History of the floppy disk

Over the history of the floppy disk a number of different formats were used. Floppy disks have now been largely superseded by other storage mediums and by file transfer using email.

Main article: Floppy disk

Origins, the 8-inch disk

See also: Table of 8-inch floppy formats

Drawings from IBM Floppy Disk Drive Patents

In 1967, IBM gave their San Jose, California storage development center a task to develop a simple and inexpensive system for loading microcode into their System/370 mainframes. The 370 was the first IBM computer to use read/write semiconductor memory for microcode, and whenever the power was turned off the microcode had to be reloaded (System/370's predecessor, System/360, used non-volatile read-only memory for microcode). Normally this task would be done with tape drives which almost all 370 systems included, but tapes were large and slow. IBM wanted something faster and lighter that could also be sent out to customers with software updates for $5.

IBM Direct Access Storage Product Manager Alan Shugart assigned the job to David Noble, who tried to develop a new-style tape for the purpose, but without success. Noble's team developed a read-only, 8-inch diameter flexible diskette they called the "memory disk", holding 80 kilobytes. The original disk was bare, but dirt became a serious problem so they enclosed it in a plastic envelope lined with fabric that would remove dust particles. IBM introduced the diskette commercially in 1971 ^[1][2] .

The new device, developed under the code name Minnow and shipped as the 23FD, was a standard part of System 370 processing units. It also was used as a program load device for other IBM products such as the 2835 Storage Control Unit.^[3]

Alan Shugart left IBM and moved to Memorex where his team in 1972 shipped Memorex 650, the first read-write floppy disk drive. The 650 had a data capacity of 175 kB, with 50 tracks, 8 sectors per track, and 448 bytes per sector. The Memorex disk was "hard-sectored", that is, it contained 8 sector holes (plus one index hole) at the outer diameter (outside data track 00) to synchronize the beginning of each data sector and the beginning of a track.

In 1973 IBM shipped its first read/write floppy disk drive as a part of the 3740 Data Entry System. The new system used a different recording format that stored up to 250¼ kB on the same disks. Drives supporting this format were offered by a number of manufacturers and soon became common for moving smaller amounts of data. This disk format became known as the Single Sided Single Density or SSSD format. It was designed to hold just as much data as one box of punch cards. The disk was divided into 77 tracks of 26 sectors, each holding 128 bytes. Note that 77 × 26 = 2002 sectors, whereas a box of punch cards held 2000 cards.

8-inch disk drive with diskette (3½" disk for comparison)

When the first microcomputers were being developed in the 1970s, the 8-inch floppy found a place on them as one of the few "high speed, mass storage" devices that were even remotely affordable to the target market (individuals and small businesses). The first microcomputer operating system, CP/M, originally shipped on 8-inch disks. However, the drives were still expensive, typically costing more than the computer they were attached to in early days, so most machines of the era used cassette tape instead.

Also in 1973, Shugart founded Shugart Associates which went on to become the dominant manufacturer of 8-inch FDD's. Its SA800 became the industry standard for form factor and interface.

Burroughs Corporation, meanwhile, was developing a high-performance dual-sided 8-inch drive at their Glenrothes, Scotland factory. With a capacity of 1 MB (2²⁰ B), this unit exceeded IBM's SSSD drive capacity by 4 times, and was able to provide enough space to run all the software and store data on the new Burrough's B80 data entry system, which incidentally had the first VLSI disk controller in the industry. The dual-sided 1 MB floppy entered production in 1975, but was plagued by an industry problem, poor media quality.

There were few tools available to test media for 'bit-shift' on the inner tracks, which made for high error rates and the result was a substantial investment by Burroughs in a media tester designed by Dr Nigel Mackintosh (who later made important contributions to the science of disk drive testing using Phase Margin Analysis) that they then gave to media makers as a quality control tool, leading to a vast improvement in yields.^{[dubious – discuss]} This began to change with the acceptance of the first standard for the floppy disk, ECMA-54, authored by Jim O'Reilly of Burroughs, Helmuth Hack of BASF and others. O'Reilly set a record for maneuvering this document through ECMA's approval process, with the standards sub-committee being formed in one meeting of ECMA, and approval of a draft standard in the next meeting three months later. This standard later formed the basis for the ANSI standard too. Standardization brought together a variety of competitors to make media to a single interchangeable standard, and allowed rapid quality and cost improvement.^{[dubious – discuss]}

In 1976 IBM introduced the 500 KB Double Sided Single Density (DSSD) format, and in 1977 IBM introduced the 1-1.2 MB Double Sided Double Density (DSDD) Format.^[4]

The 5¼-inch minifloppy

A double-density 5¼-inch disk with a partly exposed magnetic medium spun about a central hub. The cover has a cloth liner to brush dust from the medium. Note the “write-enable slot” to the upper right and the strobe hole next to the hub that regulates drive speed.

In 1976 two of Shugart Associates’s employees, Jim Adkisson and Don Massaro, were approached by An Wang of Wang Laboratories, who felt that the 8-inch format was simply too large for the desktop word processing machines he was developing at the time. After meeting in a bar in Boston, Adkisson asked Wang what size he thought the disks should be, and Wang pointed to a napkin and said “about that size”. Adkisson and Massaro took the napkin back to California, found it to be 5¼-inches wide, and developed a new drive of this size storing 98.5 KB later increased to 110 KB by adding 5 tracks.^[5][6] The 5¼-inch drive was considerably less expensive than 8-inch drives from IBM, and soon started appearing on CP/M machines. At one point Shugart was producing 4,000 drives a day. By 1978 there were more than 10 manufacturers producing 5¼-inch floppy drives, in competing physical disk formats: hard-sectored (90 KB) and soft-sectored (110 KB). The 5¼-inch formats quickly displaced the 8-inch for most applications, and the 5¼-inch hard-sectored disk format eventually disappeared.

These early drives read only one side of the disk, leading to the popular budget approach of cutting a second write-enable slot and index hole into the carrier envelope and flipping it over (thus, the “flippy disk”) to use the other side for additional storage. This was considered risky by some, the reasoning being that when flipped the disk would spin in the opposite direction inside its cover, so some of the dirt that had been collected by the fabric lining in the previous rotations would be picked up by the disk and dragged past the read/write head.^{[citation needed]} In reality, since some single-head floppy drives had their read/write heads on the bottom and some had them on the top, disk manufacturers routinely certified both sides of disks for use, thus the method was perfectly safe.

Tandon introduced a double-sided drive in 1978, doubling the capacity, and a new “double density” format increased it again, to 360 KB.^[7]

For most of the 1970s and 1980s the floppy drive was the primary storage device for word processors and microcomputers. Since these machines had no hard drive, the OS was usually booted from one floppy disk, which was then removed and replaced by another one containing the application. Some machines using two disk drives (or one dual drive) allowed the user to leave the OS disk in place and simply change the application disks as needed, or to copy data from one floppy to another. In the early 1980s, “quad density” 96-track-per-inch drives appeared, increasing the capacity to 720 KB. Another proprietary format was used by Digital Equipment Corporation's Rainbow-100, DECmate-II and Pro-350. It held 400 KB^[8] on a single side by using 96 tracks per inch and cramming 10 sectors per track.

White 5.25-inch floppy disk.

Despite the available capacity of the disks, support on the most popular operating system of the early 80s—PC-DOS and MS-DOS—lagged slightly behind. In fact, the original IBM PC did not include a floppy drive at all as standard equipment—you could either buy the optional 5¼-inch floppy drive or rely upon the cassette port. With version 1.0 of DOS (1981) only single sided 160 KB floppies were supported. Version 1.1 the next year saw support expand to double-sided, 320 KB disks. Finally in 1983 DOS 2.0 supported 9 sectors per track rather than 8, providing 180 KB on a (formatted) single-sided disk and 360 KB on a double-sided.^[9] Along with this change came support for different directories on the disk (now commonly called folders), which came in handy when organizing the greater number of files possible in this increased space.

In 1984, along with the IBM PC/AT, the high density disk appeared, which used 96 tracks per inch combined with a higher density magnetic media to provide 1,200 KB^[10] of storage (formally referred to as 1.2 megabytes). Since the usual (very expensive) hard disk held 10–20 megabytes at the time, this was considered quite spacious. High-density drives could also read and write to double-density disks, allowing an easy upgrade path.

Except for labelling, 5¼-inch high-density disks were externally identical to their double-density counterparts. This led to an odd situation wherein the drive itself was unable to determine the density of the disk inserted except by reading the disk media to determine the format. It was therefore possible to use a high-density drive to format a double-density disk to the higher capacity. This usually appeared to work (sometimes reporting a small number of bad sectors) — at least for a time. The problem was that the high-density format was made possible by the creation of a new high-coercivity oxide coating (after soft-sector formatting became standard, previous increases in density were largely enabled by improvements in head technology; up until that point, the media formulation had essentially remained the same since 1976). In order to format or write to this high-coercivity media, the high-density drive switched its heads into a mode using a stronger magnetic field. When these stronger fields were written onto a double-density disk (having lower coercivity media), the strongly magnetized oxide particles would begin to affect the magnetic charge of adjacent particles. The net effect is that the disk would literally begin to erase itself. On the other hand, the opposite procedure (attempting to format an HD disk as DD) would fail almost every time, as the high-coercivity media would not retain data written by the low-power DD field. High-density 3½-inch disks avoided this problem by the addition of a hole in the disk cartridge so that the drive could determine the appropriate density.

By the end of the 1980s, the 5¼-inch disks had been superseded by the 3½-inch disks. Though 5¼-inch drives were still available, as were disks, they faded in popularity as the 1990s began. The main community of users was primarily those who still owned '80s legacy machines (PCs running MS-DOS or home computers) that had no 3½-inch drive; the advent of Windows 95 (not even sold in stores in a 5¼-inch version; a coupon had to be obtained and mailed in) and subsequent phaseout of standalone MS-DOS with version 6.22 forced many of them to upgrade their hardware. On most new computers the 5¼-inch drives were optional equipment. By the mid-1990s the drives had virtually disappeared as the 3½-inch disk became the predominant floppy disk.

The "Twiggy" disk

During the development of the Apple Lisa, Apple developed a disk format codenamed Twiggy, and officially known as FileWare. While basically similar to a standard 5¼-inch disk, the Twiggy disk had an additional set of write windows on the top of the disk with the label running down the side. The drive was also present in prototypes of the original Apple Macintosh computer, but was removed in both the Mac and later versions of the Lisa in favor of the 3½-inch floppy disk from Sony. The drives were notoriously unreliable and Apple was criticized for needlessly diverging from industry standards.^[11]

3½-inch format

3-inch Quick Disk packaged as Nintendo Famicom Disk

A Smith Corona DataDisk 2.8-inch.

A 3.25-inch floppy disk.

Close-up of 3½-inch disk

Standard 3½ with a blank label

The basic internal components:
1. Write-protect tab
2. Hub
3. Shutter
4. Plastic housing
5. Paper ring
6. Magnetic disk
7. Disk sector.

Throughout the early 1980s the limitations of the 5¼-inch format were starting to become clear. Originally designed to be smaller and more practical than the 8-inch format, the 5¼-inch system was itself too large, and as the quality of the recording media grew, the same amount of data could be placed on a smaller surface. Another problem was that the 5¼-inch disks were simply scaled down versions of the 8-inch disks, which had never really been engineered for ease of use. The thin folded-plastic shell allowed the disk to be easily damaged through bending, and allowed dirt to get onto the disk surface through the opening.

A number of solutions were developed, with drives at 2-inch, 2½-inch, 3-inch and 3½-inch (50, 60, 75 and 90 mm) all being offered by various companies. They all shared a number of advantages over the older format, including a small form factor and a rigid case with a slideable write protect catch. The almost-universal use of the 5¼-inch format made it very difficult for any of these new formats to gain any significant market share.

Some of these formats included the 3-inch BRG MCD-1 developed in 1973 by Marcell Jánosi, a Hungarian inventor of Budapest Radiotechnic Company (Budapesti Rádiótechnikai Gyár - BRG).^[12], the AmDisk-3 Micro-Floppy-disk cartridge system in December 1982, ^[13][14], Mitsumi's Quick Disk 3-inch floppies, Dysan and Shugart's 3.25-inch floppy disk, and the now-ubiquitous Sony 3.5" disk.

Sony introduced their own small-format 90.0 mm × 94.0 mm disk, similar to the others but somewhat simpler in construction than the AmDisk. The first computer to use this format was Sony's SMC 70^[15] of 1982. Other than Hewlett-Packard's HP-150 of 1983 and Sony's MSX computers that year, this format suffered from a similar fate as the other new formats; the 5¼-inch format simply had too much market share. Things changed dramatically when in 1982 the Microfloppy Industry Committee, a consortium ultimately of 23 media companies, agreed upon a 3½-inch media specification based upon but differing from the original Sony design^[16]. The first drives compatible with this new media specification were shipped in early 1983^[17]. In 1984 Apple Computer selected the format for their new Macintosh computers, in 1985 Atari for their new ST line and Commodore for their new Amiga. By 1988 the 3½-inch was outselling the 5¼-inch^[18].

Note that the term "3½-inch" or "3.5 inch" disk was primarily targeted at the non-metric US market and was rounded from the actual metric size of 90 mm used internationally.

The 3½-inch disks had, by way of their rigid case's slide-in-place metal cover, the significant advantage of being much better protected against unintended physical contact with the disk surface than 5¼-inch disks when the disk was handled outside the disk drive. When the disk was inserted, a part inside the drive moved the metal cover aside, giving the drive's read/write heads the necessary access to the magnetic recording surfaces. Adding the slide mechanism resulted in a slight departure from the previous square outline. The irregular, rectangular shape had the additional merit that it made it impossible to insert the disk sideways by mistake as had indeed been possible with earlier formats.

The shutter mechanism was not without its problems, however. On old or roughly treated disks the shutter could bend away from the disk. This made it vulnerable to being ripped off completely (which does not damage the disk itself but does leave it much more vulnerable to dust), or worse, catching inside a drive and possibly either getting stuck inside or damaging the drive.

Like the 5¼-inch, the 3½-inch disk underwent an evolution of its own. When Apple introduced the Macintosh in 1984, it used single-sided 3½-inch disk drives with an advertised capacity of 400 kB. The encoding technique used by these drives was known as GCR, or Group Code Recording (similar recording methods were used by Commodore on its 5 1/4 inch drives and Sirius Computer in its Victor 9000 non PC compatible MS-Dos machine). Somewhat later, PC-compatible machines began using single-sided 3½-inch disks with an advertised capacity of 360 kB (the same as a single-sided 5¼-inch disk), and a different, incompatible recording format called MFM (Modified Frequency Modulation). GCR and MFM drives (and their formatted disks) were incompatible, although the physical disks were the same. In 1986, Apple introduced double-sided, 800 kB disks, still using GCR, and around the same time, 720 kB double-sided double-density MFM disks began to appear on PC-compatibles.^{[citation needed]}

A newer and better, MFM-based, "high-density" format, displayed as "HD" on the disks themselves and storing 1440 kB of data, was introduced in 1987. These HD disks had an extra hole in the case on the opposite side of the write-protect notch. IBM used this format on their PS/2 series introduced in 1987. Apple started using "HD" in 1988, on the Macintosh IIx, and the HD floppy drive soon became universal on virtually all Macintosh and PC hardware. Apple's FDHD (Floppy Disk High Density) drive was capable of reading and writing both GCR and MFM formatted disks, and thus made it relatively easy to exchange files with PC users. Apple later marketed this drive as the SuperDrive. Interestingly, Apple began using the SuperDrive brand name again around 2003 to denote their all-formats CD/DVD reader/writer.^{[citation needed]}

Besides Sony, Apple was the first major manufacturer to start selling computers with 3½-inch disk drives as well as the first to stop shipping those in 1998 with introduction of iMac.

Another advance in the oxide coatings allowed for a new "extended-density" ("ED") format at 2880 kB introduced on the second generation NeXT Computers in 1991, and on IBM PS/2 model 57 also in 1991, but by the time it was available it was already too small in capacity to be a useful advance over the HD format and never became widely used. The 3½-inch drives sold more than a decade later still use the same 1.44 MB HD format that was standardized in 1989, in ISO 9529-1,2.

References