APPENDIX D
GLOSSARY
Actuator
An actuator positions the read/write heads
at
the desired cylinder. The Quantum actuator
consists
of
a rotary voice coil and the head mounting anns. One end
of
the head mounting
anns attach to the rotor with the read/write heads attached at the opposite end. As current
is
applied to the rotor, it rotates, positioning the heads over any cylinder on the surface.
Block
The SCSI interface uses logical blocks when transferring data across the bus. A block
of
data can be set equal to 512, 1024 or
~8
bytes.
Byte
This tenn indicates an 8-bit unit
of
infonnation.
Command
The sbucture
used
to
communicate requests from an initiator to a target.
Descriptor
Block
(CDB)
Connect
The function that occurs when an initiator selects a target to start an operation.
Cylinder
A set
of
tracks on multiple recording surfaces at anyone actuator position or location. The
ProDrive
40S and 80S have 834 data cylinders.
Data
Error
Any discrepancy between recorded and recovered
data
at the sector level.
See
Appendix
C.
Disconnect
The function that occurs when a target releases control
of
the SCSI bus, allowing it to go
to the BUS
FREE
phase.
Disk/Platter
A very flat circular substrate upon which a magnetic thin film is deposited or coated. Each
disk
has
two surfaces for recording infonnation.
Initiator
An SCSI device (usually a host system) that requests an operation to be perfonned by
another SCSI device.
Latency
Time
The period
of
time in which the read/write heads
are
waiting for
the
data to rotate into
position such that they can be accessed. Based on the disk rotating speed
of
3662
RPM,
the
maximum latency time is
16.4
milliseconds, and the average latency time
is
8.2
milliseconds.
Logical
unit
A physical
or
virtual device addressable through a target.
Logical
unit
An encoded three-bit identifier for
the
logical unit
Dumber
LSB
Least Significant Bit
L
UN
Logical Unit Number
m s Millisecond (10-
3
seconds)
MSB
Most Significant Bit
Media
The magnetic film that is deposited
or
coated on an aluminum substrate which is very flat
and in the shape
of
a disk.
The
media is overcoated to prevent damage to the heads or media
during head take off and landing.
f.1
s Microsecond
(10-6
seconds)
Appendix
0
Glossary
0-1
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