(Answered my query re memory in the Insanely-thin newer 21/5" iMacs too:
http://www.everymac....ros-and-cons.html

ie. no Firewire 800 [no biggie for mere backups]
no bloody optical drive [PITA]
Apple does not support end-user RAM upgrades on the 21.5-Inch models at all. It is neverthless possible, it is just needlessly difficult.
And:
The hard drive and processor both are difficult to upgrade.
Costs more than previous..

ie They want even-More of our Money and.. I continue to wonder re TEMPS inside that cutesy too-tiny enclosure, esp. given what I found in my '08 Model A1224 showing for GPU temp--default. Sans smcFanCtrl, in summer this sucker would have cooked that most-fragile of the guts chips!


It certainly is unfortunate that Apple decided to make it so difficult to upgrade the RAM on the 21.5-Inch model. In particular, using adhesive to attach the display to the chassis -- rather than magnets like previous Aluminum iMac models -- is a design decision that is inelegant at best. As Apple does not consider the RAM in the 21.5-Inch "Late 2012" and "Early 2013" iMac models to be a "customer installable part," EveryMac.com cannot recommend that users perform the upgrade themselves.

Most interested in the 21.5-Inch model likely should instead consider upgrading the RAM at the time of purchase -- which unfortunately means paying a higher upfront price overall due to a significant markup on RAM -- or alternately hiring a professional to perform the upgrade.

If it is important to you to be able to upgrade the RAM yourself, particularly as higher capacity memory modules may become available in the future, you may instead prefer to avoid the 21.5-Inch "Late 2012" and "Early 2013" iMac models altogether in favor of the 27-Inch "Late 2012" model or instead purchase an earlier 21.5-Inch iMac model on the used market with RAM that is easy to upgrade.




Well, I can manage to disembowel the sucker (new sticky tape == Where Get?) ..but the mech. inept had best not DIY.
But my TEMP question remains unanswered re the '11/'12-up small iMacs..

DAMN.. this means I gotta keep this iMac alive as long as possible, as Apple slouches towards Beastware-grade greed and cuteness über Practicality. :-/ :-/