Slide 4 of 30
Notes:
A disk drive consists of one or more metallic platters stacked on a single spindle.
The typical sizes for disk drives these days are 5.25 and 3.5 inches. More data can be stored on a single 5.25 inch platter than on a 3.5 inch platter.
Typical spin rates for these platters is now 7200 rpm. Many drives are still at slower rates, such as 5400 and 4500 rpm. The fastest rotational speed in a production disk drive today is 10,000 rpm.
The actuator is the mechanism that moves the disk’s read/write heads over the recording surface of the platters. It performs the so-called seek function, and moves the heads to the desired “cylinder” or track where the heads will proceed to read or write information.
Disk drives have cache memories to improve throughput. Data movement to and from the storage medium can occur in bursts. Disk drives typically read more data from the platters than requested, storing the remainder in this cache in the hopes that it will soon be requested by the host computer.
Data to and from the host computer over the SCSI bus also occurs in bursts. If the disk drive has been told that it must flush its data to the platters before responding to the host that a SCSI write command is successful, then it is said that the disk’s write cache is disabled.
