The FDS is a five-level classification system for describing the current practical status of obsolete, discontinued, and legacy computer and electronic storage formats. It is intended to measure how readily a format can still be used today, taking into account the availability of new and used media, compatible readers and drives, manufacturer support, and the difficulty of obtaining functioning equipment.

The scale ranges from Active, describing formats that remain in current production, to Extinct, describing formats for which usable media and reading equipment are effectively unavailable. The scale measures the practical accessibility of a format rather than simply its age or whether its original manufacturer still exists.

A format's classification may change over time. A discontinued format may initially remain Supported or Obsolete while large quantities of media and hardware remain available, but eventually progress to Endangered as equipment becomes scarce and existing hardware fails. Conversely, the discovery of surviving equipment, the development of new interfaces, or the manufacture of replacement hardware can make an otherwise obsolete format significantly easier to access.

The scale describes the format as a whole rather than the condition of any particular piece of media. Individual examples may be considerably easier or harder to use than the classification suggests.

In Production. Active formats that are currently manufactured and commercially supported. New media is being produced and sold, and compatible readers, drives, or other necessary hardware are readily available. The format may be in widespread use or may serve a specialized modern market; current production is the defining characteristic.

An Active format does not necessarily have to be technologically modern or popular. A format can remain at this level as long as new media and compatible equipment continue to be manufactured and are reasonably obtainable. Examples might include contemporary removable storage formats, optical media that remain in production, or specialized recording formats still used in some industries.

Discontinued but Supported. Supported formats are no longer being manufactured, but remain practical to use as compatible media and equipment are still commercially available. Manufacturers, vendors, or other organizations may continue to provide some degree of support, replacement equipment, accessories, or compatibility.

At this stage, obtaining and using the format generally requires little specialized knowledge. New-old-stock or previously manufactured media may still be widely available, and working readers or drives can be commonly purchased. The format is no longer actively produced, but its existing ecosystem remains sufficiently intact for ordinary use.

Discontinued but Obtainable. Obsolete formats are no longer in production and generally no longer receive meaningful manufacturer support, but their media and reading equipment remain reasonably obtainable. Most surviving examples are found through second-hand markets, specialist suppliers, surplus equipment dealers, collectors, or other sources rather than ordinary retail channels.

Using an Obsolete format may require some additional effort compared with a Supported format, but it is generally still practical for an individual or organization with sufficient interest. Working drives and readers can usually be found without going to extreme lengths, although prices and availability may vary considerably. This level represents formats that have clearly passed out of mainstream use but remain accessible through their surviving hardware and media.

Difficult to Use. Endangered formats remain technically usable, but obtaining the necessary media or equipment has become difficult, expensive, or unreliable. Working readers and drives may exist only in small numbers, while replacement parts and compatible accessories may be scarce. Specialized adapters, donor hardware, maintenance, or technical expertise may be necessary to operate the format.

At this stage, preservation becomes increasingly dependent on the continued survival of individual pieces of equipment. A format may have plenty of surviving media but very few functioning readers, or functioning readers may exist while usable media is extremely difficult to locate. Data recovery and preservation projects involving Endangered formats may require specialist knowledge, repair work, or equipment maintained by collectors, archives, museums, or specialized recovery services.

Practically Unrecoverable. Extinct formats have reached the point where practical access to them is no longer generally possible. Usable media, compatible readers, or both are extremely rare, unavailable, or effectively unfindable. Surviving examples may exist in private collections, institutional archives, or unknown locations, but there is no dependable way for an ordinary user to obtain the equipment necessary to access the format.

Recovering data from a Extinct format may require custom-built hardware, reverse engineering, specialist archival facilities, reconstruction of obsolete / damaged equipment, or the discovery of previously unknown surviving hardware. In some cases, the format may be considered effectively inaccessible even though individual examples of its media or hardware are known to survive.

“Extinct” does not necessarily mean that no physical examples exist. Rather, it indicates that the format has ceased to be practically accessible as a usable storage medium. A single surviving drive in an archive, for example, does not make a format readily usable if there is no realistic way for others to obtain or operate such a drive.

The scale should be applied based on the current practical availability of the format, rather than its historical popularity, age, or technological sophistication. When assigning a level, consideration should be given to several factors:

• Media availability: How readily can usable blank or recorded media be obtained?
• Reader/drive availability: How readily can functioning hardware capable of reading the format be obtained?
• Hardware condition: Are surviving readers generally usable, or do they commonly require repair or maintenance?
• Interface compatibility: Can the hardware be connected to modern computers and equipment without specialized conversion?
• Manufacturer support: Does any manufacturer or vendor still provide support, parts, or replacement equipment?
• Cost and effort: How much time, money, and specialist knowledge are normally required to use the format?
• Specialist availability: Can the format still be accessed through archives, museums, collectors, or specialist recovery services?

The scale is deliberately based on practical accessibility rather than absolute extinction. A format should not be classified as Extinct merely because its manufacturer has disappeared or because no new hardware has been produced for many years. Likewise, the existence of a handful of surviving examples does not necessarily prevent a format from being classified as Extinct.

As a general rule, the scale describes the experience of someone attempting to obtain, read, or write the format today, rather than simply documenting whether examples are known to survive.