 DE
Disk enclosure, container of five
sub-assemblies :
- Fixed disks
- Spindle with integrated motor
- Actuator
- Heads
- Filtering system
Protection of the internal components from
environmental contaminants requires that the DE be sealed
at the source of manufacture and must not be opened. DE
is sometimes referred to as the head/disk assembly (HDA).
Dedicated Servo
Positioning method where servo information
is written on one disk surface only. This position
information is read and evaluated permanently. The linear
voice coil actuator and thus the read/write head is
tracked precisely.
Defect
Some irregularity in a medium which disturbs
its ability to carry recorded data. Defects in an optical
disk include bumps, depressions, dirt, missing sensitive
material, etc. Because of the high density of optical
recording, even micrometer size defects are important.
Defect (Pre-Write)
1. An area of the recording zone which when
read prior to any recording, yields an unexpected single
amplitude.
2. The ratio of the sum of the time intervals from the
beginning to the end of drop-ins on the disk to the total
available recording time on the disk.
Defect Distribution
The geographic distribution of errors on an
optical disk measured along its tracks and radially
across its tracks in terms of the occurrence of
successive n-bit errors. This concerns the media in both
an unrecorded and recorded state and does not address
focus or tracking servo defects.
Defect Management
A strategy whereby defective media areas
(e.g., sectors) that cannot be written due to hard
(uncorrectable) errors, are automatically assigned to
alternative areas which do not contain hard errors. The
strategy generally includes guidelines for disk rewrite
and disk retirement. Disk retirement is retention of a
disk which can be read but not written.
Defect Rate,
Initial
Average raw bit error rate of an optical
disk when writing and reading user data for the first
time.
Direct
Read After Write (DRAW)
A process in which data is read for
verification immediately after being written.
Direct
Read During Write. (DRDW)
Describes a method of error checking data on
an optical disk in which data is written and verified
during the same disk rotation. Refers to the ability to
read the information during the writing (recording)
process.
D List
SCSI Term. This list shows the positions of
defects as specified by the INIT using the FORMAT UNIT
command during disk initialisation.
DLC protocol (Data Link
Control).
A set of rules used by two nodes on a data link
to accomplish an orderly exchange of information.
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