Hey S.U.,
The upper triangle button is the reset button. Here's the description from the Service Source:
"12 Chapter 1
Restart the computer.
Often you can eliminate a problem simply by restarting your computer, which clears the computer’s memory. Always try restarting the proper way:
1 If you can, save any open documents before restarting.
2 Open the Special menu and choose Restart.
Note: You can also press the power button (picture of the power button symbol) on your Apple USB keyboard or on the
front of the computer.
A dialog box appears.
(picture of shutdown dialog box)
3 Click Restart.
If the computer freezes: Try quitting open applications. See “Quit open applications.” onpage 13.
Force your computer to restart.
m If you are unable to restart your computer as described above, try pressing the
Command (command symbol) and Control keys simultaneously while also pressing the power button (power button symbol) on your Apple USB keyboard or on the front of the computer.
m Open the cover on the side of your computer and locate the Reset hole (it’s the upper hole on the right side, between the Ethernet and modem ports). Carefully insert the end
of a large straightened paper clip into the hole and push gently. Do not use excessive force. Your computer should restart.
m If neither of the above suggestions work, unplug your computer. Wait at least 30 seconds,
then reconnect the power plug and turn your computer on by pressing the power
button (¨) on your Apple USB keyboard or on the front of the computer.
If this doesn’t solve your problem, return to “Problems” on page 7."
The lower button is referred to in the manual as the "interrupt"button. There is no other reference to it in the manual but it reminds me of the "program interrupt button" or the programer's button on the old Bondi Macs G3s.
http://en.wikipedia.org/wiki/Programmer%27s_key
If you Google those terms you'd find a lot of info.
Richard
