5.25-inch ‘flippy’ disk (1976 – mid 1980s)

Flippy disk was a nickname given to single-sided floppy disks that had a second write-enabled notch cut into the sleeve so that the second side could be written to by a single-sided disk drive. Generally, these were 5.25-inch minifloppy disks, but 8-inch floppy disks could be modified in the same way, and this was possible because most of the openings on the sleeve of the disk were duplicated on both sides. It was a way of doubling the capacity of a floppy disk at a time when disks were expensive, although of course they had to be removed from the drive and turned over to access the extra capacity.

When the 5.25-inch minifloppy disk was introduced in 1976, all drives were single-sided. Double-sided drives were introduced in 1978, but suffered from early reliability problems. It wasn’t until 1982 that double-sided drives were supported by IBM PC-DOS in version 1.1. Drives such as Apple’s Disk II and the Commodore 1541 remained single-sided.

The second write-enabled notch could be made by hand, or special ‘disk doubler’ rectangular hold puncher could be bought to do the job. Flippy disks were also sold ready-made, and software was distributed on flippy disks that might have different programs on each side, or the same program but for different operating systems. Flippy disks sold for use in double-sided drives needed to have two index holes on either side of the hub hole.

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Ultra Density Optical (UDO) (2003 – )

Ultra Density Optical (UDO) is an optical disc data storage format that uses phase-change, and blue laser technology (similar to Blu-ray) to store substantial amounts of data on a disc in a cartridge very similar to the older 5.25-inch magneto-optical disc format that it was developed to replace.

UDO discs were first announced by Sony in 2000, and launched by Sony and Plasmon in 2003 with a capacity of 30 GB. UDO 2 was launched in 2007 with a capacity of 60 GB.

UDO discs are available in rewritable format, or as write once in which case the phase change method used means the data cannot altered once written (True WORM) making it very stable for long-term storage. A third format became available in 2005, Compliant WORM, that allows specific data on the disc to be destroyed while leaving other files intact.

As of 2017, UDO drives and discs are still available but since 2008 all brands of UDO disc have been manufactured by Mitsubishi in Japan.

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SyQuest 5.25-inch (44/88/200MB) (1988 – 1998)

The SyQuest 5.25-inch disks were removable hard-disk cartridges, initially introduced by SyQuest in 1988.

The SQ400 cartridge had a capacity of 44 MB, and the SQ800 (released in 1991) had a capacity of 88 MB. Initially, the 88 MB drives could only read and not write to 44 MB disks until a combination drive was introduced. The SQ2000 disk was introduced in 1994 and had a capacity of 200 MB.

The 5.25-inch generation of SyQuest disks were popular with Apple Macintosh owners, and used to transfer and backup large amounts of data by graphic artists, musicians and engineers.

By 1993, SyQuest had begun releasing smaller 3.5-inch form factor disks. These were popular, but because of the huge installed base of the SyQuest 5.25-inch drives, the 3.5-inch cartridges were not as successful as them.

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Bernoulli disk 5.25-inch (1987 – 1994)

Iomega released the Bernoulli Box II in 1987, replacing the original Bernoulli Box with its 8-inch disks with a smaller version using 5.25-inch form factor disks. Initially offering the same capacity of 20 MB as the original, this was increased over time, and eventually offered 230 MB by the time it was replaced by the Zip disk.

Unlike the original Bernoulli Box, the Bernoulli Box II was available as an internal unit, although it was still available as an external unit with one or two drives in a self-contained case connected via an external SCSI interface.

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5.25-inch minifloppy disk (1976 – early 1990s)

The 5.25-inch floppy disk (or ‘minifloppy’) was a magnetic disk format introduced by Shugart Associates in 1976, as a replacement for the 8-inch floppy disk that was considered too large for newer desktop machines.

Like the 8-inch floppy, the 5.25-inch disk consisted of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removed dust particles. Write protection was carried out by affixing an adhesive tab.

By 1978 a number of manufacturers were producing disks, in competing formats including hard and soft-sector versions, and different encoding schemes.

Initially, 5.25-inch disks had a capacity of 110 KB, with a double-density disk introduced in 1978 with a capacity of 360 KB, and quad-density introduced in the early 1980s with a capacity of 720 KB.

In 1984, IBM introduced the high-density 1.2 MB disk in its PC AT, but by the time of the launch of the PS/2 line in 1987 moved to 3.5-inch floppy disks, as Apple had already done with its Macintosh line in 1984. By 1988 the 3.5-inch was outselling it, and by the mid-1990s the 5.25-inch disk had virtually disappeared, and there was no option to purchase Windows 95 on 5.25-inch disks.

All disks were coated on both sides whether single or double-sided, but only double-sided disks were certified error-free on both sides of the media. However, it was possible to use both sides of a single-sided disk in single-sided drives, by making or buying so-called ‘flippy’ disks. More expensive dual-head drives which could read both sides of the disk without turning it over were later produced, and eventually became used universally.

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Preservation / Migration

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5.25-inch magneto-optical disc (1985 – 2000s)

Magneto-optical (MO) discs were a form of optical disc used for data storage, released commercially in 1985.

The disc consists of a ferromagnetic material sealed beneath a plastic coating. The only physical contact is during recording when a magnetic head is brought into contact with the side of the disc opposite to the laser. By default, MO drives verify information after writing it to the disc, and are able to immediately report any problems to the operating system. This means writing can actually take three times longer than reading, but it makes the media extremely reliable. MO discs are housed in a caddy for protection from dust.

The 5.25-inch discs were available in capacities from 256 MB to 9.2 GB, split over two sides. The drives used the SCSI interface, and mainly saw use in corporate storage and retrieval, such as legal document storage and medical imaging where high reliability, long life, and (at the time) high storage capacity were required. Optical libraries were available to automate loading and storing of the disks.

Their first major use was in the NeXT Computer in 1987, which initally offered a 256 MB 5.25-inch MO drive.

The 3.5-inch MO discs were single-sided, with capacities ranging from 128 MB to 1.3 GB. They were available with different interfaces such as SCSI, IDE and USB and were more popular with consumers.

As with all removable storage media, the advent of cheap CD/DVD drives and flash memory has made them largely redundant. Magneto-optical disks in particular were expensive when new, and while highly reliable, the slow writing time also was a drawback.

As of 2010, MO drives were no longer being manufactured.

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Apple FileWare / Twiggy Disk (1983 – 1984)

FileWare disks (commonly known as Twiggy disks after the very thin 1960s fashion model) were a type of floppy disk for data storage, and were introduced by Apple in 1983 for use in the Apple Lisa computer. They were initially intended for use in the Apple III, Lisa and Macintosh computers, but the Apple III was launched in 1981 with a standard 5.25-inch minifloppy disk drive, offering 140 KB, and the Macintosh was launched in 1984 with a single-sided 3.5-inch microfloppy disk offering 400 KB. A prototype Macintosh was produced with a FileWare drive, but this was dropped before launch. In the end, the only computer to use the FileWare drive was the Apple Lisa I, launched in 1983 and aimed at the business market. Despite being far ahead of its time in number of respects, not least for being the first widely available computer with a graphical user interface, the Apple Lisa was commercially unsuccessful.

Apple had already built its own drive controller for the Apple II, designed by Steve Wozniak, and the logical next step seemed to be to design its own drive so it could continue the boast that anything ‘Not Invented Here’ was not worth using.

The disks are very similar (but incompatible with) the Shugart designed 5.25-inch minifloppy disk and share the same dimensions. FileWare drives use two heads on either side of the spindle, and these are opposed by foam pressure pads, in an attempt to reduce wear. The outer jacket has different cut-outs to a standard 5.25- inch floppy disk, with two read slots. The write protect cutout is also in a different location, and there was a corner cutout to enable the drive to lock the disk in place since like Macintosh drives, the software ejects the disk only when it is ready to do so.

By using double-sided media, a higher track pitch, variable motor speed, and GCR recording, Apple achieved a formatted storage capacity of 871 KB per disk, compared to the 140 KB of the Disk II and 360 KB on the IBM PC. By the following year however, the IBM PC AT had a 5.25-inch disk drive offering 1.2 MB. It has been reported that modifying the outer jacket of a 1.2 MB disk will enable it to be read by a FileWare drive, but it does not increase the capacity.

FileWare drives proved to be somewhat unreliable in use and in early 1984 Apple introduced the Lisa 2, which used a single 400 KB 3.5-inch microfloppy disk drive in place of the two FileWare drives of the original Lisa. A free upgrade was offered to Lisa 1 owners, requiring owners to send back their FileWare drives and the Lisa faceplate to get the replacement drive, so Lisa I models are fairly rare, as are the disks. Only 1,000 Lisa 1 models we sold (due in part to the $10,000 price tag), and many of these were upgraded to Lisa 2.

In 1984, Apple shareholders brought a lawsuit against the company alleging that they knew about the unreliability of the drives in 1982 but continued to launch them in the Lisa despite internal memos warning of the high failure rate. The judgement went against two Apple executives in 1991, but was subsequently overturned.

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