Hard Drive Interface Standards
There are several interface standards for passing data between a hard disk and a computer. The most common are the SCSI or Small Computer System Interface, the standard interface for Apple Macs; the IDE or Integrated Drive Interface, which is not as fast as SCSI; and the Enhanced IDE interface, which is a new version of the IDE interface that supports data transfer rates comparable to SCSI.
IDE Drives
The Integrated Drive Electronics interface was designed for mass storage devices, in which the controller is integrated into the disk or CD-ROM drive. It is thereby a lower cost alternative to SCSI interfaces in which the interface handling is separate from the drive electronics. The original IDE interface supports data transfer rates of about 3.3 Mbytes per second and has a limit of 538 Mbytes per device. However, a recent version of IDE, called enhanced IDE (EIDE) or Fast IDE, supports data transfer rates of about 12 Mbytes per second and storage devices of up to 8.4 Gbytes. These numbers are comparable to what SCSI offers. However, because the interface handling is handled by the disk drive, IDE is a very simple interface and does not exist as an interequipment standard, that is, you cannot connect an external drive using IDE. Due to demands for easily upgradable storage capacity, and for connection with external devices such as recordable CD players, SCSI has become the preferred bus standard in audio applications.
SCSI
An abbreviation of Small Computer System Interface and pronounced “scuzzy,” SCSI is a parallel interface standard used by Apple Macintosh computers (and some PCs) for attaching peripheral devices to computers. All Apple Macintosh computers starting with the Macintosh Plus come with a SCSI port for attaching devices such as disk drives and printers. SCSI interfaces provide for fast data transmission rates,; up to 40 Mbytes per second. In addition, SCSI is a multidrop interface, which means that you can attach many devices to a single SCSI port.
Although SCSI is an ANSI standard, unfortunately, due to ever higher demands on throughput, SCSI comes in a variety of “flavors!” Each is used in various studio and mastering applications and, as a musician engineer, you will need to be aware of the differences. The following varieties of SCSI are currently implemented:
SCSI-1: Uses an 8-bit bus and supports data rates of 4 Mbytes/s.
SCSI-2: Same as SCSI-1, but uses a 50-pin connector instead of a 25-pin connector. This is what most people mean when they refer to plain SCSI.
Fast SCSI: Uses an 8-bit bus and supports data rates of 10 Mbytes/s. Ultra SCSI: Uses an 8-bit bus and supports data rates of 20 Mbytes/s.
Fast Wide SCSI: Uses a 16-bit bus and supports data rates of 20 Mbytes/s.
Ultra Wide SCSI: Uses a 16-bit bus and supports data rates of 40 Mbytes/s; this is also called SCSI-3.
Fiber Channel
Fiber channel is a data transfer architecture developed by a consortium of computer and mass storage device manufacturers. The most prominent Fibre Channel standard is Fibre
Channel Arbitrated Loop (FC-AL), which was designed for new mass storage devices and other peripheral devices that require very high bandwidth. Using an optical fiber to connect devices, FC-AL supports full-duplex data transfer rates of 100 Mbit/s. This is far too high a transfer rate to be relevant as an audio-only standard. However, in multichannel applications and in multimedia applications (with video, for example) Fibre Channel may well find its way into the modern studio, so much so that FC-AL is expected to eventually replace SCSI for high-performance storage systems.
Firewire (IEEE 1394) Interface
The “Firewire” (IEEE 1394 interface) is an international standard, low-cost digital interface intended to integrate entertainment, communication, and computing electronics into consumer multimedia. Originated by Apple Computer as a desktop LAN, Firewire has been developed by the IEEE 1394 working group. Firewire supports 63 devices on
a single bus (SCSI supports 7, SCSI Wide supports 15) and allows buses to be bridged (joined together) to give a theoretical maximum of thousands of devices. It uses a thin, easy to handle cable that can stretch further between devices than SCSI, which only supports a maximum “chain” length of 7 meters (20 feet). Firewire supports 64-bit addressing with automatic address selection and has been designed from the ground up as a “plug and play” interface. Firewire can handle 10 Mbytes per second of continuous data with improvements in the design promising continuous throughput of 20–40 Mbytes per second in the very near future and a long-term potential of over 100 Mbytes/s. Much like LANs and WANs, IEEE 1394 is defined by the high-level application interfaces that use it, not a single physical implementation. Therefore, as new silicon technologies allow
high higher speeds and longer distances, IEEE 1394 will scale to enable new applications.