Understanding which RAM chips are compatible with a Mac I'm upgrading an eMac to 1 GB RAM (2 x 512 MB). A dude is selling the following chips, but I don't know what CL3, CL2.5, SDRAM, SDCL3, 168P and DIMM means. Could someone please explain what these terms mean, and most importantly: Which ones will work on the Mac?

1 x Kingston   512MB 133MHz CL3
1 x RAMOS TEK  512MB 133MHz CL2.5
1 x Samsung    512MB PC133 SDRAM
1 x TwinMOS    512MB PC133 CL3
1 x Winbond    512MB PC133 SDCL3
3 x Transcend  512MB PC133 SDRAM 168P DIMM
You never mentioned which eMac you specifically had, but according to EveryMac.com, there are only two possibilities:


PC 133 SDRAM.  Compatible with 2002 through 2003 models.  
PC-2700 SDRAM.  Compatible with 2004 through 2005 models.


Both machines require 184pin modules

CL numbers have to do with the latency of the memory (CAS Latency) or in other words, how many clock cycles before it transfers data.  Lower numbers are faster.

SDCL3 just looks like a manufacturer "smashing" together of SDRAM and CL3.  

DIMM is "dual in-line memory module."  Basically, there's memory paths on both sides of the module (as opposed to SIMMs).  

For more info, see this article on RAM types.

As for which memory will work in your eMac, it's impossible to say for sure because they're all (with the exception of the Transcend memory at 168 pins) missing the pin count.  If they are 184 pins, then they should work.