Chapter 5. Managing Storage

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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. Interfaces are important 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 orga 

nization'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 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 used on minicomputers of the 1970s.

SMD

A successor to IPI, SMD (stands for Storage Module Device) was used on 8 and 14 inch mini 

computer 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.