Some full forms for "U":

In computing world we Always use abbreviate form for almost all the things we came across,here are some full forms for you.
ATA-Advanced Technolongy Attachment
SATA-Serial ATA
IDE-Integrated Dirve Electronics
CMOS Battery-Complementry metal-oxide Semicondutor Battery
SMPS-Switched Mode Power Supply
VGA-Video Graphics Adapter
HDD-Hard Disk Drive
USB-Universal Serial Bus
NVRAM-Non-Volatile Random Access Memory