Hi. Anybody have experience with using a 4TB internal HDD in the iMac 24? If so, what brand and model drive did you use? I need help with a puzzling 4TB HDD issue in my early-2009 iMac 24 (iMac9,1; OS X 10.6.8 Snow Leopard; 8GB RAM). I'm trying to replace the original 1TB internal HDD with a Western Digital Black 4TB 3.5" HDD: model WD4004FZWX, SATA III, 7200 rpm, 128MB cache. I formatted the drive in an external USB enclosure, used SuperDuper! to clone the data from the original drive, and verified that the new 4TB drive can externally boot my iMac. However, when I swapped the drives and tried to boot from the new 4TB drive internally, I got the flashing "?" folder symbol. I put the original 1TB drive in the external enclosure and booted externally from that, and the iMac does not even see the new 4TB drive. It's missing from the Desktop and Finder, and it's not listed in Disk Utility or System Profiler's Hardware Serial-ATA tree. I swapped the drives back, booted from the 1TB drive internally, and the Finder and Disk Utility see the 4TB drive externally, but as an unformatted disk ("The disk you inserted was not readable by this computer.")! I thought the 4TB drive might be defective, so I exchanged it for a new one, but I got the same results with that one as well. Also, I tried resetting the PRAM and the SMC in the course of troubleshooting, but that didn't help. At this point, I think the issue is with the iMac 24's NVidia MCP79 SATA controller not being compatible with the WD4004FZWX's disk controller, since the NVidia MCP79 is not fully compatible with a number of SSD controllers. So the NVidia MCP79 is finicky. I found instructions on the Western Digital website on using a jumper to restrict a SATA III drive to SATA II speeds, but the WD4004FZWX doesn't have a full set of 8 jumper pins (the drive has pins 3 & 5 only, but pins 5 & 6 need to be jumped): https://support.wdc.com/knowledgebase/answer.aspx?ID=981 I'm planning to return the WD4004FZWX and try a different 4TB drive. Please let me know your experience or advice with using a 4TB HDD in the iMac 24. Thanks.