Digital Storage Capacity ：250 GB /500 GB / 1TB / 2TB. Bus Type：PCIe Gen 3.0x4. DDR2 for desktop. DDR3 for desktop. 1MB=1000KB. It is calculation difference between manufacturer and your PC. Your PC says 1GB = 1.073741824 Billion bytes where Market Defines 1 GB = 1.00 Billion bytes.