Western Digital Blue WD20SPZX Technical Reference Manual page 63

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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.
Data Transfer Rate to Disk: The internal disk transfer rate in Mbits per second.
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Data Transfer Rate from the Buffer to the Host: Based on the transfer of buffered data in
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MB 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.
Glossary
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