6 | ST43401N/ND, ST43402ND User’s Manual, Rev. B |
When the drive is not powered on, the heads rest on the disc surface in a preassigned landing zone beyond the data zone. The actuator automatically latches in this position at shutdown for moving or shipping protection. When the drive is activated to bring the discs up to speed, the heads fly on a cushion of air close to the disc surface.
After arriving at the data track and selecting a head, the controller locates the portion of the track where the data is to be read or written. This is called track orientation. Signals from the drive indicate the beginning of each track. The controller uses these signals to determine the position of the head on the track.
When the head is above the desired track location, the controller commands the drive to actually read or write the data. During a read operation, the drive retrieves data from the discs, processes it, and transmits it to the controller. During a write operation, the drive receives data from the controller, processes it, and stores it on the discs.
The drive can recognize certain errors that may occur during its operation. When an error is detected, it is indicated to the initiator by the SCSI controller.
Initiator I/0 Lines
| Unit | Data recorded in | |
| concentric tracks | ||
| Selection | ||
|
|
| |
| Logic |
|
|
|
| Head |
|
|
| Selection | Heads |
|
| Logic |
|
SCSI |
|
|
|
Controller | Read/Write |
|
|
| Logic |
| Discs |
|
|
| |
| Seek |
|
|
| Logic |
|
|
| Track |
|
|
| Orientation |
|
|
| Logic |
|
|
| Error |
|
|
| Detection |
| Power Supply |
| Logic |
| |
|
|
| |