SCSI

Small Computer System Interface (also known as SCSI, skuz-ee) is a parallel interface standard pioneered by Larry Boucher of Shugart Associates and later Adaptec.

History
The SCSI interface was first adopted by Apple Computer with the Macintosh Plus and was carried over into the early beige Power Macintosh line. Internal drives used a 50-pin IDC connector while external drives were connected with a DB-25 or a Centronics CN-50 connector.

Features
SCSI drives can be daisy-chained, but identities need to be manually set by jumpers or a switch to avoid SCSI ID collisions, which could render the entire chain inoperable. Lack of proper termination can also cause "SCSI voodoo". Utilities such as SCSI Probe and FWB Hard Disk Toolkit are useful in diagnosing the SCSI devices.

SCSI IDs
The following are typical or recommended assignments for SCSI IDs, though all except #7 (the host computer) can be re-assigned. The SCSI controller typically starts from the lowest ID when first searching for bootable drives:
 * 0: Boot drive
 * 1:
 * 2:
 * 3: CD-ROM drive
 * 4: SyQuest drive
 * 5: Zip drive
 * 6: Scanners or tape drive
 * 7: Host computer

Discontinuation
SCSI and several other legacy technologies were eventually phased out by Apple, starting with Steve Jobs' introduction of the iMac G3 in May 1998. As SCSI drives have become hard to find for replacement in vintage Macs, a SCSI2SD adapter can allow the use of a Secure Digital (SD) card in place of a hard disk drive.