5.3.2. Present-Day Industry-Standard Interfaces
Unlike the proprietary interfaces mentioned in the previous section, some interfaces were more widely adopted, and turned into industry standards. Two interfaces in particular have made this transition and are at the heart of today's storage industry:
- IDE/ATA
- SCSI
5.3.2.1. IDE/ATA
IDE stands for Integrated Drive Electronics. This interface originated in the late 80s, and uses a 40-pin connector.
Note
Actually, the proper name for this interface is the "AT Attachment" interface (or ATA), but use of the term "IDE" (which actually refers to an ATA-compatible mass storage device) is still used to some extent. However, the remainder of this section uses the interface's proper name -- ATA.
ATA implements a bus topology, with each bus supporting two mass storage devices. These two devices are known as the master and the slave. These terms are misleading, as it implies some sort of relationship between the devices; that is not the case. The selection of which device is the master and which is the slave is normally selected through the use of jumper blocks on each device.
Note
A more recent innovation is the introduction of cable select capabilities to ATA. This innovation requires the use of a special cable, an ATA controller, and mass storage devices that support cable select (normally through a "cable select" jumper setting). When properly configured, cable select eliminates the need to change jumpers when moving devices; instead, the device's position on the ATA cable denotes whether it is master or slave.
A variation of this interface illustrates the unique ways in which technologies can be mixed and also introduces our next industry-standard interface. ATAPI is a variation of the ATA interface and stands for AT Attachment Packet Interface. Used primarily by CD-ROM drives, ATAPI adheres to the electrical and mechanical aspects of the ATA interface but uses the communication protocol from the next interface discussed -- SCSI.
