Ultra SCSI
Provides 20 MB/s transfers over an 8-bit bus or 40 MB/s transfers over a 16-bit Wide SCSI bus. Also known as Fast-20 SCSI, this feature is most commonly found in SCSI-3 drives.
Ultra DMA/33
A high-speed host data transfer feature that transfers data at 33.3 MB per second.
Un-correctable Error
An error that cannot be overcome using Error Detection and Correction.
Unformatted Capacity
The total number of usable bytes on a disk, including the space that is required to record location, boundary definitions, and servo data. (See also formatted capacity.)
Universal Serial Bus (USB)
A serial bus with a bandwidth of 1.5 megabits per second (Mbps) for connecting peripherals to a microcomputer. USB can connect up to 127 peripherals, such as external CD-ROM drives, printers, modems, mice, and keyboards, to the system through a single, general-purpose port. This is accomplished by daisy chaining peripherals together. USB supports hot plugging and multiple data streams.
Unrecoverable Error
A read error that cannot be overcome by an ECC scheme or by rereading the data when host retries are enabled.
Untagged Queuing
The ability of the drive to receive a maximum of one I/O process from each initiator.
Upgrade
In hard drives, the replacement of a hard drive with one offering greatercapacity or performance, or both.