The 6GB are, according to some forum entries of users in many successful on the run, (2GB in Slot 1 + 4GB in Slot 2).
Said 4GB SODIMM I found here at Komputerbay to a fair price in my opinion.
Module for testing times against the 2GB built-in slot 2 exchanged, iMac started and it was immediately recognized = 6GB RAM.
As weekend action then:
Full backup and manual backup made.
Then installed the 500GB SSD (here I was unfortunately not 100% matching 2.5 "to 3.5" HDD Adapter for iMac.
If anyone has found one, I ask for info !!!
Info:
Only the Festpaltte the iMac has a SATA interface
The SuperDrive for there SSD adapter kit is only PATA / IDE
Now in the current config to the already elderly iMac is afloat again and liquid to use on the go and for more "Old World all tasks" in the living room for all in the family.
The RAM of Komputerbay is for the RAM upgrade for the iMac 8.1 a clear recommendation for the laity, because the iMac does not need to be opened.
The replacement of the HDD or SSD reconstruction on I recommend only experienced hobbyists and not laymen!