Western Digital WDE2170, WDE4360 manual Glossary

Glossary WD Enterprise WDE2170/WDE4360

9.GLOSSARY

Active Termination - Works to control the impedance at the end of the SCSI bus by using a voltage regulator. This reduces the susceptibility of the bus to noise, particularly when cables are long or when many devices are connected to the bus. Because it is active, regulating the power that it gets from the interface card, active termination is more stable than passive termination.

Adaptive Caching - The drive determines the environment in which it’s being used and optimizes the way it handles commands and data.

Auto Park - Turning off the drive's power causes the WDE2170/WDE4360 drive to move the read/write heads to a safe non-data landing zone and locks them in place.

Average Read Seek Time - Equal to the total time of a test divided by 50,000 random length and random head seeks.

Block - Group of bytes handled, stored, and accessed as a logical data unit, such as an individual file record.

Buffer - Temporary data storage area that compensates for a difference in data transfer rates and/or data processing rates between sender and receiver.

Command Queuing - Feature that enables the drive to receive I/O processes from one or more initiators.

Command Reordering - Feature that allows the drive to reorder I/O processes in the command queue, thereby minimizing the seek time and rotational latency.

Correctable Error - Error that can be corrected by the use of Error Detection and Correction algorithms.

Customer Configuration Code (CCC) - Located on the product label attached to the drive. This code is revised only when changes affect the drive’s form, fit, or function.

Data Transfer Rate - Speed at which data transfers to and from the disk media (actual disk platter); a function of the recording frequency. Typical units are bits per second (bps) or bytes per second. Modern hard drives have an increasing range of disk transfer rates from the inner diameter to the outer diameter of the disk. This is called a “zoned” recording technique.

Defect Management - General methodology of eliminating data errors on a recording surface by mapping out known defects on the media.

Differential SCSI - Each signal consists of two lines called “–Signal” and “+Signal”.

Commands and data are carried over two sets of wires, and the difference is taken between each set of signals. Two-wire signaling is a proven way to achieve reliable signal transmission in noisy environments and over long distances.

ECC On-the-Fly- 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.

Embedded Servo Control - Design that generates accurate feedback information to the head position servo system without requiring a full data surface (which is required with a “dedicated” servo control design).

Error Correction Code - Mathematical algorithm that can detect and correct errors in a data field by adding check bits to the original data.

Error Rate - Number of errors of a given type that occur when reading a specified number of bits.

40 RELEASED 04-08-97 4079-001045 Rev. B