New hard drives are increasing their sector size (the smallest unit of data that you can physically read or write to the disk) from 512 bytes to 4096 bytes. This is required to allow disks larger than 2 terabytes. You can emulate the old sector size, but at a loss of performance. Linux and Mac systems are already optimized for the larger sector size, but Windows 7 is the Microsoft system with best support.
Meanwhile, SSDs have a physical unit of 512K (a half megabyte). This is the smallest block of data that you can erase, and you have to erase data before you can rewrite it. This poses a different block size problem for the OS, filesystem, and application.