I discovered thanks to free software Mactracker my iMac 2008 (Version 8.1) supported 6GB of memory instead of the announced by Apple 4G0. This made me very interested because occasionally the iMac seemed to falter because I seek much (in SnowLeopard). So I replaced original 2GB memory slot 0 by the bar 4GB of Komputerbay (slot 0 is the location right when the mac is lying front against a table). the new ram was immediately recognized and successfully tested by TechTool 7 Since I ask a little more imac without much worry about the ram available which suits me perfectly