U

UART

Universal Asynchronous Receiver/Transmitter. A module composed of a single integrated circuit, which contains both the receiving and transmitting circuits required for asynchronous serial communication.

UNC

Universal naming convention.

Unimodem

Universal modem driver. A driver-level component that uses modem description files to control its interaction with the communications driver, VCOMM.

UPS

Uninterruptible power supply. A device connected between a computer and a power source that ensures that electrical flow to the computer is not interrupted because of a blackout and, in most cases, protects the computer against potentially damaging events such as power surges and brownouts.

URB

USB request block. Clients send URB transfers to the bus by including a pointer in an IRP to a URB structure; a function within the URB identifies the specific request.

USB

Universal Serial Bus. A bidirectional, isochronous, dynamically attachable serial interface for adding peripheral devices such as game controllers, serial and parallel ports, and input devices on a single bus.

USB class

The class of filters under WDM that provides a bus interface and bus enumerator for USB.

User mode

For Windows and Windows NT/Windows 2000, the nonprivileged processor mode in which application code executes, including protected subsystem code in Windows NT/Windows 2000.

User-mode drivers

Win32-based multimedia drivers and VDDs for MS-DOS–based applications with application-dedicated devices. For more information, see the Multimedia Drivers and Virtual DOS Drivers documentation in the Windows 2000 DDK.