U
universal serial bus (USB) A new external expansion bus that is popular for use with low-speed mass storage devices such as ZIP drives, modems, and printers.
upload The ability to transfer (send) a file from one computer to a remote computer.
upper memory area (UMA) The area from 640 KB to 1024 KB that is designated for hardware needs such as video RAM, BIOS, and memory-mapped hardware.
upper memory blocks (UMB) The unused spaces in upper memory that can be divided into blocks. These empty blocks have no RAM associated with them and are simply reserved space. This unused space is valuable because, unlike expanded and extended memory, MS-DOS can run programs in UMB.
UPS (uninterruptible power supply) Acts as both a surge suppresser and a power leveler to provide the computer with a constant source of power. It also provides power during a power failure or interruption so the user can safely save data before shutting down.
Usenet The vast collection of discussion groups and newsgroups on the Internet.