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UART (Universal Asynchronous Receiver-Transmitter chip) A chip that controls serial ports. It sets protocol and converts parallel data bits coming from the system bus into serial bits.

UDP (User Datagram Protocol) A connection less protocol that does not require a connection to send a packet and does not guarantee that the packet arrives at its destination.

Ultra-SCSI Also called Fast-20 or Fast SCSI. A technology that offers 20 MB/sec burst transfers across 8-bit paths and 40 MB/sec burst transfers across wide 16-bit paths.

UMB (Upper memory block) A group of consecutive memory addresses in RAM from 640K to 1 MB that can be used by device drivers and TSRs.

UNDELETE command A DOS command that retrieves previously deleted files, provided that their locations have not been written over.

UNFORMAT command A DOS command that performs recovery from an accidental FORMAT, and may also repair a damaged partition table if the partition table was previously saved with MIRROR/PARTN.

UNIX A multi-user, multiprocessor operating system developed by AT&T in the early 1970s. It exists in various forms and implementations and is the predominant operating system used by the Internet servers. It is not, however, required by the user to access the Internet.

Upper memory The memory addresses from 640K up to 1,024K, originally reserved for system BIOS but now used for device drivers and TSRs.

UPS (Uninterruptible Power Supply) A device designed to provide a backup power supply during a power failure. Basically, a UPS is a battery backup system with an ultrafast sensing device.

URL (Universal Resource Locator) A unique address that identifies the domain name, path, or filename of a World Wide Web site. Microsoft's URL address is: www.microsoft.com

USB (Universal serial bus) A bus developed by Intel Corporation, intended to be used by low-volume I/O devices such as modems, joysticks, touch pads, trackballs, and mice.

User account In Windows NT, the information, stored in the SAM database, that defines an NT user, including user name, password, memberships, and rights.

User documentation Manuals, online documentation, instructions, and tutorials designed specifically for the user.

User mode The portion of Windows NT that provides an interface between the OS and applications or users. User mode has access mode.

User profile In Windows NT, a personal profile about the user kept in the NT registry, which enables the use's desktop settings and other operating parameters to be retained from one session to another.

Utility program/ software A program designed to perform maintenance work on a system or on system components, e.g. a storage backup program, a disk and file recovery program, or a resource editor.