Care and Handling of Magnetic Material
The stability of recorded information in magnetic media is vulnerable to damage due to its inherent magnetic nature as well as due to various external conditions and events. Inadvertent erasure can lead to loss of vital information. Inter-layer transfer and wear can effect the usability of the media. Similarly, careless handling and improper storage would damage recorded information. There should always be 2 copies of magnetic media-one storage copy and the other working copy. Information content of hard disks should also be kept as backup. The following are some points on storage and care of magnetic media requiring proper implementation:
The magnetic media storage area should be properly air conditioned with a temperature of 17-20° Celsius and relative humidity ranging from 35-45 per cent. The temperature and humidity should be constantly maintained round the clock.
Magnetic tapes should be enclosed in polyethylene bags. Similarly audio and video cassettes should be kept in plastic containers.
The storage area should be dust-free, as very small dust particle can make portion of magnetic media unreadable.
Storage area must be cleaned using vacuum cleaner.
Magnetic tapes and diskettes should be shelved in the upright, vertical position and should not be stacked horizontally.
Magnetic media should be handled gently. Information recorded space of the media should not be touched as finger prints, skin oils etc. may damage information.
Eating, drinking and smoking should be prohibited in the storage area. Boiling of water or otherwise creation of water vapour should also be prohibited in the storage area.
Magnets should be strictly prohibited in the storage as well as working area of magnetic media. While in transit at least 3" should be maintained between magnetic media and external magnetic fields.
Direct sunlight must be avoided to fall upon magnetic media.
Keep the magnetic media inside their container, while not in use.
Do not write directly on a diskette. Use previously prepared adhesive label. Use write protect tabs, to prevent the inadvertent over-writing or deletion of information recorded on floppy disks.
Equipments that are used in utilising magnetic media should be properly handled.
Magnetic media should be subjected to periodic rewinding to avoid accumulated stress on tapes for long term storage.
Periodic checking of magnetic media should be done for corrective measures. For longer life of magnetic media, periodic copying on to new media at regular interval is recommended. However, in case of audio and video cassettes, this may result in loss of image and or sound quality.
Library Magnetic Materials
Magnetic storage media serve broadly three information management applications, viz. i) data storage;
ii) Audio recording; and
iii) Video recording.
The data storage group of magnetic media is used by the computers, while the other two categories are used by specialised instruments, like audio record-player, video cassette player, etc. This category of materials are available in the form of tapes (sound and video) and discs.
Tapes
Tapes are made of a polyester base to which oxides of iron and chromium are attached. By magnetisation and rearrangement of the magnetic fields borne by these oxides, a message is recorded on the tape. This message (whether sound or video) can be 'read' by a device in the playback machine. Magnetic tapes used for data storage are read by special drives attached with the computers. Magnetic tapes: Magnetic tapes are the oldest of all magnetic media. The magnetic tapes vary in width from 4mm to 0.5 inches. It may be packed on open reels, in cartridges or cassettes of various size and shape. The commonly used open reel tape measures 10.5 inches in diameter and contain 2,400 feet of tape. Thinner tapes are also available with more footage of tape in the same 10.5 diameter reel. The storage capacity varies with linear recording density measured in bytes per inch. Depending on the recording density tapes are available, that can store 150 megabytes to 1.35 gigabytes of data. The IBM 3480 magnetic tape cartridge introduced in 1984 is a convenient and compact medium that records data on a half inch magnetic tape storing 200 megabytes of data in, 540 feet space. The cartridge measures, 4" x 5" x 1" size. Digital Audio Tape (DAT) is now being used to store backup data from servers and computers. They are comparatively small in size having a dimension of 7.2 x 5.4 x 1 cm. and width of 3.8 mm. They come in the form of cartridges.
Audio tapes:
Audio tapes are available in two types of format: open reel and cassette. They are available in various playing speeds and recording formats viz. monoaural, stereophonic, and quadraphonic and have tracking configurations like 2 track and 4 track.
Video tapes:
Video tapes are made of chromium dioxide or metal as the major constituent of the magnetic coating. In 1971, Sony Corporation introduced the first video recording U-matic system to use magnetic tape cassettes. The U-matic tapes measure 3/4 inch in width. In 1975, Sony introduced Betamax recorder using 1/2 inch video tape cassettes. This video cassette measure 6.1 inches wide by 3.8 inches high by 1 inch deep. In 1977, the Victor Company of Japan introduced VHS video cassettes. The cassette size is 7.4"x 4"x 1". The VHS video cassettes are identified by a code indicating recording time in minutes, when the recorder is operated at the normal play condition. The common length of VHS cassettes are T -120, having a two hour run time. Later on two other VHS version of video cassettes have been developed. They are: Super- VHS (S- VHS) and VHS-Compact (VHS-C). The image of S-VAS is of high quality and the cassette measure 4"x 2.5"x 0.5" in size. Now 8mm tape video cassettes are available in the market. A higher version of this Hi8 cassettes are used for digital recording. These cassettes measure 3.7"x 2.5"x 6" and the tape length varies from few minutes to more than one hour.
Discs
Magnetic discs are used with computers. They can be categorised as hard disk and floppy discs. Hard disks are stored within the computer service area.
Floppy disks:
The floppies used for recording digital data for computers are thin circular plastic sheets. These are usually covered with ferric oxide, like magnetic tapes. These discs are supplied in card or plastic covers, from which these should never be removed. Some discs are supplied in completely sealed containers. The density of information packed on to the recording surface is very high. Considerable effort is needed to protect it from any damage. As with magnetic tape, the degree of proximity between the head that records or reads the data coded magnetically, and the disc is extremely important. On this depends the accuracy of reading. It is, therefore, essential that dust and dirt do not gather at all on the head and the disc. It is also essential that the magnetic surface is not touched by hand and is kept covered as far as possible. Any greasy material picked up when touched by hand is disastrous. Floppy disks are still most widely used magnetic media, because of their easy portability and the facility for saving and deleting files as and when required. Nowadays only 3.5 inch diskettes having 1.44 megabyte of storage capacity are available. Other formats viz. 5.25 inch and 8 inch are now obsolete.
Hard disks:
Hard disks are high performance storage media having application in on-line and rapid access to data. A hard disk is made up of a stack of rotating metal disks on which data are stored. These are usually fixed inside the computer and hence are not physically accessible to the users. This implies that the care and maintenance of hard disks are performed by the hardware engineers and users are only required to know the operating procedures. Also, as the magnetic media rotate at a very high speed and data are read and recorded by a magnetic head. It is more vulnerable to damaged due to head crush or other hardware malfunctioning.
Stability of Recorded Information
Stability of recorded information in case of magnetic tapes has been reported to be between 10-20 years. Whereas, the life span of a video cassette is more than 20 years. As such, magnetic media are considered medium-term storage media having life span of 10 years. As discussed previously, stability here denotes the period of time during which a given medium permits reliable recording and retrieval of information. Reliability is determined by absence of permanent read/write errors in the recorded information. Error-free operation denotes one error per trillion recorded bytes (12.2 gigabytes). The magnetic media are vulnerable to accidental erasure by magnetic field, improper handling, inter-layer transfer, media wear and environmental effects.
Erasure:
In magnetic media, such as disks and tapes, recorded information can be erased by application of an opposing magnetic force of sufficient coercivity. Coercivity is defined as the field strength required to accomplish demagnetisation of the medium. It is measured in units called "Oersteds". The potentiality of accidental erasure is enormous as many office instruments and products are having magnetic properties. However, to completely erase information, the strength of a magnetic field must exceed the coercivity of the magnetic medium on which the information is recorded. The coercivity of a small bar magnet commonly encountered in homes and offices is 550-650 oersteds. Many commercially available magnets exceeds 700 oersteds coercivity and are so small that can be concealed in a pocket.
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