U Interface
A 2-wire ISDN circuit, essentially today's standard 1-pair telephone company local loop made of twisted-wire. The U interface is the most common ISDN interface and extends from the central office.

UDF
Universal Disk Format. A file system developed by the Optical Storage Technology Association for storage of data on optical media.

UltraPack
A file and folder compression format that offers better compression than standard or HiPack compression.

Uniform Resource Locator (URL)
A naming convention that uniquely identifies the location of a computer, directory, or file on the Internet. The URL also specifies the appropriate Internet protocol, such as HTTP or FTP.

Universal naming convention (UNC)
A way to specify a directory on a file server. UNC names are file names or other resource names that begin with the string \\, indicating that they exist on a remote computer.

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.

User
One of three core components in Windows 98. It manages input from input devices, output to the user interface, and interaction with the sound driver, timer, and communications ports.

User profile
User-specific information contained in the file User.dat, which is one of the two files in the Windows 98 registry