Scsi Pointers - Seagate ST11200 Product Manual

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E 23
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3.4

SCSI pointers

The disc drive supports systems that use the pointer philosophy described in the following paragraphs.
Consider the system shown in Figure 3.4-1 in which an initiator and target communicate on the SCSI bus in
order to execute a command.
Initiator Target
Function Function
Path Path
SCSI
Origin Execution
Control Control
Bus
Initiator Target
Figure 3.4-1. Simplified SCSI system
The SCSI architecture provides for sets of pointers to be kept within each initiator Path Control area (see
Figure 3.4-1). These pointers are in sets of three pointers per set. The pointers in each set point to three
storage area sections in the initiator. The three sections contain the following information:
1. A command from initiator to target.
2. Status (from target) associated with the command.
3. Data (to/from target) associated with the command.
Of these three-pointer sets there are two types:
1. Current (active) pointers (one set per initiator only).
2. Saved pointers (one or more sets per initiator, up to seven sets total).
The use of these two types of pointers is described in the following paragraphs.