Magnetic tape is the tape that holds data. It is a medium for magnetic recording made of a thin magnetizable coating on a long, narrow strip of plastic film. Magnetic tape revolutionized broadcast and recording with its introduction in the mid-20th century.
History of Magnetic Tape
The earliest magnetic storage devices were invented in the late 19th century. Oberlin Smith and Valdemar Poulsen independently developed methods of magnetically recording sound. Poulsen’s Telegraphone used steel wire to record audio signals. Fritz Pfleumer later created a method of coating cigarette paper with iron oxide powder to make magnetic stripes. This allowed for the development of paper strips and then tapes as storage mediums.
In 1928, Fritz Pfleumer developed the first reel-to-reel tape recorder, called the Magnetophon. It used plastic tape coated with magnetic iron-oxide powder as the recording medium. In 1932, BASF began manufacturing acetate-based magnetic recording tape, which became the standard. Acetate has fairly high coercivity, meaning it can record high density digital data.
During World War II, both the Axis and Allies militaries used magnetic tape for audio recording. Broadcast use of tape sparked after the war. In 1947, Bing Crosby invested in Magnetic Tape Sound Recording technology developed by Jack Mullin. Crosby then used it to pre-record his radio programs.
The commercial development of audio tape helped fuel other applications like analog computer data storage and early digital recording. In 1951, UNIVAC I used metal strips of tape for data storage. IBM used vacuum columns and then tape in its IBM 726 tape drive introduced in 1952. By the 1960s, magnetic tape supplanted earlier forms of storage like wire recording and audio disks.
Advances in Magnetic Tape
There have been many advances in magnetic tape over the decades:
- In 1935, Germany began using AC biasing to dramatically improve sound quality.
- In 1947, 3M Company developed the first audio tape using paper laminated with Scotch brand cellulose acetate magnetic coating.
- In 1962, Phillips introduced the compact audio cassette tape.
- In 1964, IBM introduced the IBM 2400 series 9-track tape system using 1⁄2” wide tape.
- In 1979, Sony introduced the Walkman portable cassette player.
- In the late 1970s, metal particle (MP) tape was introduced for higher density data storage.
- In the 1990s, digital linear tape (DLT) was developed for computers.
- In the 2000s, modern digital tapes like LTO Ultrium emerged for backing up data centers.
Today, magnetic tape continues advancing in its storage density and durability.
How Magnetic Tape Works
Magnetic tape records data by magnetizing tiny magnetic particles embedded on its surface in patterns. It consists of a thin magnetizable layer bonded onto a flexible plastic film substrate.
Tape drives pull the tape across read/write heads to access data. The heads create a magnetic field to imprint data patterns onto the tape. They also detect the magnetized patterns to read back data later.
A tape drive threads the tape from a supply reel to a takeup reel via guides and rollers inside a protective housing. It rotates the reels to move tape across the heads. Tape drives also precisely control tape speed and tension.
Tape Composition
Polyester film is the most common substrate used to create magnetic tape. Other materials like PEN polymer may also be used as the base film.
The base film is coated with a magnetizable layer containing iron oxide or other magnetic particles suspended in a polymer binder. Other coatings may be added for durability and friction reduction.
Backcoating is applied to the non-recording side to minimize static, improve winding, and reduce wear. A series of servo bands are prewritten along the tape’s length to enable precise head positioning.
Recording Method
Linear tape recording stores data in long parallel tracks that run the length of the tape. The servo bands bracket the data bands to guide the heads. As tape passes over the head at a fixed speed, the head magnetizes small spots in patterns.
Serpentine recording writes parallel but angled diagonal tracks across the tape sort of like tilling a field. The heads then cross over to the next track. IBM’s serpentine R-DAT format achieved higher capacities.
Helical Scan Recording
Helical scan recording writes short diagonal stripes across the tape sort of like wrapping a pole with ribbon. The rotating heads trace a helical path to record stripes of data.
Helical scan heads mount on a rapidly spinning drum. The angle of the stripes allows many more tracks. Video cassette tapes use helical scan. However, linear methods offer higher data rates.
Magnetic Tape Formats
There are a variety of magnetic tape formats that differ in things like track layout, tape width, cartridge types, and recording methods used. Below are some common tape formats.
Open Reel Tape
The earliest tape formats were open reels of tape 1/4″ or wider wound on removable reels. Analog audio and video recorders once used large open reels. Computer tape drives also employed open reel tapes.
Cassette Tape
The compact cassette tape gained widespread consumer adoption after its 1963 launch for portable audio. Cassette tapes confine tape in a protective plastic housing to make them easier to handle.
Cartridge Tape
For data storage, cartridge tape encloses reels of tape in a rugged external housing for pluggable convenience. Single-reel cartridges like IBM 3480 reverse tape direction. Enclosed dual-reel formats span short distances between reels.
Digital Data Storage Tape
Modern digital data tape comes in cartridges storing much more data with higher densities and more tracks than earlier analog formats.
Common types like LTO Ultrium employ linear serpentine recording and have tape widths between 0.5″ and 1″. Capacities range from tens of terabytes to hundreds of terabytes per cartridge.
Magnetic Audio/Video Tape
Consumer magnetic tapes for audio or video recording come in cassette, cartridge, and open reel tape formats.
Audio cassettes and video cassettes use formats like VHS and Betamax. Digital formats like DAT and DCC were also developed but adoption waned with other technologies.
Advantages of Magnetic Tape
Magnetic tape continues to be a viable storage medium even in the digital age due to key advantages:
High Capacity
Tape cartridges can store tens or hundreds of terabytes of data. A single LTO-9 cartridge holds 18 TB raw capacity. Tape has far higher capacities than other portable media.
Reliability
If stored properly, tape formulations like barium ferrite can retain data for decades. Bit error rates are very low, on the order of 1 error per 10^19 bits. Tape is more reliable than hard disk drives.
Cost Effective
Tape has very low media cost per terabyte compared to disk or flash technology. The $/TB is fractions of a cent for LTO Ultrium. Tape also has a long life span if handled well.
High Performance
Enterprise tape drives now deliver data transfer rates up to 400 MB/sec for LTO-9. Performance scales with multi-drive libraries. Tape also enables fast sequential data access.
Portability
The compact cartridges make tape very portable and easy to handle. Robotic silos automate cartridge management and backup operations.
Long Term Archival
For archival data that needs to be retained and preserved for years, magnetic tape is very cost effective and reliable. The linear format simplifies access.
Disadvantages of Magnetic Tape
Tape has some disadvantages that can make it less ideal in certain use cases:
Access Speed
While streaming speed is fast, random access to locate and position to data takes time. Disk or flash storage offer faster random data access.
Durability
The plastic tape substrate can be damaged if mishandled or exposed to poor environmental conditions. Tapes need to be stored properly.
Capacity
While high, tape capacity is limited per cartridge. Data must be split across a tape library. Online disk arrays now offer more capacity.
Cost
The drives, robots, and media cost significantly more than hard drive storage or cloud storage subscriptions.
Impermanent Storage
Tape is best suited for backup, archival, and tertiary storage tiers. It should not be used as a primary storage system due to slower access.
Uses of Magnetic Tape Storage
Magnetic tape continues to be used for the following primary applications:
Backups
Tape is ideal for regular computer system backups because it is portable, removable, and more reliable and secure than hard disk or flash drives. Tapes can be rotated offsite.
Archival Storage
The low cost per terabyte and long-term reliability make tape well-suited for archiving infrequently accessed data that needs long-term preservation.
Big Data Storage
The high capacities of modern cartridge tapes make them useful for storing enormous datasets like scientific research data that only needs infrequent access.
Video Archives
Media organizations store huge video libraries on magnetic tapes. The linear nature simplifies access and editing operations.
The Future of Magnetic Tape
While tape has declined from its peak decades ago, it continues advancing in new ways:
Higher Capacities
Ongoing improvements in recording density continue driving cartridge capacities higher to keep tape cost effective compared to disk and cloud data storage.
New Materials
New magnetic particles like barium ferrite (BaFe) and advanced film substrates support higher density recording with greater reliability.
Shingled Magnetic Recording
SMR overlaps tracks like shingles to increase density. IBM demonstrated 345 TB on a single cartridge using SMR techniques.
New Applications
High-capacity low-cost tape storage may enable new big data applications not feasible with primary disk or flash storage.
Conclusion
Magnetic tape has evolved substantially over decades of development while retaining key advantages in capacity, longevity, and cost. Tape carves out a role in the data storage hierarchy complimentary to hard disk drives and solid state storage. While challengers have come and gone, tape media continues adapting and remaining relevant today as an ideal medium for affordable high-capacity storage.
