Q: Can you put a 500mb ram stick into a iMac

No your mid 2011 iMac will be using DDR3 whereas the older eMac is using DDR which is not compatible physically nor electronically.

No. The type of RAM that old eMac used is completely different than that your iMac uses. Just get RAM designed for your iMac. You can get a 2GB kit for under $28.00 US, and a 4GB kit for under $50.

Regards.

Your year and model IMac can take up to 32 GBs of RAM.

Correct and reliable Mac RAM can be purchased from online Mac RAM sources Crucial memory or OWC (macsales.com).

Here's a link to the RAM you need from OWC.

http://eshop.macsales.com/shop/memory/iMac/2011/DDR3_21.5_27

Good Luck!

Contact OWC and be prepared to give them the serial number of your computer so they can match the correct RAM to the build model year series; the upgrade may involve more than one pair should you wish to get a proper match and a higher upgrade than you may know is possible.

Find out more, about your computer if you use an

identify by serial number online service, like this:

http://www.powerbookmedic.com/identify-mac-serial.php

You can find out more about most Mac computers,

if you get the download http://mactracker.ca

Both of the above can help learn more about upgrade options

and standard features in various build model years of Mac.

General mac RAM incl. 21.5 inch mid 2011 iMac:

http://eshop.macsales.com/shop/apple/memory/

•How to remove or install memory:

http://support.apple.com/kb/HT1423

Good luck & happy computing!

edited

Nope, that's 240 pin RAM, you need 204 pin.