Quick Answers
A magnetic tape is a storage medium that consists of a magnetic coating on a thin plastic strip. It was commonly used to store data for computers from the 1950s to the 1990s. The data is stored by magnetizing spots on the tape surface. A tape drive reads and writes the data as the tape passes over magnetic read/write heads. Magnetic tape was known for its low cost and high storage density compared to other storage media.
What is Magnetic Tape Used For?
Magnetic tape was most commonly used for offline, archival, and backup storage. Some key uses of magnetic tape include:
- Backing up hard disk drives – tape was used to create backups of hard disk drives in case the disk failed or data was accidentally lost or deleted.
- Archiving data – organizations would archive old or unused data on magnetic tapes for long term storage and retrieval when needed.
- Exchanging data – the portability of magnetic tapes made them useful for transferring data between computers or locations.
- Sequential data access – applications with sequential data like census records or financial transactions stored data on tape.
In the 1990s, tape capacities reached hundreds of gigabytes to terabytes, making them useful for network servers, archives, backups and data interchange. However, disks became cheaper, faster and offered random access. By 2000, disks had surpassed tapes in most applications.
Brief History of Magnetic Tape
The key events in the history of magnetic tape data storage include:
- 1932 – German engineer Fritz Pfleumer patents the idea of coating a thin plastic tape with magnetic iron oxide powder.
- 1935 – AEG in Germany and BASF developed the first practical magnetic recording tapes based on Pfleumer’s patent.
- 1951 – UNIVAC I computer uses magnetic tape for data storage and input.
- 1952 – IBM introduces vacuum column tape drives for the IBM 701 computer.
- 1958 – IBM launches the IBM 729 tape drive which became an industry standard.
- 1962 – IBM introduces the 2400 series tape drives using the new 7-track format.
- 1964 – IBM System/360 launches supporting the new 9-track tape format.
- 1979 – Rotating-head helical scan tape drives are introduced allowing higher data rates.
- 1989 – Digital Linear Tape (DLT) launched offering higher capacity backup storage.
- 1996 – LTO tape drive technology is introduced providing up to 1.5 TB native capacity.
Magnetic tape faced competition from disk storage from the 1960s onwards. But its low cost kept it viable for backup, archival and sequential access applications until the 2000s, when disks fully overtook tape capacities.
How Does Magnetic Tape Work?
Magnetic tape stores data by magnetizing tiny iron oxide particles embedded on the tape surface. A tape drive pulls the tape across read/write heads to access the data.
The key components of magnetic tape technology include:
- Tape material – Polyester tape with a thin magnetic coating, typically iron oxide or chromium dioxide particles.
- Tracks – Long thin strips running the length of the tape where data is recorded.
- Write head – An electromagnet in the tape drive that magnetizes particles on the tape surface to write data.
- Read head – A sensor that detects changing magnetic fields on the tape to read back the data.
- Drive mechanism – Transports the tape across the heads at a controlled speed.
As the tape moves over the write head, the magnetic field aligns the particles into patterns representing the binary data. The aligned particles remain in place after the tape passes. Later, the read head senses the patterns of magnetic particles as changing magnetic fields, converting them back into the original data.
Linear vs. Helical Scan Recording
Tape drives use either linear or helical scan recording. Linear drives record tracks directly across the tape from edge to edge. Helical scan drives use rotating heads that write diagonal tracks across the tape at an angle. Helical scan recording enabled much higher data densities than linear recording.
Tape Formats and Generations
Key tape formats and generations include:
1. 7-Track Tape
- Used 7 parallel tracks for data recording.
- Introduced in 1952 for the IBM 701 computer.
- Tape width was 1 inch.
- Stored up to 2.3 MB on a reel of 2400 feet.
2. 9-Track Tape
- Increased to 9 parallel tracks.
- Launched in 1964 for the IBM System/360.
- Allowed 8 bits plus 1 parity bit per track.
- Stored up to 10 MB on a tape reel.
3. Cartridge Tape
- Introduced tape encased in a plastic cartridge for ease of use.
- Used 1/4 inch wide tape.
- Capacities up to 45 MB with linear recording densities.
4. Cassette Tape
- Used tiny cassettes instead of large reels.
- 1/8 inch tape width.
- Up to 1.6 GB capacity with helical scan recording.
5. DLT and LTO Tape
- DLT launched in 1989 offering higher capacity backup tape.
- LTO introduced in 1996 for automation and media longevity.
- Compressed capacities reached hundreds of GBs to TBs.
Magnetic tape steadily improved over 5 decades, increasing track counts, densities and drive mechanics to boost capacity, speed and reliability.
Advantages of Magnetic Tape
Magnetic tape provided the following key advantages as a storage technology:
- High capacity – tape could store large amounts of data, reaching multi-terabyte capacities in the 1990s.
- Low cost – the price per MB was very low compared to other storage media.
- Long term storage – tapes allowed data to be archived for decades.
- Portability – tapes were small and durable so data could be moved between locations.
- Fast sequential access – tape drives could read/write data very quickly as the tape streamed by.
- Reliability – tape offered error checking and correction features for data integrity.
These strengths made tape ideal for backup, archival and sequential access applications for decades.
Disadvantages of Magnetic Tape
Magnetic tape also came with the following limitations:
- Sequential access – data had to be read/written sequentially from start to end, not randomly.
- Slow seek times – seeking to different positions on tape took time to wind/rewind.
- Vulnerable media – the tape media itself could be damaged, stretched etc if mishandled.
- Large storage space – physical tapes libraries took up considerable storage room.
- Manual operation – accessing and mounting individual tapes was a manual process.
These factors ultimately led to magnetic disks replacing tapes for applications requiring faster random access and automated operation.
Major Tape Drive Manufacturers
Some leading magnetic tape drive manufacturers included:
- IBM – The early leader in tape drives starting in the 1950s.
- DEC – Digital Equipment Corporation made popular small format tape drives.
- HP – Major vendor of DDS and LTO tape drive products.
- Quantum – Leading vendor of DLT backup tape drives starting in 1989.
- Sun Microsystems – Created their own QIC and DLTcompatible tape drives.
- Imation – Major maker of data tape media and cartridges.
- Sony – Produced their proprietary AIT tape drive systems.
These companies drove much of the innovation in magnetic tape storage capacities, speeds and reliability over the decades before disks became dominant.
Types of Tape Drives
Major types of tape drives included:
1. Open Reel Tape Drives
- IBM 729 – early vacuum column reel-to-reel drive.
- IBM 2400 – used the new 7-track tape format.
- IBM 3420 – introduced automatic tape loading in the System/360.
2. Cassette and Cartridge Drives
- DEC TK50 – popular mini cartridge tape drive.
- HP 9895 – used double sided 3M DC300 cartridges.
- Wangtek – QIC cartridge tape drives.
- Iomega ZIP drive – patented single reel cartridge design.
3. Helical Scan Drives
- Exabyte EXB-8200 – first commercial helical scan tape drive.
- Sony AIT – Advanced Intelligent Tape helical drive.
- DLT – Digital Linear Tape with helical scan read/write heads.
Different vendors pushed various form factors optimized for capacity, speed, cost and reliability.
Magnetic Tape vs. Magnetic Disk
Magnetic tape and magnetic disk drives took different technology approaches to storing data. Some key differences include:
Magnetic Tape
- Data is stored on a thin plastic tape coated with magnetic material.
- Tape is pulled past read/write heads to access data.
- Primarily used for sequential data access.
- Very high capacities for archival data.
- Much slower random access compared to disk.
Magnetic Disk
- Data is stored on spinning rigid platters coated with magnetic material.
- Read/write heads move on an arm to access data.
- Supports fast, random data access.
- Used for primary storage and applications requiring random access.
- Generally less capacity than tape.
While tapes were cheaper per megabyte, disks provided faster access times and were better suited for systems and applications. The sequential nature of tape made it preferable for large backups and archives.
Demise of Magnetic Tape
Magnetic tape remained a viable storage medium for over 5 decades before being superseded by other technologies. Some key reasons for its demise include:
- Capacity lagged behind disk from the 1990s onwards.
- Newer optical and solid-state drives offered random access capability.
- Automated storage libraries and virtual tape reduced physical tape handling.
- Bandwidth constraints limited performance compared to disk and flash memory.
- New non-volatile storage technologies emerged for archival storage.
While tape is still used for some backups and archives, it has disappeared from most applications. Magnetic disk drives have taken over as the primary computer storage technology.
Conclusion
Magnetic tape played a pivotal role in early computer systems, offering an affordable medium for data storage and backup. For over 50 years, tape capacities and densities improved while costs declined. This made tape ideal for archival, backup and sequential data access applications.
However, the fundamental limits of tape technology made way for disks as the primary storage medium starting in the 1990s. While tape still has some backup and archival use, magnetic disks now dominate computer storage. But the long history of tape drives was foundational in enabling modern data-intensive computing.
