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A+
SCSI Tutorial
A+ Certification Essentials - SCSI Tutorial
The Small Computer Systems Interface (SCSI) is a bus interface and is in many ways more like an expansion bus than a drive adapter technology. SCSI, which is pronounced “skuzzy,” supports all sorts of data storage devices, printers, scanners, and video devices. SCSI has even been used as the basis for very high performance computer networks.
SCSI was developed in the early 1980's but not standardized by ANSI until 1986. Since that time, the technology has undergone many changes. It remains a popular drive interface with workstations, servers, and high-end desktop computers. It's also commonly used with higher-end scanners and digitizing devices. Until recently, SCSI was also very popular with drives used with MAC computers.
Device IDs
Every SCSI device, including the host bus adapter (HBA), must be assigned a unique ID number. SCSI IDs begin at 0 and count upward, with higher IDs having a higher priority on the SCSI bus. The HBA is normally assigned the highest SCSI ID. For example, with a SCSI Ultra-320 system, the HBA would be assigned ID 15.
You must assign devices a unique ID. It's not uncommon when implementing SCSI devices to have ID conflicts that prevent devices from working.
Termination
You must add terminating resistors to each endo fo the SCSI bus. These terminators are basically electrical resistors that serve to absorb signals that reach the end of the bus. Without them, signals could reflect back onto the bus, leading to a confusing mix of actual and reflected signals.
Typically, the HBA includes removable resistors. Modern devices have switch-selectable termination built in: if you need a device to provide termination then you switch on its terminators. Otherwise, you can leave its terminators turned off.
SCSI terminators are supposed to add electrical impedance equal to the impedance of the cable. Passive terminators are simply resistors that dampen reflected signals through non-electronic means. They will come close to matchng the impedance in most situations. In demanding applications, however, you should use an active terminator. An active terminator is an electronic component that dynamically tunes itself to match the impedances of the cable exactly. Active termination is most often used with the newer, higher performing SCSI types.
There are various training options for A+ certification. You can take self-paced learning methods such as A+ CBT training cd or study guides. If you need a class environment, you can take a A+ boot camp class. The one week training classes include an A+ certification guarantee!
If you have any questions, please call 1-866-718-7246.