The file system cache is used, by default, whenever a disk is accessed. However, applications can request that its files not be cached by using the FILE_FLAG_NO_BUFFERING parameter in its call to open a file. This is called unbuffered I/O. Applications that use unbuffered I/O are typically database applications (such as SQL Server) that manage their own cache buffers. Unbuffered I/O requests must be issued in multiples of the disk sector size.