Western Digital WD15NPVX Technical Reference Manual page 52

Glossary WD Green MB500M-6Gb
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.
Rotational Latency - The amount of delay in obtaining information from a hard 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.
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.
Sector - A 512- or 4K-byte packet of data.
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.
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.
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.
System-on-Chip - The System-on-Chip (SOC) is the foundation for WD's next generation electronics and
firmware architecture. The native SATA SOC lowers component count by integrating a hard disk controller,
high performance processor, high speed execution SRAM, and read channel in a 128-pin package.
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.
44 RELEASED 5/2/13 (WD CONFIDENTIAL) 2679-771422-A00