Typical Head Alignment Times; Command Queuing - HP C2488A Technical Reference Manual

Drive Automatic Mode Initiator Controlled Mode
State
(bit 6
=
0) (bit 6
=
1)
Norm4/ Perlonn no automatic head alignments. Disable automatic head alignments.
RezeroUnit behavior: Rezero Unit behavior:
bit 7 =0: align current head on next Rezero Unit bit 7
=
0: align current head on next Rezero Unit
command command
,
bit 7
=
1: align: all heads on next Rezero Unit bit 7 = 1: align all heads on next Rezero Unit
Command
--
Command
Needed: Embed single-head alignments in Seek, Read, and Disable automatic head alignments. Execute
Write commands. alignments upon receipt of Rezero commands.
Rezero Unit behavior: Rezero Unit behavior:
bit 7 = 0: align current head on next Rezero Unit bit 7 = 0: align current head on next Rezero Unit
command
command
bit 7 = 1: align all heads on next Rezero Unit bit 7 = 1: align all heads on next Rezero Unit
command command
CritiC4i: Write Protect until alignment occurs on next Seek, Disable automatic head alignments except for a write
Read, or Write command. to a head that needs alignment. Write Protect until
Rezero Unit behavior:
alignment occurs on next write.
bit 7
=
0: align current head on next Rezero Unit
Rezero Unit behavior:
command bit 7 = 0: align current head on next Rezero Unit
bit 7
=
1: align all heads on next Rezero Unit
command
command
bit 7 = 1: align all heads on next Rezero Unit
command
Typical Head Alignment Times
The time requirements for head alignments will vary according to how they are executed.
Some typical values are listed below:
Single Head Alignment: .................... 110 milliseconds
All-Heads Alignment:
13 data heads ................•..... ;.: .. 820 milliseconds
Command Queuing
The disk drives support the following SCSI command queuing operations:
• Head of Queue Tag. Instructs the Target to put the command that follows at the front of
the command queue and execute it immediately following the command currently being
executed. A command in the process of being executed will not be pre~empted. The Target
executes multiple Head-of-Queue commands in last-in, first-out order.
• Simple Queue Tag. Instructs the Target to put the command that follows at the end of the
command queue. The Target executes multiple Simple-Queue commands in any order that
will enable it to minimize actuator seek times to block locations if the queue algorithm
modifier allows it.
• Ordered Queue Tag. Instructs the Target to put the command that follows at the end of
the command queue. The Target executes Ordered-Queue commands in the order they were
received. All Simple-Queue commands received prior to an
Ordered~Queue
command are
3·4 Product Features
DRAFT
1/18/93 09:58