Glossary - Western Digital WD15NPVX Technical Reference Manual

WD Green MB500M-6Gb

Glossary

8.0 G
LOSSARY
Active LED Status - WD SATA drives support external LED requirements. It provides an activity LED output
which is ON during command execution and OFF otherwise.
Advanced Format (AF) — Technology adopted by WD and other drive manufacturers to increase media
format efficiencies, thus enabling larger drive capacities.
Annualized Failure Rate (AFR) - A method of measuring failure rates or trends for a group of units at a site.
The rates are based on the monthly total number of returned field failure units divided by the total cumulative
installed base and multiplied by 12 (to annualize the failure rate).
Automatic Defect Retirement - If defective sectors are found during a read or write, they are automatically
mapped out and relocated.
Block - A group of bytes handled, stored, and accessed as a logical data unit, such as an individual file record.
Buffer - A temporary data storage area that compensates for a difference in data transfer rates and/or data
processing rates between sender and receiver.
Data Lifeguard™ — Representing WD's ongoing commitment to data protection, Data Lifeguard data
protection utilities include thermal management, an environmental protection system, and embedded error
detection and repair features that automatically detect, isolate, and repair problem areas that may develop over
the extended use of the hard drive.
Data Transfer Rate -The rate that digital data is transferred from one point to another, expressed in bits per
second or bytes per second.
Defect Management -A general methodology of eliminating data errors on a recording surface by mapping out
known bad areas of the media.
ECC On-the-Fly -A hardware correction technique that corrects errors in the read buffer prior to host transfer
without any performance penalties. These error corrections are invisible to the host system because they do not
require assistance from the drive's firmware.
Error Correction Code (ECC) -A mathematical algorithm that can detect and correct errors in a data field by
adding check bits to the original data.
F.I.T. (Functional Integrity Testing) - A suite of tests WD performs on all its drive products to ensure
compatibility with different hosts, operating systems, application programs, and peripherals. This testing must
be performed before the product can be released to manufacturing.
Fluid Dynamic Bearings (FDB) - A bearing design that allows ultra-low rotational drag while providing high
lateral stiffness to steadily hold the spinning center of the diskpack for high-accuracy of reading and writing of
data.
Formatted Capacity - The actual capacity available to store data in a mass storage device. The formatted
capacity is the gross capacity minus the capacity taken up by the overhead data required for formatting the
media.
Hot Plugging - The ability to swap out a failed hard drive without having to power down the system or reboot.
Latency - The period of time that the read/write heads wait for the disk to rotate the data to an accessible
position. For a disk rotating at 5400 RPM, the average latency is 5.5 milliseconds.
Logical Address - A storage location address that may or may not relate directly to a physical location. The
logical address is usually used when requesting information from a controller. 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.
2679-771422-A00 RELEASED 5/2/13 (WD CONFIDENTIAL) 43