Western Digital caviar blue xl500s Technical Reference Manual page 56

Glossary XL500S
Latency — The period of time that the read/write heads wait for the disk to rotate the data to an
accessible position.
Logical Block Address — An alternative addressing methodology of identifying a given location on a
SATA drive that permits disk sizes greater than 528 MB.
Native Command Queuing (NCQ) — NCQ allows the drive to re-order read commands, thereby
increasing random read IOPs. NCQ is a true Enterprise feature for environments such as database,
Web servers, and e-mail servers.
NoTouch™ Ramp Load Technology — The recording head never touches the disk media ensuring
significantly less wear to the recording head and media as well as better drive protection in transit.
Pre-emptive Wear Leveling (PWL) — WD feature that provides a solution for protecting the
recording media against mechanical wear.
PRML (Partial Response Maximum Likelihood) — A read channel using sampled data, active
equalization and Veterbi detection to accurately retrieve the user data off the disk.
RoHS (Restriction of Hazardous Substances) — WD complies with the Restriction of Hazardous
Substances (RoHS) Directive 2002/95/EC of the European Parliament, which is effective in the EU
beginning July 1, 2006. RoHS aims to protect human health and the environment by restricting the use
of certain hazardous substances in new equipment, and consists of restrictions on lead, mercury,
cadmium, and other substances.
Rotational Latency — The amount of delay in obtaining information from a disk drive that can be
attributed to the rotation of the disk.
RPM (Revolutions per Minute) — Rotational speed of the media (disk), also known as the spindle
speed. Hard drives spin at one constant speed. The slower the RPM, the higher the mechanical
latencies. Disk RPM is a critical component of hard drive performance because it directly impacts the
rotational latency of the disk transfer rate.
Seek Time — The time it takes for the read/write head to move to a specific block of data on the hard
drive. The average seek time is computed by dividing the time it takes to complete a large number of
random seeks by the number of seeks performed.
Sector — A 512-byte packet of data.
Self-Monitoring, Analysis, and Reporting Technology (S.M.A.R.T.) — A technology to assist
the user in preventing possible system down time due to hard drive failure.
Serial ATA (SATA) — SATA is the next generation bus interface for hard drives. It is designed to
replace Parallel ATA, and has many advantages including increased transfer rate, improved signal
integrity, enhanced data protection, and hot plugging.
S.M.A.R.T. Command Transport (SCT) — The SCT Command Transport feature set provides a
method for a host to send commands and data to a device and for a device to send data and status to
a host using log pages.
Staggered Spinup — SATA feature that allows the system to control whether the drive will spin up
immediately or wait until the interface is fully ready.
Thermal Asperity — A thermal asperity is a baseline shift in the readback signal due to heating of the
magnetoresistive stripe on the head as a result of physical contact with the disk or a particle.
Unrecoverable Error — A read error that cannot be overcome by an ECC scheme or by rereading
the data when host retries are enabled.
World Wide Name (WWN) — The World Wide Name (WWN) defined in ATA/ATAPI-7 is a
modification of the IEEE extended unique identifier 64 bit standard (EUI-64) and is comprised of three
major components: naming authority, organizationally unique identifier (OUI) and serial number. WD's
OUI is 0014EEh.
Write Cache — A feature in CacheFlow that posts "command complete" prior to completing the
actual write.
48 RELEASED 10/21/10 (WD CONFIDENTIAL) 2679-701211-A06