When I first began being interested in building my own computer, it was hard to understand the difference between different component standards. So I didn't really know what was best for my needs. This is especially true when dealing with storage. Currently, the two most popular hard drive interfaces are IDE/ATA and Small Computer Systems Interface, also known as SCSI. Both have their advantages and disadvantages. Most everyone that have tinkered with their PC has probably heard of these interfaces but most people know very little about the SCSI interface. When I started messing around with my computer, I had a basic concept of what IDE/ATA was and how it fit into the whole scheme of things. However, I only knew that SCSI existed but really didn't know much about it. I did know that it was expensive to implement.
It's not really just an interface, but more of a system level bus which makes it more advanced than IDE. It's similar to IDE in that you use a host adapter (controller) to connect a bunch of hard drives together. The difference is that each SCSI device works together with the system to manage the flow of data. SCSI is not just limited to hard drives but it can support all different types of devices. However, IDE is more commonly used because of the higher cost of SCSI. Also, the average user won't really benefit much from using SCSI. It's the higher end systems that benefit and use SCSI. Standardization has been a problem for both IDE/ATA and SCSI. It's always confusing to try to figure out what all the standards mean. This article will basically try to explain all the different types of SCSI standards and the features associated with them, as well as, look at the issues surrounding SCSI. Since there are many implementations of SCSI out there from various manufacturers, I'll try to look at SCSI in general. This is by no means a "How To" guide, but more of an explanation of the overall picture.
History of Small Computer Systems Interface (SCSI)
As I understand it, the first concepts of SCSI was thought up by Alan Shugart of Shugart Associates. He created a very early predecessor of SCSI, the Shugart Associates Systems Interface (SASI). Although it was very limited in its command set and capabilities, it was very revolutionary for its time. Shugart pushed to get SASI made into an ANSI standard, so it would be more widely used in the industry. Changes were made to the interface to improve it a bit, including the name change to SCSI. In 1986, the first SCSI standard was approved by ANSI. Since that first standard was approved, SCSI has evolved into the SCSI-2 and SCSI-3 standards. From the start, SCSI was designed to provide high level performance and expandability. In the next sections I'll try to explain the SCSI standards.