Magnetic tape is a long strip of thin plastic film coated with magnetic material called ferromagnetic oxide that can be magnetized to store audio, video, and data. The tape itself is not magnetic, but the magnetic properties of the ferromagnetic oxide coating allows it to record and play back information.
Magnetic tape recording was developed in Germany in the late 1920s and early 1930s. The earliest magnetic tape recorder was called the magnetophon and was developed by Fritz Pfleumer, based on earlier work by Danish inventor Valdemar Poulsen. The magnetophon used reels of magnetic tape made from paper coated with iron oxide powder. It allowed for the first time the recording and playback of high-fidelity sound. Commercialization began in the 1940s, most notably by AEG with its Magnetophon brand recorders. Magnetic tape brought about a major advancement in audio fidelity, quality and convenience over previous recording methods like vinyl records and wire recording. The technology was adopted worldwide during the 1950s and 1960s for audio recording.
Sources:
https://en.wikipedia.org/wiki/Tape_recorder
https://historictech.com/magnetofon-the-birth-of-magnetic-tape/
How Magnetic Tape Works
Magnetic tape consists of a plastic tape coated with iron oxide particles that can be magnetized to store audio or video data. The tape runs past a recording head that converts electrical signals from a microphone or other source into a magnetic pattern on the tape.
The magnetic particles are oriented in one direction or the other to represent binary data. A magnetized section on the tape is a 1, while a non-magnetized section is a 0. As the tape moves past the head, different magnetic patterns are created sequentially along the length of the tape to capture the audio or video signal over time.
During playback, the tape runs past a read head that detects the magnetic patterns and converts them back into electrical signals. An amplifier boosts these signals so they can be output to speakers or a video device. This sequential storage and readout process is what defines magnetic tape as a sequential access medium.
Some key inventions that enabled magnetic tape recording include biasing the tape to reduce noise (Fritz Pfleumer), adding an erase head to allow re-recording (Alexander Poniatoff), and developing the ring head design to fully contact the tape (John Mullin). These paved the way for magnetic tape to become a widespread consumer technology.
Sequential Access
Sequential access means that data is read from or written to storage media in a serial order, one record after the other (Collins Dictionary, 2022). This is in contrast to random access where individual pieces of data can be accessed directly without having to process the preceding data.
Magnetic tape data storage is an example of a sequential access storage device, as data is stored linearly along the length of a tape. Tape drives can only read the data in the order it is stored on the tape, from beginning to end (PCMag, n.d.). Data cannot be accessed randomly from different positions on the tape. This differs from random access storage like hard disk drives, where non-sequential data access is possible.
Overall, with sequential access on magnetic tape, data must be accessed sequentially from start to finish. Individual records cannot be directly reached, only accessed by reading/writing the preceding data (The Free Dictionary, n.d.). This serial reading of data is inherent to the linear format of magnetic tape.
Advantages of Sequential Access
One of the main advantages of sequential access on magnetic tape is that it allows for faster read speeds compared to random access. As the tape runs continuously past the read/write head, data can be read in a single, sequential pass without having to stop and reposition the tape frequently (Compscistation, 2018). This streamlined process results in data transfer rates of up to 1 GB per second for modern magnetic tape drives.
Sequential access also allows for a simpler mechanical drive design. Since the tape drive does not have to rapidly start, stop, and reposition the tape multiple times to locate and access different data blocks, the engineering and motion control systems can be less complex compared to drives that support random access. The tape simply needs to maintain a constant linear velocity as it moves past the head (Sciencedirect, n.d.). This simplicity enables high storage capacities and cost savings.
Disadvantages of Sequential Access
One of the main disadvantages of magnetic tape is the sequential access. Data is stored linearly along the length of the tape. To reach a specific piece of data, the tape drive must physically wind and unwind the tape until it reaches the desired location (Salvagedata). This makes random access of data very difficult. Unlike hard disks or solid state drives, magnetic tape cannot quickly jump to a random location to read or write data.
With sequential access, if the data being sought is at the end of the tape, the entire length of tape must pass by the read/write heads before reaching it. This makes accessing individual files or data blocks extremely time consuming compared to random access storage. The linear operation requires starting at the beginning and reading all the data sequentially until reaching the desired section (Compscistation). This aspect makes tapes ill-suited for applications requiring fast random data access.
Attempts at Random Access
While magnetic tape is designed for sequential access, there have been attempts to enable some level of random access over the years. In the 1960s, IBM developed the IBM 1360 Photo-digital Storage System which used photographic film as the medium and could rapidly search for data by moving a light source to the desired location. However, it had limited storage capacity and was expensive.
In the 1970s, Exabyte Corporation developed a technique called interleaving to allow faster access to data on tape. This involved rearranging blocks of data so related content could be accessed more quickly. While not true random access, it improved access times. DEC also released the DECtape II system which supported limited random access capabilities.
Modern Magnetic Tape Uses
Today, magnetic tape is still commonly used for backup and archival storage, especially by large data centers, servers, and corporations. According to Wikipedia, magnetic tape is well-suited for backup because of its “longevity, low cost, high density and energy efficiency” [1]. Backup tapes allow large amounts of data to be stored offline for years at a relatively low cost. The tapes can be transported to off-site facilities for protection against disaster or cyberattack. Major cloud providers like Amazon and Google use magnetic tapes to back up their data centers [2].
In addition to backup, archival storage is a key modern use case for magnetic tape. Tape has a longer shelf life than hard drives and does not require power to maintain stored data. The high data density of modern tape cartridges, up to 185 TB per cartridge, makes it very efficient for storing large archival datasets [1]. Government agencies, research institutions, and other organizations with large archival requirements still rely on magnetic tape for cost-effective long-term storage.
Decline of Tape for Consumers
While magnetic tape was once very popular for data storage and backup among consumers, its use has declined significantly with the rise of random access storage mediums like hard disk drives and solid state drives. Hard disk drives, first introduced in the 1950s, allow for non-sequential access to data. This means the drive’s read-write head can jump instantly to any location on the disk to access data, rather than having to read all the preceding data sequentially as with tape. Solid state drives, which store data in flash memory chips and have no moving parts, brought further advantages like faster access speeds, durability, small size, and low power usage. These random access technologies made data retrieval much faster compared to sequential tape, which had to scan through the entire tape to find a file. As disk and flash storage improved while also dropping in price, magnetic tape became impractical for everyday consumer use. According to the Information Age, the arrival of disks led to a “significant decline in tape’s popularity” before solid state took over as the dominant storage medium. While tape is still used commercially for archiving and backups, hard drives and SSDs have replaced tape for most consumer applications.
Source: https://www.information-age.com/rise-fall-and-re-rise-magnetic-tape-30854/
Future of Magnetic Tape
Despite the decline in consumer usage, magnetic tape continues to have an important role in data backup and archival storage. According to Horizon Technology, tape is well-suited for these applications due to its “reliability, longevity, energy efficiency and low cost” (Get That On Tape: The Past and Future of Magnetic Tape Storage).
Tape cartridges can be stored offline and have a long shelf life, making them ideal for archival purposes. The high capacity of modern tape (up to 185 TB per cartridge) means a large amount of data can be stored in a small physical space. Tape is also more cost effective for long-term storage compared to hard disk drives.
Major technology companies like Google, Amazon, Microsoft and IBM continue to use tape as part of their data center backup and archiving strategies. According to industry analysts, the market for tape drives and media is expected to grow over the next several years as data storage needs increase exponentially.
While no longer used for primary storage, magnetic tape is still a crucial technology for any organization needing an air-gapped, offline data backup. Tape will likely continue serving this key role for the foreseeable future.
Conclusion
As we have discussed, magnetic tape uses sequential access for reading and writing data. This means that the tape must physically wind past the read/write heads in order to access different parts of the data. The linear method of access provides some advantages, such as simplicity of design and low cost. However, it also has drawbacks like slow random access.
Although random access on tape has been attempted through innovations like helical scan recording, tapes work most efficiently when data is stored in a sequential format. This has led magnetic tape to be used primarily for sequential data like backups, archives, and some streaming media. While tape has faded for consumer use, it continues to be a reliable choice for long-term data storage in enterprise and scientific settings.
In summary, the sequential access of magnetic tape has both enabled it to thrive in some applications and limited it in others. But tape’s longevity shows that sequential data access remains useful decades after magnetic tape’s introduction.