The dx4 is a sled that allows for 4 ssds on one pcie slot. See link for details. http://www.transintl.com/store/category.cfm?Category=2799 Because the conversation might eventually drift to an inquiry about the intended use, I will provide that upfront fwiw. thinking about 4 ssds, 3 for scratch, 1 for boot and apps. That would leave the four internal Sata bays plus the empty optical for my data on 5x HDD, raid 5. I'm planning on purchasing an Areca 1800 series raid card. Thanks!