| Term | Description |
| UART | Universal Asynchronous Receiver/ Transmitter. A communication chip that converts parallel bytes into singular bits for serial transmission over modems and serial ports. Because it's not synchronized with the system clock, a UART chip also has the receiving and transmitting circuits needed for start and stop signals that tell the communicating devices when a packet of information starts and ends. |
| Universal Resource Locator | See URL. |
| Upper Memory | Upper Memory is the memory addresses between 640K and 1024K. On the DOS Memory Map, Upper Memory is that area between Conventional Memory and Extended Memory reserved for System BIOS and video information. Also called Reserved Memory. |
| UPS | Uninterruptible Power Supply. A UPS is basically a battery back-up system for your computer. It acts as a surge suppressor, filtering line noise and providing protection against spikes. But, in the event of a power outage it keeps your computer up and running, sounding an alarm and allowing you to close any running programs and shut down your computer safely. |
| URL | Universal Resource Locater. Simply, the address to a website on the Internet. To help better explain the parts, lets look at /glossaryu.htm. The 'http://' tells you the document type (it uses the HTTP protocol). Next, 'www' tells you it's on the World Wide Web and 'pccomputernotes' is the domain name (the name of the computer where the document is stored). The '.com' tells you the type of domain (commercial, in this case), and the 'glossaryu.htm' is the name of the document. If you don't see a document name (eg. ) then it displays the default document for that domain, usually 'default.htm' or 'index.htm'. |
| USB | A Universal Serial Bus is an external bus with a maximum transfer speed of 12 megabits per second. It's hot-swappable, which means that a device can be connected or disconnected while the computer is running. The Operating System can recognise and use the device as soon as its plugged in. Up to 127 devices can be daisy-chained together. |
| User Profile | A file kept in the Registry that contains a user's desktop settings and personal setup preferences to be retained from session to session. |