The A+ Certification & PC Repair Handbook (Charles River Media Networking/Security)

As mentioned in Chapter 20, SCSI interfaces can be attached internally or externally to a computer system. For example, an SCSI hard drive can be attached to an internal SCSI controller on the motherboard. A device such as an SCSI printer or SCSI CD-ROM can be connected to an external SCSI controller card that extends out of the back of a computer. The devices that attach to SCSI controller cards have SCSI interfaces built onto them. There are internal and external SCSI connectors that reflect the SCSI standard being implemented on the device or controller. The most common SCSI interface connectors in use today are 50-pin and 68-pin SCSI internal and external SCSI connectors, as well as the 80-pin internal SCSI SCA connector. Devices such as printers and CD-ROMs utilize an SCSI 50-pin or 68-pin cable and connectors. SCSI SCA 80-pin connectors are used for hot-swappable hard drives, most commonly with internal RAID (Redundant Array of Independent Disks, or Redundant Array of Inexpensive Disks) configurations. The SCA SCSI adapter card includes a built-in power connection to support its special voltage requirements. Figure 21.7 shows the basic SCSI connectors and SCSI pin configurations. Remember, the exam will most likely focus on the 50-pin or 68-pin SCSI cable.

Figure 21.7: Basic SCSI connectors and their pin configurations.

Here are several useful tips to remember about SCSI technology and interfaces:

• Most SCSI cables are 50-pin.

• SCSI Wide refers to a 68-pin parallel interface cable.

• SCSI-3 is considered ultra-wide and can support up to 16 devices, including the controller card.

• SCSI-3 is backward compatible with previous forms of SCSI technology.

• Each SCSI device must have a unique SCSI ID.

• A SCSI chain must be terminated at both ends.

• You cannot network two computers together with an SCSI cable.