Hard Disk Interfaces

by Phil Barker

Your computer hard disk is where data and programs are stored. The "interface" of a hard disk to the system can be defined as a boundary where connections from two or more independent and unrelated systems converge.

The most popular interfaces today are Enhanced IDE and SCSI. Each has its advantages. In essence, EIDE is used as a low cost storage medium for capacities up to 8.4 gigabytes and can support CD-ROM and a tape drive. The most popular EIDE standard today is the Fast ATA-2 PIO Mode 4. The ALLIANCE Pentium computers BIOS support and take advantage this mode.

The biggest advantage EIDE has over SCSI is a lower initial investment. The lower price makes these EIDE drives the most popular for desktop and mobile computing.

However, when operating in a high performance and demanding application environment use a SCSI interface and SCSI hard disk device(s).

SCSI is an intelligent interface that hides the devices physical format from the computers processor. This means you can mix and match devices on one controller, instead of requiring a separate controller for each device.

SCSI can take on multiple requests and reorder them so they can be processed most efficiently. Whereas EIDE must act on requests in the order in which they’re received.

SCSI has evolved from SCSI-I, to II to SCSI Wide and SCSI Fast/Wide. Data transfers can be up to 20MB/second. Up to 15 devices can be attached using SCSI Wide.

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