IntroductionSCSI (Small Computer System Interface) is high end technology. It is a technology which provide means for data exchange among hardware devices such as drives, tape streamers and scanners. SCSI is especially used in high end PCs such as network servers or just powerful workstations.
SCSI might be compared to the EIDE interface, which also uses a host adapter controlling drives. However SCSI has two major advantages over EIDE:
A SCSI system is built around a central, intelligent controller called the host adapter . A host adapter can control several SCSI units:
The host adapter has its own BIOS separate from the PC's. When you boot the PC, you will see the adapter communicating with connected SCSI devices.
The adapter is rather expensive. Currently, the best for ordinary use is called Adaptec 2940 U2W (priced at around $200). It is PCI based, so you could use it in your next PC too. I have had good experiences with ASUS motherboards in versions with onboard SCSI controller. That is the most easy solution - to have the controller onboard.
The regular SCSI 2 system can handle 8 devices including the adapter itself. SCSI Wide handles 15 devices. Each device has to be assigned a unique number going from ID 0 to ID 7. The SCSI devices can be internal (installed inside the PC cabinet) or external . The host adapter is a device itself. Typically, the host adapter will occupy ID 7.
Here is an illustration of a SCSI string with host adapter (ID 7) and
five units (ID numbers 0, 1, 2, 4, and 5):
Terminators in both endsThe last unit in both ends of the SCSI chain must be terminated. This means that there must be resistors (jumpers or switches) attached to two of the units.
If you only use two devices, you do not have to worry about it. The host adapter is one end of the chain and the other device is the other end. With three or more units you have to take care of termination:
Read about FireWire in module 5c3
Read about chip sets on the motherboard in module 2d
Read Module 4d about super diskette and MO drives.
Read module 5a about expansion cards, where we evaluate the I/O buses from the port side.
Read module 5b about AGP
Copyright (c) 1996-2005 by Michael B. Karbo. www.karbosguide.com.