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[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk Interfaces and Configuration | Small Computer Systems Interface (SCSI) | SCSI Data Transfer Modes and Feature Sets ]
SCSI Transfer Mode and Feature Set Compatibility
I sometimes call the various types of SCSI "flavors"; well, if that's so, the way the interface is heading we'll soon be in Baskin Robbins territory. ;^) The sheer number of different kinds of SCSI can certainly make the interface seem overwhelming! How does a SCSI user make it all of this hardware work together? Fortunately, while the standards and feature sets can be quite confusing, the hardware is actually well-engineered, and the standards are designed to allow different hardware types to work together fairly readily.
It's important to remember that a key design goal of all SCSI standards is backwards compatibility. Few people want to buy new hardware that won't work with their older hardware. Therefore, in most cases, at least in theory, you can mix older, slower hardware with newer, faster hardware. You can, again in theory, put a brand-new Ultra160 SCSI hard disk on the same SCSI bus with a decade-old SCSI-1 host adapter (albeit with added hardware and suboptimal results.) This is generally true, but note the important qualifier: in theory. Since changes are always being made to the signaling and other aspects of the interface, there is no guarantee that any two very different pieces of SCSI hardware will work together.
There are no hard and fast rules regarding the compatibility of different SCSI transfer modes and feature sets, especially if they are very different in terms of key attributes. Here are some issues that you should keep in mind as you consider device compatibility: