Magnetic tape has been used for data storage since the early 1950s, with the first commercial magnetic tape drive introduced by IBM in 1952. Tape drives record data on reels of magnetic tape in the form of magnetic patterns. The plastic tape is coated with a magnetic material that can be polarized to represent binary data. Tapes are inexpensive, portable, and have very high storage density thanks to the ability to tightly pack data tracks onto tape.
Key metrics for tape are storage capacity, which refers to the total amount of data that can be stored on a tape cartridge, and areal density, which measures how densely data can be packed and is measured in bits per square inch (bpsi). Early tape drives had capacities in the megabyte range, while modern tape cartridges can hold 10s of terabytes. This has been enabled by astonishing increases in areal density, from around 2,000 bpsi in the 1950s to over 224,000 bpsi in the latest LTO-8 format.
Recording Method
Magnetic tape is made of a thin plastic film substrate that is coated with a magnetizable layer consisting of microscopic iron oxide particles. When recording data, the tape is moved past electromagnetic write heads inside the tape drive which generate magnetic fields and orient the iron oxide particles into patterns corresponding to binary 1s and 0s (https://www.youtube.com/watch?v=3LjD9OQmvro). There are two main recording methods used for magnetic tape: longitudinal recording and perpendicular recording.
In longitudinal recording, the magnetic patterns representing the data run along the length of the tape and parallel to the direction of tape motion. The data is stored in tracks that run down the length of the tape. Each track is comprised of many flux reversals or transitions between magnetic polarities. The linear recording density refers to how closely these flux reversals can be packed. Early tape drives used 7-9 tracks with densities of 800 flux reversals per inch. Modern tape drives use hundreds of tracks with densities above 300,000 flux reversals per inch (https://circulatingnow.nlm.nih.gov/2016/02/25/medlars-i-grace-the-early-mainframe-experience/nlm_medlars_17-cropped/).
In perpendicular recording, the magnetic patterns are arranged perpendicular to the direction of tape motion. This allows for greater storage densities since the magnetic poles are closer together. Bits can also be arranged in two dimensions across the width of the tape rather than just linearly along a single track. Most modern tape drives use perpendicular recording to maximize capacity.
Areal Density
Areal density refers to the amount of data that can be stored in a given surface area of a magnetic storage medium, usually expressed in gigabits per square inch (Gb/in2) (Wikipedia, 2021). It is a key factor determining the storage capacity of magnetic tape.
Over the decades, advances in magnetic tape technology have steadily increased areal density. In the early days of magnetic tape in the 1950s, densities were less than 1 Gb/in2. IBM’s 3480 cartridge tape system, introduced in 1984, achieved a density of 30 Gb/in2. In 2010, IBM and Fujifilm’s prototype tape achieved a density of 29.5 Gb/in2, allowing for the storage of up to 35 TB of uncompressed data on a single LTO-sized cartridge (Sciencedirect, n.d.).
Current state-of-the-art products like the IBM 3592 Jaguar can achieve areal densities of up to 123 Gb/in2. In their roadmap, Fujifilm and IBM aim to reach 317 Gb/in2 in current perpendicular magnetic recording tape, and up to 148 Gb/in2 for enterprise tape and 185 Tb/in2 for exploration tape in their advanced concept called NANOCUBIC technology (IBM, 2015).
Tape Formats
Magnetic tape comes in various physical formats like open reel tapes, cassettes, and cartridges. Common data tape formats include:
- Linear Tape-Open (LTO): An open standards magnetic tape format developed by technology companies like IBM, HP, and Quantum. LTO-8 is the latest generation, providing 12 TB native capacity and 30 TB compressed capacity. LTO offers high capacity and reliability, but drives and media can be expensive.
- Oracle T10000 T2: Oracle’s proprietary high-capacity data tape format with native capacity up to 12.5 TB and compressed capacity up to 37.5 TB. Provides ultra-high capacities but uses a proprietary format.
- IBM 3592: IBM’s high-end proprietary magnetic tape system aimed at mainframe and enterprise use. The latest TS1150 model offers up to 15 TB native capacity. Reliable but uses proprietary and more expensive technology.
- Sony Optical Disc Archive: Uses optical discs in cartridges like magnetic tape. Currently offers up to 3.3 TB capacity. Offers very long archival durability but lower capacity than magnetic tape.
Tape formats like LTO and Oracle T10000 offer higher overall capacity thanks to data compression, while formats like 3592 and ODA focus on high native capacity. Proprietary formats provide reliability and performance but can carry a higher cost. Open standards like LTO allow interchangeability between vendors.
Drive Technology
Magnetic tape drives rely on several key components to read and write data onto tape media. The main components include the tape head assembly, read/write heads, motors, controllers, and servo positioning mechanics (Source). Tape drives use either linear or serpentine recording methods. In linear recording, the tape passes by a stationary head in a straight line. Serpentine recording involves the head moving back and forth diagonally across the tape as it passes by (Source). Serpentine recording enables much higher data densities. The read/write head technology has evolved from early ferrite and metal-in-gap heads to thin-film heads and later to advanced thin-film and magnetoresistive heads, enabling substantial increases in areal density (Source).
Error Checking
Magnetic tape uses error checking and correction to detect and fix errors that can occur during reading and writing. Some common methods include even/odd parity checking, ECC (error correcting codes), and CRC (cyclic redundancy checks).
Parity checking involves adding an extra parity bit to each block of data that indicates whether the number of 1s in the block is even or odd. By checking the parity bits, errors can be detected. However, parity alone cannot correct errors. More advanced ECC uses complex algorithms to both detect and correct multiple errors in a block by adding redundancy.
CRC calculates a checksum value for each block that gets checked on reading to validate the data has no errors. If the checksum doesn’t match, the block is flagged as corrupted. CRC can detect but not correct errors.
These error checking mechanisms allow magnetic tape to reliably store data by correcting minor errors and detecting unrecoverable errors. However, they also reduce storage capacity since extra parity/ECC/CRC bits must be added. More advanced error correction allows tapes to pack data more densely while maintaining reliability.
Current Records
Magnetic tape continues to reach new heights in storage capacity as areal density increases. In 2017, Fujifilm demonstrated a record 223 terabits per square inch on linear tape open (LTO) technology, storing 330 terabytes on a single cartridge.[1] Sony also achieved 201 Gb/in2 areal density on tape in laboratory demonstrations.[2]
In terms of commercial products, the highest areal density available today is LTO-9 with 18 TB native capacity (36 TB compressed) per cartridge.[3] LTO roadmaps foresee capacities up to 192 TB native per cartridge by the mid-2030s.[4] Other leading formats like Oracle’s T10000 T2 tape hold up to 8.5 TB natively.[5]
While hard drives currently offer higher capacities for stationary data, tape retains key advantages for long-term archival storage including cheaper overall storage costs, energy efficiency, and reliability over decades.
Advantages
Magnetic tape has several key advantages compared to hard disk drives (HDDs) and solid state drives (SSDs) for long-term data archiving applications. Some of the main benefits include:
Durability – Magnetic tape is far more durable than HDDs or SSDs for long-term storage. Tape can withstand dust, magnetic fields, humidity and temperature fluctuations much better than other media. Tape cartridges stored properly can retain data for 30 years or more.1
Energy efficiency – Tape drives consume very little energy when not actively reading/writing data. This results in lower energy and cooling costs compared to always-on spinning hard drives.
Portability – Tape cartridges are small and lightweight, making them easy to physically transport and store offsite for disaster recovery.
Cost – Although the initial tape drive investment is high, the low media costs and high capacities make tape very affordable for large archives. Tape has a much lower total cost of ownership compared to HDDs or SSDs at petabyte scale.
Reliability – Modern tape drives have very low failure rates when used properly. The linear method of accessing data makes tape less prone to damage than mechanically spinning hard drives.
For these reasons, magnetic tape remains highly advantageous for long-term data archiving, backup and cold storage applications despite the emergence of newer technologies.
Disadvantages
Despite the high storage capacity and data archiving abilities of magnetic tape, there are some key drawbacks to consider (Source):
Magnetic tape has very high latency, which means there is a delay in the time it takes to locate and retrieve data from the tape. This makes accessing specific data very slow compared to hard disk drives or solid state storage. The average latency can be 30-60 seconds. Throughput or data transfer speed is also quite slow for magnetic tape (Source).
The equipment required for magnetic tape storage like tape libraries and drives can be quite expensive. The media tapes themselves can also be costly compared to hard disk drives. This results in high startup costs to implement a magnetic tape system.
In summary, the two main disadvantages are the slow access times and high costs associated with magnetic tape storage.
Future Outlook
The future looks bright for continued innovation and advancement in magnetic tape storage technologies. Several emerging technologies promise to push areal densities and tape capacities to new heights.
Shingled magnetic recording (SMR) is one promising approach that overlaps data tracks like shingles on a roof to increase areal density. Barium ferrite magnetic particles can also enable higher density recording due to their lower noise properties compared to traditional iron oxide particles. Laser assisted magnetic recording uses heat from a laser to temporarily raise a small region to its curie point, allowing very localized magnetic orientation at high densities.
With these new innovations, analysts predict areal densities may reach a milestone of 100 Gb/in2 in the next few years, leading to tape cartridge capacities in the hundreds of terabytes. As storage needs continue growing exponentially, particularly with big data, tape’s low cost and high capacities will solidify its role for long-term archiving, backup and cold storage applications.
Tape will remain a crucial part of the storage hierarchy and infrastructure, complementing faster disk and memory technologies. While its sequential access means tape does not serve all use cases, tape’s longevity, energy efficiency and portability make it an indispensable medium for cost-effectively storing massive amounts of infrequently accessed data.