Jim Razor

Unfortunately i will have to disagree with mayer... Not having torn your model of iMac down personally I will have to defer certain knowledge to others. If you look through this piece on everymac.com it states that the Late 2013 iMac does have a slot for a PCIe SSD whether or not the system was configured with a Fusion Drive from Apple. https://everymac.com/systems/apple/imac/...-aluminum-tapered-edge-faq/how-to-upgrade-imac-hard-drive-aluminum-2012-2013.html 'Remember this is NOT a PCIe slot that will take M.2 drive. It is a propriety slot that very few manufacture drives to this specification. So that said, you may find that your best option is OWC (they are good people, call them they will know what your options are and the best way to fill them). Lastly... you could simply replace your hard drive with a SSD and be done with it (your standard drive is a 5400 RPM drive rather than the faster 7200 RPM drives - ALWAYS use high quality SSDs, not the "cheepest" ones that are on sale at your local computer...

Andrew, did you get anywhere with your computers? We are a company that refurbs older Mac Pro's and a Top Seller on EBay... From the posts, you may have several issues... *the memory may be in the wrong slots - from what i read in your posts is that the memory is in the top slots of the memory risers... Mac Pros like their memory in the bottom slots (the ones closest to the edge connectors) *your choice of video cards may be problematic as others have suggested - a great generic video card for the 2008s is the ATi XT2600 - very good card and not too expensive OR use an NVidia 120GT (from the 2009 MPs) - you will not get a splash screen with NON-Apple video cards - this can cause you much stress as it may take several minutes for the computer to start with no video output until the last moments. *you may have old dust and such causing shorts and general confusion on the board - if you have not broken it down we would recommend that you do so and clean it all (compressed air and small soft brushes works...