Seagate ST43400N/ND user manual Drive functional block diagram

General description 5

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

Figure 2. Drive functional block diagram

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 also recognize certain errors that may occur during its operation. When an error is detected, it is indicated to the initiator by the SCSI controller.