.

Careful messing around with that. Several people have already hosed their new iMacs beyond user repair by throwing commands at the EFI firmware.

Once you break it, you are done. You can't zap your PRAM or NVRAM if the firmware that listens for those keys at startup never actually comes up. =( You are just hosed for good at that point.

When my MacBook arrives, I will not be messing with this sort of thing at all. I value my money too much to have a $2000 paperweight.

I see, and I agree that this will not be an option for me either - the loss of a firmware interface is a major concern though.