Chapter 20 - Drive Interface

Abstract

For the disk drive to provide its data storage service to a host, it needs to have a protocol established to receive I/O commands from the host and to signal back to the host their completions. This chapter discusses the most common standard interfaces in use today. It opens up with a general overview of interfaces, followed by high-level descriptions of the major characteristics and features of five different interface standards. It discusses disk drive's cost, performance, and reliability with respect to its interface. The interface is the communication channel over which I/O requests are sent from the host to the disk drive and through which all data transfers for reading and writing take place. Common to all standard interfaces, when an I/O request is issued to a disk drive, three basic parameters are needed before the drive knows what to do: whether the command is for a read or a write operation, the starting address for the command, and the number of sectors of data to be read or written. When the drive has finished performing an I/O request, regardless of which standard interface is being used, the drive needs to inform the host of this completion. There are several common standard interfaces for disk drives today. They are the parallel and serial versions of ATA, parallel and serial versions of SCSI, and the serial Fiber Channel. SCSI and FC disk drives cost significantly more, have higher performance, and are more reliable than ATA drives.