How is Data Stored on Tape?

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Introduction to tapes

Tape is a narrow strip being magnetized on one side of the strip. To store data, the narrow strip goes through below the magnetic head which stores the data into bits. Various data are stored on the strip. It helps in storing digital information. They are commonly used in cartridges and cassettes. This tape helps in recording audio or visual and data or software as well.

Data storage helps in performing the function of write to and read from on a magnetic tape.

Cassette is enclosed with two reels. The magnetic tape used has a single span of use whereas the cartridge is a device enclosed with a single tape.

In optical disc recording, a laser is used. The laser burns microscopic holes onto the dye layer. Then a weaker laser reads the signals.

To store data on digital cassettes, read or write head moves quickly. This quick movement of the reading/write head enables to maintain speed which would be enough to maintain the bits at a manageable size.

UNIVAC is the first computer to use tape for data storage.

Advantages of storing data on tape

Tape can be very beneficial if the user’s main purpose of buying a storage drive is to have a high capacity of storage. It is nothing new that tape storage gives high capacity storage. Compared to its competitors, the tape is also less expensive. It provides the benefits of backup storage and archival storage. As these devices are compact in the device they are easy to store. Along with all these, these tapes are secured with the requirement of authorization to access data which is an essential feature required by large-scaled companies to secure their data.

How does tape store data?

The tape is a narrow strip having a coating of iron oxide or a material that can be magnetized easily or magnetic oxide. Only one side of the tape has a coating. To record on tape, electrical signals are passed to make an imprint on tape. The tape goes through a recording head leading to an imprint on the tape. Then the tape passes through playback or reproducing head which produces a signal and then induces a recorded signal. This signal then increases the intensity to align with the output equipment.

When magnets magnetize these magnetic oxides, the magnetize oxides then retain the magnetization. The magnetization remains until the magnetization is forced to change. To change magnetization, the tape is required to go under another magnetic reading, i.e., the tape retains the magnetization.

It is well known that computers read or write data in with a series of binary numbers which are “1” and “0”, which is a machine language. Here, in magnetic tapes, the data is stored or magnetization occurs in tape with the use of the North Pole or the South Pole at either end, to explain, it is in either upward direction or downward direction. Now, to represent data like binary code, the directs are used instead. Tape first breaks down the data into bits which is why the tapes have blocks to store a bit size of memory. In these blocks, the data is represented either in the North Pole or the South Pole at either end.

As mentioned earlier, the tape goes below the electromagnetic head. The magnetic head is approximately aligned with the space assigned to store data into bits. The magnetic head then directs the magnetic field towards the space designated for bits which magnetizes the bits. When the magnetic head passes by while magnetizing the bit, the bit turns either up or down because of the directions of the magnetic field which is received by the magnetic head. The direction of bits depends on the direction of the magnetic field received by the magnetic head. This step revises the position of the bits. Then to read, the read head is used at the tip of the actuator arm.

In the case of disk tape, the motor of the arm rotates aligned with the motor of the actuator arm. If these two motors are not in alignment, then there may overlap of data and records may mix up. If they are not aligned, then there will error in data.

While magnetizing the tape, seven or nine bits are recorded. These bits are recorded parallel across the width of the tape. While to read or write, the read or write head reads or writes the bits in parallel. On magnetic tape, the data are organized which are then called records. These records are separated by gaps for synchronization to avoid overlapping of data or collision of data. These sets of records are then called files. To locate the beginning of the file, a file mark is used. To identify a file, a header or an identifier is used. The record following the file mark is represented as a header or identifier. This header identifies the file based on search commands by the user. Read and write heads are fixed.  The tape moves at linear velocity towards the read and writes head due to which, the later the data is written. Anytime the user wants to read a particular record, the read or write head will go through all the previous set of records to reach the particular record.

Nowadays, the capacity of tape is increasing but there is very little significant change in the model. Companies now use magnetic logic as an essential component to store data on tape which will enable the data to be stored more effectively. It is able to store more effectively as the logic system performs the action with speed and retains information even after being switched off. This file mark can be a single special character or a multiple-character record.

To record on magnetic tape storage, there are two methods generally followed which are:

Linear

In this method, data is arranged into parallel tracks. Parallel tracks help in spanning the length of the tape. To write on a medium track with parallel tape tracks, multiple tape heads are simultaneously used. It was used in older versions of tapes. It is a simple method of recording although it has the lowest data density.

Now, the linear serpentine version is used for linear technology recording. It helps in tracking multiple tape heads. Still, only one track is written at a time by a single head. Compared to an earlier version, the previous version used to store data on parallel sides simultaneously but in the new version, first data is written on one line and then data is written to its parallel line. The head slightly shifts and passes to a reverse direction writing another set of tracks. After this process has been started, it stops after all the tracks are written or read. In the new version of the linear recording method, the medium can have more tracks than reading/write heads whereas in the older there was the same size of tape length and the same quantity of heads. This feature of linear serpentine increases the capacity of data storage in the newer version, linear serpentine.

Scanning

In this method, recording is not done along the length of the tracks. This method writes short dense tracks across the width of the tape medium. While scanning, although the disk runs rapidly the tape moves slowly compared to the speed of the disk. The transverse scan was more preferred compared to the ongoing linear method as the scan provides a higher data rate. Under this process, to write or read data from the tape, a tape head with a spinning disk is kept towards the outer edge and placed perpendicular to the path of the tape. Before the transverse method, an arcuate scan was used. The arcuate scan method uses the read or writes head on top of the spinning disk which was kept flat. Since the spinning disk was laid flat against the tape, the tape head was used to form an arc. With the help of a helical scan, the recording is written in a diagonal manner. Helical scan records in short dense tracks. This method is currently followed by the current videotapes systems and several data tape formats.

Should you store data on tape?

Maintaining tape is a very concerning matter. Not only securing it from potential thefts as it is in a portable form but also maintaining the disk separately. Any disturbances while recording or any strong source of the magnetic field other than coming from magnetic will hamper the recording of data onto tape. Even after storing data on the tape, the tape is required to be out of reach of any strong magnetic field or sunlight. The environment is also supposed to maintain cleanliness as the magnetic tapes being magnetic in nature are prone to attract dust particles thus damaging the data. Compared to other forms of data storage units, if tapes are not handled properly, a hard hit or not handled properly will also lead to breakage. If tape storage is maintained properly then the tape storage will keep the data secure and available for nearly three decades compared to other forms of data storage and prove to be cost-efficient.