Digital Data Storage (DDS) (1989 – 2007)

Digital Data Storage (DDS) was introduced in 1989, and used a version of Digital Audio Tape (DAT) for storing data.

DDS used helical scanning on magnetic tape, and stored between 1.3 GB in the first generation (DDS-1) and 36 GB uncompressed on the fifth generation (DAT 72) launched in 2003.

During its life, DDS competed against formats such as Linear Tape-Open (LTO), Advanced Intelligent Tape (AIT), VXA, and Travan, and over 18 million DDS drives were sold.

Generally, DDS drives can read and write to media of one or perhaps two previous generations only, so DDS-4 drives cannot read or write from DDS-1 tapes. DDS drives cannot read or write to media from later generations.

Two later generations (DDS-160 and DDS-320) both use 8mm wide tape in a slightly thicker cartridge, whereas the first five generation of DDS used 3.81 mm tape (often labelled as 4mm DDS).

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Preservation / Migration

media stability 3obsolescence 3Whilst DDS drives are still available secondhand, a single drive cannot read more than three generations of DDS.

The earliest tapes are now nearly 30 years old


Metal tape Microcassette (1981 – mid-1980s)

The Microcassette was introduced in 1969 by Olympus for dictation purposes, but in 1981 and 1982 several devices were introduced that used the Microcassette for music recording and playback.

Several personal stereo devices, similar to the Sony Walkman were introduced, such as the Olympus SR-11, and there were also several Microcassette decks for Hi-Fi separates systems from brands such as JVC, Sanyo, Technics and Sony.

The Microcassette for music was a little different to the standard Microcassette and used metal tape (coated with pure metal particles rather than oxide) which had been introduced for the Compact Cassette in 1979 as this offered higher sound quality. Many of the new Microcassette music devices offered Dolby noise reduction, and of course this version of the Microcassette offered stereo sound.

A few pre-recorded tapes were released (mostly in Japan), but the format failed to take off and seems to have disappeared fairly quickly. Even at the time the tapes had limited availability and were expensive, and it’s now hard to find original metal tape Microcassettes.

Despite being used for music playback in its metal-tape form, the cassette seen in the 1971 film ‘A Clockwork Orange’ was the similar Mini-Cassette format and not a Microcassette.

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Microcassette (1969 – )

Introduced by Olympus in 1969 for voice recording, the microcassette uses the same width of magnetic tape as the Compact Cassette (3.81mm) but in a much smaller shell. By using thinner tape and half or a quarter of the tape speed, microcassettes can offer comparable recording time to the Compact Cassette. The original standard microcassette, the MC60, gives 30 minutes recording per side at its standard speed of 2.4 cm/s, and twice the time at 1.2 cm/s.

Because of the format’s relatively low fidelity, microcassettes have mostly been used for recording voice, for example in dictation machines and telephone answering machines. However, it has also been used as a medium for computer data storage and music. In the early  1980s, some Walkman-type devices, and even some home audio players for stereo recording and playback were produced, and metal tape (equivalent to Type IV metal tape in Compact Cassettes) was available for higher fidelity.

Microcassette was more suited to data and music recording than the Mini-Cassette as the tape is pulled through by the capstan and has a more constant speed, whereas in the Mini-Cassette, the tape is pulled by the reels.

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Preservation / Migration

Digital Compact Cassette (DCC) (1992 – 1996)

Digital Compact Cassette (DCC) was a digital audio recording format using magnetic tape, introduced by Philips and Matsushita in 1992. Pitched as a successor to Philips’ own Compact Cassette and competitor to Sony’s MiniDisc, it never became popular.

It shared the same form factor as compact cassettes, and DCC recorders could play back either type of cassette. This backward compatibility allowed users to adopt digital recording without rendering their existing tape collections obsolete.

As well as home players, portable and in-car players were produced.

Digital Compact Cassette was discontinued in October 1996 after Philips admitted it had achieved poor sales.

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Compact Cassette Type IV (Metal) (1979 – late 1990s)

The Type IV or metal-formulated Compact Cassette was introduced in 1979 by 3M under the trade name Metafine, and addressed a number of problems with previous tape formulations.

Standard Compact Cassettes (Type I or ferric-oxide) typically had poor high frequency definition, with pervasive tape noise (hiss). Type II (chromium dioxide) had much better frequency reproduction and very low noise but at the expense of some output level and low frequency solidity. Type III (ferro-chrome) was an attempt to restore some low frequency firmness but whilst Type III worked as a concept, it was not enough of an improvement to be taken up by the market.

Type IV was a completely new formulation using pure metal particles instead of metal oxides. This created a hard-wearing tape with superior frequency response and greater dynamic range.

It also had some disadvantages such as excess wear on tape heads, and they were expensive to buy. By the mid-1980s, metal tape did begin to catch on and was adopted by a lot of enthusiasts.

For tape recording equipment that was capable of using metal tape, there were extra indentations in the top of the cassette to identify it as Type IV and select the correct bias and equalization. On equipment without metal tape settings, it was possible to playback cassettes, but recordings would not be successful.

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Compact Cassette Type II (Chrome / High-Bias) (1970 – 2000s)

The Type II or chromium dioxide Compact Cassette was introduced to the market in 1970 by BASF.

Chromium dioxide provided an increase in high frequency response over the often rather muffled tone of the existing Type I ferric cassette, but took a while to take off as mainstream audio equipment available in the 1970s couldn’t make full use of the improvement in sound quality and it was only in the 1980s that chrome tapes become mass market.

Recording onto blank chromium dioxide tape ideally required the use of high-bias, and an EQ setting of 70μS. Pre-recorded music cassettes were often made to be played at 120μS (the same as ferric tape) to ensure wider compatibility.

An alternative formulation based around a cobolt / iron oxide was introduced in the mid-1970s and by the 1990s even BASF moved onto this substitute for chrome, although it was still labelled as chrome and was still high-bias.

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Streamer cassette (late 1980s – late 1990s)

Streamer cassettes were a variant of the Compact Cassette, specially designed for data storage (but different from standard cassettes used for data storage with early home computers) and had  a typical tape speed of 90 inches per second. Cassette tape streamers could be used with personal computers to make hard disk back ups.

They look almost identical to a normal Compact Cassette with the exception of a notch about ¼-inch wide and deep situated on the top edge of the cassette. Streamer cassettes also have a re-usable write-protect tab on only one side of the top edge of the cassette, with the other side of the top edge having either only an open rectangular hole, or no hole at all.

The whole of the ⅛-inch tape width is used for data, so there is only one ‘side’, but data is stored in four tracks in serpentine fashion.

Streamer cassettes could hold anywhere from 50 to 160 MB of data.

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Compact Cassette for data (1975 – late 1980s)

Early microcomputers often used punched tape for data storage, until in 1975 Jerry Ogdin and Les Solomon co-authored an article in Popular Electronics magazine about using inexpensive Compact Cassettes with audio tones to represent the binary data.

Many home computers of the late 1970s and early 1980s subsequently used cassettes for data storage as a cheaper alternative to paper tape or the floppy disks increasingly used in high-end microcomputers.

Typical speeds of loading were from 500 to 2000 bits per second, although some games used special, faster-loading routines, up to around 4000 bit/s. A rate of 2000 bit/s equates to a capacity of around 660 KB per side of a 90-minute tape.

Any type of Compact Cassette could be used, but smaller length cassettes such as C10 and C15 were produced for recording data.

Floppy disk storage become more prevelant by the mid-1980s, but cassettes remained popular for 8-bit computers such as the Commodore 64 and ZX Spectrum, particularly in the UK. Reliability of cassettes were variable, and multiple attempts to load programmes were sometimes required.

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DECTape II (1978 – early 1980s)

DECtape II was introduced around 1978 by Digital Equipment Corporation (DEC) for use in the TU58 tape drive, and was a specially formatted version of DC100.

DECtape II used 3.8 mm tape in a cassette format.

Like its predecessor, DECtape, a DECtape II cartridge had a capacity of about 256 kb. DECtape II cartridges could not be formatted by the end-user, and had to be purchased in a pre-formatted state.

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Endless loop Compact Cassette (1969 – 1990s)

Endless loop compact cassetteEndless loop cassettes are a variation of Compact Cassettes that play a continuous loop of tape without stopping.

They can range in length from 30 seconds upwards, and some include a sensing foil on the tape to allow tape players to re-cue. Uses include answering machines or musical jingles.

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