In computing, FASTOPEN is a DOS terminate-and-stay-resident command, introduced in MS-DOS version 3.3,[1] that provides accelerated access to frequently-used files and directories.
[3] The command works with hard disks, but not with diskettes (probably for security when swapping) or with network drives (probably because such drives do not offer block-level access, only file-level access).
If a disk defragmenter tool is used, or if Windows Explorer is to move files or directories, while FASTOPEN is installed, it is necessary to reboot the computer afterwards, because FASTOPEN would remember the old position of files and directories, causing MS-DOS to display garbage if e.g. "DIR" was performed.
DR DOS 6.0 includes an implementation of the FASTOPEN command.
[5] The "fastopen" name has since been reused for various other "accelerating" software products.