The ATA (IDE) Interface

The interface used to connect a hard disk drive to a modern PC is typically called IDE (Integrated Drive Electronics) . However, the true name of the interface is ATA ( AT Attachment) . ATA refers to the fact that this interface originally was designed to connect a combined drive and controller directly to the bus of the 1984 vintage IBM AT (Advanced Technology) computer, otherwise known as the ISA (Industry Standard Architecture) or AT bus . IDE is a term originated by the marketing departments of some drive manufacturers to describe the drive/controller combination used in drives with the ATA interface. Integrated Drive Electronics refers to the fact that the interface electronics or controller is built in to the drive and is not a separate board, as with earlier drive interfaces.

Today, ATA is used to connect not only hard disks but also CD and DVD drives, high-capacity SuperDisk floppy drives, and tape drives. Even so, ATA is still thought of primarily as a hard disk interface, and it evolved directly from the separate controller and hard drive interfaces that were used prior to ATA. This chapter covers the ATA interface in detail, as well as the original interfaces from which ATA evolved. Because the ATA interface is directly integrated into virtually all motherboard chipsets, ATA is the primary storage interface used by most PCs, including both desktops and portables.

ATA is a 16-bit parallel interface, meaning that 16 bits are transmitted simultaneously down the interface cable. A new interface, called S erial ATA , was officially introduced in late 2000 and is being adopted in desktop systems starting in 2003 (it will likely be another year or so before it arrives in portables). Serial ATA (SATA) sends 1 bit down the cable at a time, enabling thinner and smaller cables to be used, as well as providing higher performance due to the higher cycling speeds allowed. SATA is a completely new and updated physical interface design, while remaining compatible on the software level with Parallel ATA. Throughout this book, ATA refers to the parallel version, whereas Serial ATA is explicitly referenced as SATA .

Note

Many people who use systems with ATA connectors on the motherboard believe that a hard disk controller is built in to their motherboards, but in a technical sense the controller is actually in the drive. Although the integrated ATA ports on a motherboard often are referred to as controllers , they are more accurately called host adapters (although you'll rarely hear this term). A host adapter can be thought of as a device that connects a controller to a bus.

The primary advantage of ATA drives over the older, separate controller “based interfaces and newer host bus interface alternatives, such as SCSI and IEEE 1394 (i.LINK or FireWire), is cost. Because the separate controller or host adapter is eliminated and the cable connections are simplified, ATA drives cost much less than a standard controller and drive combination.