Glossary of Hard Disk Drive Terminology (Letter U)

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.)

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.

In hard drives, the replacement of a hard drive with one offering greatercapacity or performance, or both.