This is an insane question but, where is the block of hardware known as my startup hard disk? I have three physical disks which consist of a total of four partitions, all visible and accessible in Finder. One of the disks is partitioned for Bootcamp, hence 4 partitions. I just opened the cover of my Mac Pro (2008) to investigate the annoying sine wave resonance that, according to other posts that I find here, is not uncommon at all. I was kind of expecting to see three of the HDD slots occupied, but instead I find two empty, and two occupied, none of which are the SSD. I know that the SSD is physically smaller than the HDDs are, but maybe I've had my memories messed with when I moved from Mac Mini to this machine, and in order to rescue the files from the old disks which are physically smaller, they had to be sort of taped to the brackets in order to stay in place temporarily. But the pins matched. Online search nor repair manual brought luck in trying to interpret the system info, where the SSD might reside. What does "Lower" refer to, anyway? Connection Bus : SATA Connection ID : "Lower" Device Tree : IODeviceTree:/PCI0@0/SATA@1F,2/PRT1@1/PMP@0 Bay : "Lower"