SCSIHD Configuration-SCSIID Select Termination Enable Disable
| Field | Computers |
| Went Obsolete | 2006 |
| Made Obsolete By | Serial Attached SCSI and Serial ATA |
| Knowledge Assumed | Binary counting |
| When useful | Working on high end servers, workstations, and early Macintosh computers |
SCSI (Small Computer System Interface) allowed for large amounts of data to flow quickly. In order to identify the devices attached to the parallel SCSI bus, devices had an ID. This ID was usually managed by a set of pins or a counter. The counter allowed you to press up and down buttons to set the value between 0 and 7. With pins, the user had to install jumpers to make the value of the three pairs of pins equal the desired SCSI ID. This was done in binary with each pair counting as a bit.
0 (000) 1 (001) 2 (010) 3 (011) 4 (100) 5 (101) 6 (110) 7 (111)
The SCSI chain had to be terminated at both ends to ensure data reliability. Most systems would not function at all without proper termination. Some devices, including most SCSI controller cards, had a set of resistors that could be enabled if that device was to be the last one in the chain. Sometimes, terminator devices were used. This was common with external devices as a block of resistors in a module that attached to the outbound port of the device.
SCSI has been mostly replaced today by Serial ATA and Serial Attached SCSI. Both are much faster than older style SCSI devices. SCSI was intended to be a low cost method for accessing high performance disks. It never became widely popular in the consumer computer market. It was commonly used in servers and high end workstations. Apple used SCSI drives in their early Macintosh computers, but that contributed to higher prices than their competitors. They were discontinued in favor of IDE drives, which PC manufacturers had been using since MFM hard drives became obsolete.
