Western Digital Re EX800M Technical Reference Manual page 57

EX800M Glossary
MicroFemto Slider — These drives incorporate the next generation femto slider form factor in which the read/
write head is mounted on the small, lightweight microfemto slider that allows the head to move more quickly
from track to track on the disk.
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.
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 hard drive products manufactured and sold worldwide
after June 8, 2011, meet or exceed Restriction of Hazardous Substances (RoHS) compliance requirements as
mandated by the RoHS Directive 2011/65/EU. 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.
Rotary Acceleration Feed Forward (RAFF) — These drives employ RAFF technology to maintain hard drive
performance in high vibration environments through adaptive compensation of the servo system.
Rotational Latency — The amount of delay in obtaining information from a disk drive that can be attributed to
the rotation of the disk. For a disk rotating at 10,000 RPM, the average latency is 3 milliseconds.
RPM (Revolutions per Minute) — Rotational speed of the media (disk), also known as the spindle speed.
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 Encrypting Drive (SED) — An optional secure model for encrypting and repurposing the drive utilizing an
AES 256-bit encryption engine for Crypto erase capability.
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.
StableTrac™ — The motor shaft is secured at both ends to reduce system-induced vibration and stabilize
platters for accurate tracking, during read and write operations.
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.
Time-Limited Error Recovery (TLER) — TLER prevents hard drive error recovery fallout by limiting the time
the drive spends in error recovery, providing increased performance, improved availability, and lower total cost
of ownership in RAID arrays.
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.
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