I just replaced the idprom (AKA NVRAM + battery; I used an ST M48T08-100PC1) in my Sun SPARCstation 20. The original one was inside a rectangular holder with a tab on each short end; it had passthrough holes on the inside so the pins of the chip could connect to the motherboard.
I was having trouble getting my system to boot (as far as I can tell, I just needed to wait for it to go through the lengthy POST, since the only output you get during that is keyboard LEDs and terminal output), so I tried inserting the new chip directly into the motherboard (without the enclosure), and I found that it worked.
What is this thing called? And what is it used for?