|An informational and technical guide to selecting the best hard drive for building a new computer or upgrading a current system.|
SCSI Hard Drive Technical Information
SCSI stands for Small Computer Systems Interface and is pronounced "scuzzy". SCSI drives offer high performance and large capacity suited for servers and high end workstations. Think of the interface as an intelligent stand-alone bus.
SCSI is an entirely different hard disk interface than the more common IDE. It is more of a system level interface, meaning that it does not only deal with disk drives. It is not a controller, like IDE, but a separate bus that is hooked to the system bus via a host adapter. A single SCSI bus can hold up to eight units, each with a different SCSI ID, ranging from 0 to 7. The host adapter takes up one ID, leaving 7 ID's for other hardware. Typical SCSI hardware includes hard drives, tape drives, CD-R/RW drives, scanners, etc.
SCSI Hard Drive Popularity is Increasing
SCSI's popularity is increasing. Speed seems to be the main reason for this, although this may not really be too anything to get excited about as will be discussed a little later. One advantage is that there are a multitude of hardware types that can use a SCSI bus. The interface is very expandable, whereas IDE is pretty much limited to hard drives and CD-ROMs.
The reason for the slow acceptance of SCSI is the lack of standard. Each company seems to have its own idea of how SCSI should work. While the connections themselves are relatively standardized, the actual driver specs used for communication have not been. The end result is that each piece of SCSI hardware has its own host adapter, and the software drivers for the device cannot work with an adapter made by someone else. So, due to the lack of an adapter standard, a standardized software interface, and a standard BIOS for hard drives attached to the SCSI adapter, SCSI can be sometimes puzzling for the end-user. Even so, SCSI is a relatively easy thing to implement, should you wish to.
The SCSI Hard Drive Interface Evolution
SCSI has come a long way. In the beginning, one couldn't even use a hard drive on the bus. This was mainly because the BIOS in those systems were designed to use the ST506/412 controller. With the IDE, the BIOS was easily changed because of the similarity to ST506/412 on the WD1003 controller. At the register level, though, SCSI was very different, and would have required an entirely new set of BIOS in the PC. Newer PC BIOS versions have been designed with built-in SCSI support, but this is not always included on a motherboard. If not, there is an extension BIOS on the host adapter. Many high-end systems have built-in SCSI support. There is usually an adapter card or an adapter built-in to the motherboard. This native support for SCSI was set in motion by IBM. Their example was followed by many manufacturers. As a result, SCSI integration is becoming easier to work with and will get easier as technology progresses.
The SCSI Interface Standards
There is more than one version of SCSI out there: