Western Digital Blue WD20SPZX Technical Reference Manual page 64

Glossary
The controller performs a logical-to-physical address conversion and retrieves the data from a
physical location in the storage device.
Logical Block Address: An alternative addressing methodology of identifying a given location
on an SATA drive that permits disk sizes greater than 528 MB.
Perpendicular Magnetic Recording (PMR): In PMR, the magnetization of each data bit is
aligned vertically rather than longitudinally to the spinning disk. The adjacent bits attract
instead of repel (as with bar magnets placed side by side), creating more thermally stable
bits.
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.
Reduced Power Spinup (RPS): WD's optimized start up feature specifically designed for the
external hard drive and Consumer Electronics (CE) market. Specific focus for RPS is to
minimize the duration and magnitude of the peak power consumption from the hard drive.
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 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): Serial ATA is the bus interface for 2.5 inch hard drives.
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 172-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.
Write Cache: A feature in CacheFlow that posts "command complete" prior to completing
the actual write.
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