This is the first system I built, and I used Win 8.1 as the OS. The 128gb Kingston SSD is the boot drive and works fine. I installed a previously used 640 WD HD and it also works fine. However the new WD BLACK SERIES WD1003FZEX 1TB 64MB Cache SATA 6.0Gb/s 3.5" Internal Hard Drive is visible in Win 8/1 disk management and in Win Explorer, but I can not write to it, format it or partition it. I did add it after the system was installed.