5.3. Mass Storage Device Interfaces
Every device used in a computer system must have some means of attaching to that computer system. This attachment point is known as an interface. Mass storage devices are no different -- they have interfaces too. It is important to know about interfaces for two main reasons:
- There are many different (mostly incompatible) interfaces
- Different interfaces have different performance and price characteristics
Unfortunately, there is no single universal device interface and not even a single mass storage device interface. Therefore, system administrators must be aware of the interface(s) supported by their organization's systems. Otherwise, there is a real risk of purchasing the wrong hardware when a system upgrade is planned.
Different interfaces have different performance capabilities, making some interfaces more suitable for certain environments than others. For example, interfaces capable of supporting high-speed devices are more suitable for server environments, while slower interfaces would be sufficient for light desktop usage. Such differences in performance also lead to differences in price, meaning that -- as always -- you get what you pay for. High-performance computing does not come cheaply.
5.3.1. Historical Background
Over the years there have been many different interfaces created for mass storage devices. Some have fallen by the wayside, and some are still in use today. However, the following list is provided to give an idea of the scope of interface development over the past thirty years and to provide perspective on the interfaces in use today.
- FD-400
- An interface originally designed for the original 8-inch floppy disk drives in the mid-70s. Used a 44-conductor cable with an circuit board edge connector that supplied both power and data.
- SA-400
- Another floppy disk drive interface (this time originally developed in the late-70s for the then-new 5.25 inch floppy drive). Used a 34-conductor cable with a standard socket connector. A slightly modified version of this interface is still used today for 5.25 inch floppy and 3.5 inch diskette drives.
- IPI
- Standing for Intelligent Peripheral Interface, this interface was used on the 8 and 14-inch disk drives deployed on minicomputers of the 1970s.
- SMD
- A successor to IPI, SMD (stands for Storage Module Device) was used on 8 and 14-inch minicomputer hard drives in the 70s and 80s.
- ST506/412
- A hard drive interface dating from the early 80s. Used in many personal computers of the day, this interface used two cables -- one 34-conductor and one 20-conductor.
- ESDI
- Standing for Enhanced Small Device Interface, this interface was considered a successor to ST506/412 with faster transfer rates and larger supported drive sizes. Dating from the mid-80s, ESDI used the same two-cable connection scheme of its predecessor.
There were also proprietary interfaces from the larger computer vendors of the day (IBM and DEC, primarily). The intent behind the creation of these interfaces was to attempt to protect the extremely lucrative peripherals business for their computers. However, due to their proprietary nature, the devices compatible with these interfaces were more expensive than equivalent non-proprietary devices. Because of this, these interfaces failed to achieve any long-term popularity.
While proprietary interfaces have largely disappeared, and the interfaces described at the start of this section no longer have much (if any) market share, it is important to know about these no-longer-used interfaces, as they prove one point -- nothing in the computer industry remains constant for long. Therefore, always be on the lookout for new interface technologies; one day you might find that one of them may prove to be a better match for your needs than the more traditional offerings you currently use.
