The term 'magnetic media' is used to describe any record format where analogue or digital information is recorded to and retrieved from a coated matrix that can be magnetised.
Common types of magnetic media are:
- audio reel-to-reel and cassettes tapes
- video and computer tapes on open reels or in cassettes
- hard disk drives, (HDD)
- floppy disks or diskettes.
Magnetic tape has a plastic carrier coated with a matrix of metal or metal oxide particles, a resin binder and other ingredients such as lubricants and fungicides. Sometimes the tape has an antistatic coating on the back to reduce static charge build-up and to improve its winding capability.
Magnetic hard disks usually have an aluminium base, coated on both sides with a metal or metal oxide matrix. They have wide application in computing as the principle storage medium. Floppy disks and diskettes consist of a plastic base with a magnetic matrix on one or both sides. They are enclosed in a rigid, plastic protective jacket. Although an obsolete medium they are still likely to be found in collections and are a priority for transfer to new media.
Preservation and storage
All materials degrade at different rates over time. We cannot prevent this inevitable deterioration, but we can slow it down. Below are examples of the types of deterioration to which magnetic media are prone.
- Older acetate audio tapes can become brittle and easily broken. The magnetic coating on tapes and disks can deteriorate and subsequently flake off the base.
- Print-through, which is the transfer of a signal from one loop of tape onto an adjacent loop. This takes the form of a pre-echo and can be obviated by storing audio tapes 'tail-out' on their reels.
- High temperature and humidity and fluctuations may cause the magnetic and base layers in a reel of tape to separate, or cause adjacent loops to block together. High temperatures may also weaken the magnetic signal, and ultimately de-magnetise the magnetic layer.
- Tapes are particularly susceptible to mould because pockets of air trapped in the windings can create microclimates which will support mould growth.
- Dust, dirt, grease and chemical pollutants can promote moisture condensation and oxidative deterioration. These contaminants also interfere with the contact between the playback head and the tape, causing audio signal drop-outs.
Magnets or magnetic fields can cause information loss on a tape or disk if it is in close proximity for long enough because information is encoded on magnetic media by the alignment of magnetic particles. The degree of risk depends on a number of factors; proximity of the media to the source of the field; strength of the field, and duration of exposure. Running a vacuum cleaner past the shelves will probably not cause any damage, because magnetic effects decrease with distance.
- Always handle magnetic media as carefully as possible.
- Pick up magnetic tapes by their protective cases – do not touch the tape or disk surface.
- Wear lint-free gloves or ensure that hands are clean and dry.
- Support open-reel tapes by the hub during handling and transportation.
- Disks should never be flexed, bent or picked up by the oval slot in their jackets, or by the centre hole of the disk.
- Labelling should be in ink rather than pencil, as graphite dust from the pencil could interfere with the reading of the disk or tape. Once applied, labels should not be written on, and should only be attached to a protective case, rather than directly onto the magnetic tape or disk.
- Only remove items from their protective packaging for immediate use, and return them to their containers directly after use.
- Audio cassettes and open reel tapes should be wound to the end of one side after use and not left in a partly wound state for any length of time. Avoid use of the 'pause' mode with audio and video cassettes.
- When moving magnetic media ensure that it is properly packed in custom-made transportation canisters and is not bumped or dropped. Consult specialist freight and courier companies when transporting large quantities of magnetic media.
Magnetic media is sometimes supplied in cardboard enclosures. These can be used for the storage when in good condition. However, when they are older or damaged, they tend to generate dust.
Tapes should be stored in cases made of non-magnetisable material, preferably an inert plastic such as polypropylene. Cases should have internal lugs to securely hold the tapes by the hub. They should be strong enough to protect the cassettes from external damage and close tightly to keep out dust.
Reels or cores used for winding tapes should be clean and undamaged. Reels should be made of aluminium or a stable inert plastic.
Floppy disks and diskettes should be stored in protective envelopes that have a non-abrasive surface and are resistant to the build-up of static electricity. Tyvek envelopes are widely available and are suitable for this purpose.
Measures, such as the installation of an air-lock, or the maintenance of positive internal air pressure, can be taken to prevent dust entering from the outside.
Magnetic media should ideally be stored in closed metal cabinets to provide extra protection against heat and dust. However, if adequate environmental controls are in place, storage on open shelves, in their cases is acceptable. Storage equipment should be sturdy, allow tapes and disks to be stored vertically, and most importantly, be electrically grounded.
The National Archives provides a Standard for the Physical Storage of Commonwealth Records (pdf, 400kb) that recommends environmental conditions suitable for magnetic media.
Turn off lights in storage areas when not in use to minimise the exposure of records. An ideal storage area would have no windows, but if windows are present they should be covered with curtains or blinds.
Cleanliness is very important in storage areas, for reasons of records protection and, work health and safety. Never allow food or drink to be taken into a records storage area, and ensure the area is cleaned regularly. Insects and rodents, once attracted to a records storage area by food, may begin to eat the records. For further information the National Archives provides information on Integrated Pest Management.
The Archives Disaster Preparedness Manual for Commonwealth Agencies (pdf,429kb) offers specific advice for recovery of records.
It is essential that recording and replay equipment for magnetic tapes is maintained in good condition because information held on magnetic media is mechanically processed. Poorly maintained equipment can damage records. The heads, disk drive and tape drive elements of playback and recording equipment should be cleaned regularly in accordance with the manufacturers' recommendations.
To minimise deterioration due to handling and use, copies of important and frequently used tapes should be made for reference purposes. Ideally, a preservation master copy, a duplicating copy and a reference copy should be produced, and clearly labelled as such. As a disaster preparedness measure, the preservation master copy should be stored in a different location to the others. The duplicating copy may be used to produce further reference copies when required.
Long-term preservation of magnetic media is affected by two major factors; its intrinsic instability and the likelihood of the hardware obsolescence. The equipment used to access magnetic media today will almost certainly have been superseded in the next decades. For all practical purposes the records will be unusable, even media in good condition. The main prospect for long-term retention of the information held on magnetic media seems to be in regular copying or data migration, thus maintaining a good quality signal that can be read using available equipment. Copying can either be to fresh tape or disk, or to some other machine-readable format. Once copied to an uncompressed digital format the information can be copied without loss of quality.
Please contact the Agency Service Centre.