Split (1)

train · 7.61k rows

Number int64 1 7.61k	Text stringlengths 2 3.11k
3,301	Some early optical drives have dedicated buttons for CD playback controls on their front panel, allowing them to act as a standalone compact disc player.
3,302	External drives were popular in the beginning, because the drives often required complex electronics to institute, rivaling in complexity the Host computer system itself. External drives using SCSI, Parallel port, USB and FireWire interfaces exist, most modern drives being USB. Some portable versions for laptops power themselves from batteries or directly from their interface bus.
3,303	Drives with a SCSI interface were originally the only system interface available, but they never became popular in the price sensitive low-end consumer market which constituted majority of the demand. They were less common and tended to be more expensive, because of the cost of their interface chipsets, more complex SCSI connectors, and small volume of sales in comparison to proprietary cost-reduced applications, but most importantly because most consumer market computer systems did not have any sort of SCSI interface in them the market for them was small. However, support for multitude of various cost-reduced proprietary optical drive bus standards were usually embedded with sound cards which were often bundled with the optical drives themselves in the early years. Some sound card and optical drive bundles even featured a full SCSI bus. Modern IDE/ATAPI compliant Parallel ATA and Serial ATA drive control chipsets and their interface technology is more complex to manufacture than a traditional 8bit 50Mhz SCSI drive interface, because they feature properties of both the SCSI and ATA bus, but are cheaper to make overall due to economies of scale.
3,304	When the optical disc drive was first developed, it was not easy to add to computer systems. Some computers such as the IBM PS/2 were standardizing on the 3+1⁄2-inch floppy and 3+1⁄2-inch hard disk and did not include a place for a large internal device. Also IBM PCs and clones at first only included a single ATA drive interface, which by the time the CD-ROM was introduced, was already being used to support two hard drives and were completely incapable of supporting removable media, a drive falling off or being removed from the bus while the system was live, would cause an unrecoverable error and crash the entire system. Early consumer grade laptops simply had no built-in high-speed interface for supporting an external storage device. High-end workstation systems and laptops featured a SCSI interface which had a standard for externally connected devices.
3,305	This was solved through several techniques:
3,306	Due to lack of asynchrony in existing implementations, an optical drive encountering damaged sectors may cause computer programs trying to access the drives, such as Windows Explorer, to lock up.
3,307	Drive models may support adjustment of behavioural parameters for performance optimization and testing purposes, such as the read retry count , write retry count , and the option to deactivate error correction . For example, the read retry count specifies how often the drive should attempt reading a damaged sector. A higher value may increase the chance of successfully reading individual damaged sectors, but at the expense of responsiveness, since it adds delays during which the device seems unresponsive to the computer.
3,308	The sdparm command-line utility allows manually controlling such parameters. For example, sdparm --set RRC=10 /dev/sr0 sets the read retry count to 10 for the optical drive device file "sr0", and sdparm --all /dev/sr0 lists all code pages. The values may be interpreted varyingly among drive models or vendors.
3,309	The optical drives in the photos are shown right side up; the disc would sit on top of them. The laser and optical system scans the underside of the disc.
3,310	With reference to the top photo, just to the right of image center is the disc motor, a metal cylinder, with a gray centering hub and black rubber drive ring on top. There is a disc-shaped round clamp, loosely held inside the cover and free to rotate; it's not in the photo. After the disc tray stops moving inward, as the motor and its attached parts rise, a magnet near the top of the rotating assembly contacts and strongly attracts the clamp to hold and center the disc. This motor is an "outrunner"-style brushless DC motor which has an external rotor – every visible part of it spins.
3,311	Two parallel guide rods that run between upper left and lower right in the photo carry the "sled", the moving optical read-write head. As shown, this "sled" is close to, or at the position where it reads or writes at the edge of the disc. To move the "sled" during continuous read or write operations, a stepper motor rotates a leadscrew to move the "sled" throughout its total travel range. The motor, itself, is the short gray cylinder just to the left of the most-distant shock mount; its shaft is parallel to the support rods. The leadscrew is the rod with evenly-spaced darker details; these are the helical grooves that engage a pin on the "sled".
3,312	In contrast, the mechanism shown in the second photo, which comes from a cheaply made DVD player, uses less accurate and less efficient brushed DC motors to both move the sled and spin the disc. Some older drives use a DC motor to move the sled, but also have a magnetic rotary encoder to keep track of the position. Most drives in computers use stepper motors.
3,313	The gray metal chassis is shock-mounted at its four corners to reduce sensitivity to external shocks, and to reduce drive noise from residual imbalance when running fast. The soft shock mount grommets are just below the brass-colored screws at the four corners .
3,314	In the third photo, the components under the cover of the lens mechanism are visible. The two permanent magnets on either side of the lens holder as well as the coils that move the lens can be seen. This allows the lens to be moved up, down, forwards, and backwards to stabilize the focus of the beam.
3,315	In the fourth photo, the inside of the optics package can be seen. Note that since this is a CD-ROM drive, there is only one laser, which is the black component mounted to the bottom left of the assembly. Just above the laser are the first focusing lens and prism that direct the beam at the disc. The tall, thin object in the center is a half-silvered mirror that splits the laser beam in multiple directions. To the bottom right of the mirror is the main photodiode that senses the beam reflected off the disc. Above the main photodiode is a second photodiode that is used to sense and regulate the power of the laser.
3,316	The irregular orange material is flexible etched copper foil supported by thin sheet plastic; these are "flexible circuits" that connect everything to the electronics .
3,317	The first laser disc, demonstrated in 1972, was the Laservision 12-inch video disc. The video signal was stored as an analog format like a video cassette. The first digitally recorded optical disc was a 5-inch audio compact disc in a read-only format created by Sony and Philips in 1975.
3,318	The first erasable optical disc drives were announced in 1983, by Matsushita , Sony, and Kokusai Denshin Denwa . Sony eventually released the first commercial erasable and rewritable 5+1⁄4-inch optical disc drive in 1987, with dual-sided discs capable of holding 325 MB per side.
3,319	The CD-ROM format was developed by Sony and Denon, introduced in 1984, as an extension of Compact Disc Digital Audio and adapted to hold any form of digital data. The CD-ROM format has a storage capacity of 650 MB. Also in 1984, Sony introduced a LaserDisc data storage format, with a larger data capacity of 3.28 GB.
3,320	In September 1992, Sony announced the MiniDisc format, which was supposed to combine the audio clarity of CD's and the convenience of a cassette size. The standard capacity holds 80 minutes of audio. In January 2004, Sony revealed an upgraded Hi-MD format, which increased the capacity to 1 GB .
3,321	The DVD format, developed by Panasonic, Sony, and Toshiba, was released in 1995, and was capable of holding 4.7 GB per layer; with the first DVD players shipping on November 1, 1996, by Panasonic and Toshiba in Japan and the first DVD-ROM compatible computers being shipped on November 6 of that year by Fujitsu. Sales of DVD-ROM drives for computers in the U.S. began on March 24, 1997, when Creative Labs released their PC-DVD kit to the market.
3,322	In 1999, Kenwood released a multi-beam optical drive that achieved burning speeds as high as 72×, which would require dangerous spinning speeds to attain with single-beam burning. However, it suffered from reliability issues.
3,323	The first Blu-ray prototype was unveiled by Sony in October 2000, and the first commercial recording device was released to market on April 10, 2003. In January 2005, TDK announced that they had developed an ultra-hard yet very thin polymer coating for Blu-ray Discs; this was a significant technical advance because better protection was desired for the consumer market to protect bare discs against scratching and damage compared to DVD. Technically Blu-ray Disc also required a thinner layer for the narrower beam and shorter wavelength 'blue' laser. The first BD-ROM players were shipped in mid-June 2006. The first Blu-ray Disc titles were released by Sony and MGM on June 20, 2006. The first mass-market Blu-ray Disc rewritable drive for the PC was the BWU-100A, released by Sony on July 18, 2006.
3,324	Starting in the mid-2010s, computer manufacturers began to stop including built-in optical disc drives on their products, with the advent of cheap, rugged , fast and high capacity USB drives and video on demand over the internet. Excluding an optical drive allows for circuit boards in laptops to be larger and less dense, requiring less layers, reducing production costs while also reducing weight and thickness, or for batteries to be larger. Computer case manufacturers also began to stop including 5+1⁄4-inch bays for installing optical disc drives. However, new optical disc drives are still available for purchase. Notable optical disc drive OEMs include Hitachi, LG Electronics , Toshiba, Samsung Electronics , Sony, NEC , Lite-On, Philips , Pioneer Corporation, Plextor, Panasonic, Yamaha Corporation and Kenwood.
3,325	Most optical drives are backward compatible with their ancestors up to CD, although this is not required by standards.
3,326	Compared to a CD's 1.2 mm layer of polycarbonate, a DVD's laser beam only has to penetrate 0.6 mm in order to reach the recording surface. This allows a DVD drive to focus the beam on a smaller spot size and to read smaller pits. DVD lens supports a different focus for CD or DVD media with same laser. With the newer Blu-ray Disc drives, the laser only has to penetrate 0.1 mm of material. Thus the optical assembly would normally have to have an even greater focus range. In practice, the Blu-ray optical system is separate from the DVD/CD system.
3,327	During the times of CD writer drives, they are often marked with three different speed ratings. In these cases, the first speed is for write-once operations, the second speed for re-write operations, and the last speed for read-only operations. For example, a 40×/16×/48× CD writer drive is capable of writing to CD-R media at speed of 40× , writing to CD-RW media at speed of 16× , and reading from a CD-ROM media at speed of 48× .
3,328	During the times of combo drives, an additional speed rating is designated for DVD-ROM media reading operations.
3,329	For DVD writer drives, Blu-ray Disc combo drives, and Blu-ray Disc writer drives, the writing and reading speed of their respective optical media are specified in its retail box, user's manual, or bundled brochures or pamphlets.
3,330	In the late 1990s, buffer underruns became a very common problem as high-speed CD recorders began to appear in home and office computers, which—for a variety of reasons—often could not muster the I/O performance to keep the data stream to the recorder steadily fed. The recorder, should it run short, would be forced to halt the recording process, leaving a truncated track that usually renders the disc useless.
3,331	In response, manufacturers of CD recorders began shipping drives with "buffer underrun protection" . These can suspend and resume the recording process in such a way that the gap the stoppage produces can be dealt with by the error-correcting logic built into CD players and CD-ROM drives. The first of these drives were rated at 12× and 16×.
3,332	The first optical drive to support recording DVDs at 16× speed was the Pioneer DVR-108, released in the second half of 2004. At that time however, no recordable DVD media supported that high recording speed yet.
3,333	While drives are burning DVD+R, DVD+RW and all Blu-ray formats, they do not require any such error correcting recovery as the recorder is able to place the new data exactly on the end of the suspended write effectively producing a continuous track . Although later interfaces were able to stream data at the required speed, many drives now write in a 'zoned constant linear velocity' . This means that the drive has to temporarily suspend the write operation while it changes speed and then recommence it once the new speed is attained. This is handled in the same manner as a buffer underrun.
3,334	The internal buffer of optical disc writer drives is: 8 MiB or 4 MiB when recording BD-R, BD-R DL, BD-RE, or BD-RE DL media; 2 MiB when recording DVD-R, DVD-RW, DVD-R DL, DVD+R, DVD+RW, DVD+RW DL, DVD-RAM, CD-R, or CD-RW media.
3,335	CD recording on personal computers was originally a batch-oriented task in that it required specialised authoring software to create an "image" of the data to record and to record it to disc in the one session. This was acceptable for archival purposes, but limited the general convenience of CD-R and CD-RW discs as a removable storage medium.
3,336	Packet writing is a scheme in which the recorder writes incrementally to disc in short bursts, or packets. Sequential packet writing fills the disc with packets from bottom up. To make it readable in CD-ROM and DVD-ROM drives, the disc can be closed at any time by writing a final table-of-contents to the start of the disc; thereafter, the disc cannot be packet-written any further. Packet writing, together with support from the operating system and a file system like UDF, can be used to mimic random write-access as in media like flash memory and magnetic disks.
3,337	Fixed-length packet writing divides up the disc into padded, fixed-size packets. The padding reduces the capacity of the disc, but allows the recorder to start and stop recording on an individual packet without affecting its neighbours. These resemble the block-writable access offered by magnetic media closely enough that many conventional file systems will work as-is. Such discs, however, are not readable in most CD-ROM and DVD-ROM drives or on most operating systems without additional third-party drivers. The division into packets is not as reliable as it may seem as CD-R and DVD-R drives can only locate data to within a data block. Although generous gaps are left between blocks, the drive nevertheless can occasionally miss and either destroy some existing data or even render the disc unreadable.
3,338	The DVD+RW disc format eliminates this unreliability by embedding more accurate timing hints in the data groove of the disc and allowing individual data blocks to be replaced without affecting backward compatibility . The format itself was designed to deal with discontinuous recording because it was expected to be widely used in digital video recorders. Many such DVRs use variable-rate video compression schemes which require them to record in short bursts; some allow simultaneous playback and recording by alternating quickly between recording to the tail of the disc whilst reading from elsewhere. The Blu-ray Disc system also encompasses this technology.
3,339	Mount Rainier aims to make packet-written CD-RW and DVD+RW discs as convenient to use as that of removable magnetic media by having the firmware format new discs in the background and manage media defects . As of February 2007, support for Mount Rainier is natively supported in Windows Vista. All previous versions of Windows require a third-party solution, as does Mac OS X.
3,340	Owing to pressure from the music industry, as represented by the IFPI and RIAA, Philips developed the Recorder Identification Code to allow media to be uniquely associated with the recorder that has written it. This standard is contained in the Rainbow Books. The RID-Code consists of a supplier code , a model number and the unique ID of the recorder. Quoting Philips, the RID "enables a trace for each disc back to the exact machine on which it was made using coded information in the recording itself. The use of the RID code is mandatory."
3,341	Although the RID was introduced for music and video industry purposes, the RID is included on every disc written by every drive, including data and backup discs. The value of the RID is questionable as it is impossible to locate any individual recorder due to there being no database.
3,342	The Source Identification Code is an eight character supplier code that is placed on optical discs by the manufacturer. The SID identifies not only manufacturer, but also the individual factory and machine that produced the disc.
3,343	According to Phillips, the administrator of the SID codes, the SID code provides an optical disc production facility with the means to identify all discs mastered or replicated in its plant, including the specific Laser Beam Recorder signal processor or mould that produced a particular stamper or disc.
3,344	The standard use of RID and SID mean that each disc written contains a record of the machine that produced a disc , and which drive wrote it . This combined knowledge may be very useful to law enforcement, to investigative agencies, and to private or corporate investigators.
3,345	A significant motivation for introducing the SID code was to identify disc manufacturing plants producing unauthorised copies of commercial CDs. By the 1990s, the production process for CDs had evolved from requiring a "clean-room" environment involving multiple processes, this demanding a substantial investment and likely to be confined to "responsible" organisations, into an activity that could be undertaken with "mono-liner" equipment, this having been developed in the late 1980s and capable of packaging "the whole process into a single box" that could occupy "no more space than a couple of office desks". Consequently, the CD manufacturing industry had grown to include less reputable organisations and, by 1994, could produce a volume of discs twice that of the estimated demand for "legitimate CDs", with music industry organisations claiming that illicit copies were outselling legitimate copies by significant margins in some markets. Philips and the IFPI envisaged that combinations of codes, each identifying a disc mastering establishment and the manufacturing plant used to make a particular disc, would assist in identifying those responsible for illicit CD production. However, the scheme relied on existing manufacturing plants upgrading their equipment to support the introduction of this measure, and the accompanying challenge of convincing such facilities was perceived as "a little difficult" in cases where those facilities were already involved in making considerable numbers of illicit discs.
3,346	A floppy disk or floppy diskette is a type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined with a fabric that removes dust particles from the spinning disk. Floppy disks store digital data which can be read and written when the disk is inserted into a floppy disk drive connected to or inside a computer or other device.
3,347	The first floppy disks, invented and made by IBM, had a disk diameter of 8 inches . Subsequently, the 5¼-inch and then the 3½-inch became a ubiquitous form of data storage and transfer into the first years of the 21st century. 3½-inch floppy disks can still be used with an external USB floppy disk drive. USB drives for 5¼-inch, 8-inch, and other-size floppy disks are rare to non-existent. Some individuals and organizations continue to use older equipment to read or transfer data from floppy disks.
3,348	Floppy disks were so common in late 20th-century culture that many electronic and software programs continue to use save icons that look like floppy disks well into the 21st century, as a form of skeuomorphic design. While floppy disk drives still have some limited uses, especially with legacy industrial computer equipment, they have been superseded by data storage methods with much greater data storage capacity and data transfer speed, such as USB flash drives, memory cards, optical discs, and storage available through local computer networks and cloud storage.
3,349	The first commercial floppy disks, developed in the late 1960s, were 8 inches in diameter; they became commercially available in 1971 as a component of IBM products and both drives and disks were then sold separately starting in 1972 by Memorex and others. These disks and associated drives were produced and improved upon by IBM and other companies such as Memorex, Shugart Associates, and Burroughs Corporation. The term "floppy disk" appeared in print as early as 1970, and although IBM announced its first media as the Type 1 Diskette in 1973, the industry continued to use the terms "floppy disk" or "floppy".
3,350	In 1976, Shugart Associates introduced the 5¼-inch FDD. By 1978, there were more than ten manufacturers producing such FDDs. There were competing floppy disk formats, with hard- and soft-sector versions and encoding schemes such as differential Manchester encoding , modified frequency modulation , M2FM and group coded recording . The 5¼-inch format displaced the 8-inch one for most uses, and the hard-sectored disk format disappeared. The most common capacity of the 5¼-inch format in DOS-based PCs was 360 KB for the Double-Sided Double-Density format using MFM encoding. In 1984, IBM introduced with its PC/AT the 1.2 MB dual-sided 5¼-inch floppy disk, but it never became very popular. IBM started using the 720 KB double density 3½-inch microfloppy disk on its Convertible laptop computer in 1986 and the 1.44 MB high-density version with the IBM Personal System/2 line in 1987. These disk drives could be added to older PC models. In 1988, Y-E Data introduced a drive for 2.88 MB Double-Sided Extended-Density diskettes which was used by IBM in its top-of-the-line PS/2 and some RS/6000 models and in the second-generation NeXTcube and NeXTstation; however, this format had limited market success due to lack of standards and movement to 1.44 MB drives.
3,351	Throughout the early 1980s, limits of the 5¼-inch format became clear. Originally designed to be more practical than the 8-inch format, it was becoming considered too large; as the quality of recording media grew, data could be stored in a smaller area. Several solutions were developed, with drives at 2-, 2½-, 3-, 3¼-, 3½- and 4-inches disk) offered by various companies. They all had several advantages over the old format, including a rigid case with a sliding metal shutter over the head slot, which helped protect the delicate magnetic medium from dust and damage, and a sliding write protection tab, which was far more convenient than the adhesive tabs used with earlier disks. The large market share of the well-established 5¼-inch format made it difficult for these diverse mutually-incompatible new formats to gain significant market share. A variant on the Sony design, introduced in 1983 by many manufacturers, was then rapidly adopted. By 1988, the 3½-inch was outselling the 5¼-inch.
3,352	Generally, the term floppy disk persisted, even though later style floppy disks have a rigid case around an internal floppy disk.
3,353	By the end of the 1980s, 5¼-inch disks had been superseded by 3½-inch disks. During this time, PCs frequently came equipped with drives of both sizes. By the mid-1990s, 5¼-inch drives had virtually disappeared, as the 3½-inch disk became the predominant floppy disk. The advantages of the 3½-inch disk were its higher capacity, its smaller physical size, and its rigid case which provided better protection from dirt and other environmental risks.
3,354	Floppy disks became commonplace during the 1980s and 1990s in their use with personal computers to distribute software, transfer data, and create backups. Before hard disks became affordable to the general population, floppy disks were often used to store a computer's operating system . Most home computers from that time have an elementary OS and BASIC stored in read-only memory , with the option of loading a more advanced OS from a floppy disk.
3,355	By the early 1990s, the increasing software size meant large packages like Windows or Adobe Photoshop required a dozen disks or more. In 1996, there were an estimated five billion standard floppy disks in use.
3,356	An attempt to enhance the existing 3½-inch designs was the SuperDisk in the late 1990s, using very narrow data tracks and a high precision head guidance mechanism with a capacity of 120 MB and backward-compatibility with standard 3½-inch floppies; a format war briefly occurred between SuperDisk and other high-density floppy-disk products, although ultimately recordable CDs/DVDs, solid-state flash storage, and eventually cloud-based online storage would render all these removable disk formats obsolete. External USB-based floppy disk drives are still available, and many modern systems provide firmware support for booting from such drives.
3,357	In the mid-1990s, mechanically incompatible higher-density floppy disks were introduced, like the Iomega Zip disk. Adoption was limited by the competition between proprietary formats and the need to buy expensive drives for computers where the disks would be used. In some cases, failure in market penetration was exacerbated by the release of higher-capacity versions of the drive and media being not backward-compatible with the original drives, dividing the users between new and old adopters. Consumers were wary of making costly investments into unproven and rapidly changing technologies, so none of the technologies became the established standard.
3,358	Apple introduced the iMac G3 in 1998 with a CD-ROM drive but no floppy drive; this made USB-connected floppy drives popular accessories, as the iMac came without any writable removable media device.
3,359	Recordable CDs were touted as an alternative, because of the greater capacity, compatibility with existing CD-ROM drives, and—with the advent of re-writeable CDs and packet writing—a similar reusability as floppy disks. However, CD-R/RWs remained mostly an archival medium, not a medium for exchanging data or editing files on the medium itself, because there was no common standard for packet writing which allowed for small updates. Other formats, such as magneto-optical discs, had the flexibility of floppy disks combined with greater capacity, but remained niche due to costs. High-capacity backward compatible floppy technologies became popular for a while and were sold as an option or even included in standard PCs, but in the long run, their use was limited to professionals and enthusiasts.
3,360	Flash-based USB-thumb drives finally were a practical and popular replacement, that supported traditional file systems and all common usage scenarios of floppy disks. As opposed to other solutions, no new drive type or special software was required that impeded adoption, since all that was necessary was an already common USB port.
3,361	By 2002, most manufacturers still provided floppy disk drives as standard equipment to meet user demand for file-transfer and an emergency boot device, as well as for the general secure feeling of having the familiar device. By this time, the retail cost of a floppy drive had fallen to around $20 , so there was little financial incentive to omit the device from a system. Subsequently, enabled by the widespread support for USB flash drives and BIOS boot, manufacturers and retailers progressively reduced the availability of floppy disk drives as standard equipment. In February 2003, Dell, one of the leading personal computer vendors, announced that floppy drives would no longer be pre-installed on Dell Dimension home computers, although they were still available as a selectable option and purchasable as an aftermarket OEM add-on. By January 2007, only 2% of computers sold in stores contained built-in floppy disk drives.
3,362	Floppy disks are used for emergency boots in aging systems lacking support for other bootable media and for BIOS updates, since most BIOS and firmware programs can still be executed from bootable floppy disks. If BIOS updates fail or become corrupt, floppy drives can sometimes be used to perform a recovery. The music and theatre industries still use equipment requiring standard floppy disks . Industrial automation equipment such as programmable machinery and industrial robots may not have a USB interface; data and programs are then loaded from disks, damageable in industrial environments. This equipment may not be replaced due to cost or requirement for continuous availability; existing software emulation and virtualization do not solve this problem because a customized operating system is used that has no drivers for USB devices. Hardware floppy disk emulators can be made to interface floppy-disk controllers to a USB port that can be used for flash drives.
3,363	In May 2016, the United States Government Accountability Office released a report that covered the need to upgrade or replace legacy computer systems within federal agencies. According to this document, old IBM Series/1 minicomputers running on 8-inch floppy disks are still used to coordinate "the operational functions of the United States' nuclear forces". The government planned to update some of the technology by the end of the 2017 fiscal year.
3,364	Windows 10 and Windows 11 no longer come with drivers for floppy disk drives . However, they will still support them with a separate device driver provided by Microsoft.
3,365	The British Airways Boeing 747-400 fleet, up to its retirement in 2020, used 3½-inch floppy disks to load avionics software.
3,366	Sony, who had been in the floppy disk business since 1983, ended domestic sales of all six 3½-inch floppy disk models as of March 2011. This has been viewed by some as the end of the floppy disk. While production of new floppy disk media has ceased, sales and uses of this media from inventories is expected to continue until at least 2026.
3,367	For more than two decades, the floppy disk was the primary external writable storage device used. Most computing environments before the 1990s were non-networked, and floppy disks were the primary means to transfer data between computers, a method known informally as sneakernet. Unlike hard disks, floppy disks are handled and seen; even a novice user can identify a floppy disk. Because of these factors, a picture of a 3½-inch floppy disk became an interface metaphor for saving data. The floppy disk symbol is still used by software on user-interface elements related to saving files even though physical floppy disks are largely obsolete.
3,368	The 8-inch and 5¼-inch floppy disks contain a magnetically coated round plastic medium with a large circular hole in the center for a drive's spindle. The medium is contained in a square plastic cover that has a small oblong opening in both sides to allow the drive's heads to read and write data and a large hole in the center to allow the magnetic medium to spin by rotating it from its middle hole.
3,369	Inside the cover are two layers of fabric with the magnetic medium sandwiched in the middle. The fabric is designed to reduce friction between the medium and the outer cover, and catch particles of debris abraded off the disk to keep them from accumulating on the heads. The cover is usually a one-part sheet, double-folded with flaps glued or spot-welded together.
3,370	A small notch on the side of the disk identifies that it is writable, detected by a mechanical switch or phototransistor above it; if it is not present, the disk can be written; in the 8-inch disk the notch is covered to enable writing while in the 5¼-inch disk the notch is open to enable writing. Tape may be used over the notch to change the mode of the disk. Punch devices were sold to convert read-only disks to writable ones and enable writing on the unused side of single sided disks; such modified disks became known as flippy disks.
3,371	Another LED/photo-transistor pair located near the center of the disk detects the index hole once per rotation in the magnetic disk; it is used to detect the angular start of each track and whether or not the disk is rotating at the correct speed. Early 8‑inch and 5¼‑inch disks had physical holes for each sector and were termed hard sectored disks. Later soft-sectored disks have only one index hole, and sector position is determined by the disk controller or low-level software from patterns marking the start of a sector. Generally, the same drives are used to read and write both types of disks, with only the disks and controllers differing. Some operating systems using soft sectors, such as Apple DOS, do not use the index hole, and the drives designed for such systems often lack the corresponding sensor; this was mainly a hardware cost-saving measure.
3,372	The core of the 3½-inch disk is the same as the other two disks, but the front has only a label and a small opening for reading and writing data, protected by the shutter—a spring-loaded metal or plastic cover, pushed to the side on entry into the drive. Rather than having a hole in the center, it has a metal hub which mates to the spindle of the drive. Typical 3½-inch disk magnetic coating materials are:
3,373	Two holes at the bottom left and right indicate whether the disk is write-protected and whether it is high-density; these holes are spaced as far apart as the holes in punched A4 paper, allowing write-protected high-density floppies to be clipped into standard ring binders. The dimensions of the disk shell are not quite square: its width is slightly less than its depth, so that it is impossible to insert the disk into a drive slot sideways . A diagonal notch at top right ensures that the disk is inserted into the drive in the correct orientation—not upside down or label-end first—and an arrow at top left indicates direction of insertion. The drive usually has a button that, when pressed, ejects the disk with varying degrees of force, the discrepancy due to the ejection force provided by the spring of the shutter. In IBM PC compatibles, Commodores, Apple II/IIIs, and other non-Apple-Macintosh machines with standard floppy disk drives, a disk may be ejected manually at any time. The drive has a disk-change switch that detects when a disk is ejected or inserted. Failure of this mechanical switch is a common source of disk corruption if a disk is changed and the drive fails to notice.
3,374	One of the chief usability problems of the floppy disk is its vulnerability; even inside a closed plastic housing, the disk medium is highly sensitive to dust, condensation and temperature extremes. As with all magnetic storage, it is vulnerable to magnetic fields. Blank disks have been distributed with an extensive set of warnings, cautioning the user not to expose it to dangerous conditions. Rough treatment or removing the disk from the drive while the magnetic media is still spinning is likely to cause damage to the disk, drive head, or stored data. On the other hand, the 3½‑inch floppy has been lauded for its mechanical usability by human–computer interaction expert Donald Norman:
3,375	A spindle motor in the drive rotates the magnetic medium at a certain speed, while a stepper motor-operated mechanism moves the magnetic read/write heads radially along the surface of the disk. Both read and write operations require the media to be rotating and the head to contact the disk media, an action originally accomplished by a disk-load solenoid. Later drives held the heads out of contact until a front-panel lever was rotated or disk insertion was complete . To write data, current is sent through a coil in the head as the media rotates. The head's magnetic field aligns the magnetization of the particles directly below the head on the media. When the current is reversed the magnetization aligns in the opposite direction, encoding one bit of data. To read data, the magnetization of the particles in the media induce a tiny voltage in the head coil as they pass under it. This small signal is amplified and sent to the floppy disk controller, which converts the streams of pulses from the media into data, checks it for errors, and sends it to the host computer system.
3,376	A blank unformatted diskette has a coating of magnetic oxide with no magnetic order to the particles. During formatting, the magnetizations of the particles are aligned forming tracks, each broken up into sectors, enabling the controller to properly read and write data. The tracks are concentric rings around the center, with spaces between tracks where no data is written; gaps with padding bytes are provided between the sectors and at the end of the track to allow for slight speed variations in the disk drive, and to permit better interoperability with disk drives connected to other similar systems.
3,377	Each sector of data has a header that identifies the sector location on the disk. A cyclic redundancy check is written into the sector headers and at the end of the user data so that the disk controller can detect potential errors.
3,378	Some errors are soft and can be resolved by automatically re-trying the read operation; other errors are permanent and the disk controller will signal a failure to the operating system if multiple attempts to read the data still fail.
3,379	After a disk is inserted, a catch or lever at the front of the drive is manually lowered to prevent the disk from accidentally emerging, engage the spindle clamping hub, and in two-sided drives, engage the second read/write head with the media.
3,380	In some 5¼-inch drives, insertion of the disk compresses and locks an ejection spring which partially ejects the disk upon opening the catch or lever. This enables a smaller concave area for the thumb and fingers to grasp the disk during removal.
3,381	Newer 5¼-inch drives and all 3½-inch drives automatically engage the spindle and heads when a disk is inserted, doing the opposite with the press of the eject button.
3,382	On Apple Macintosh computers with built-in 3½-inch disk drives, the ejection button is replaced by software controlling an ejection motor which only does so when the operating system no longer needs to access the drive. The user could drag the image of the floppy drive to the trash can on the desktop to eject the disk. In the case of a power failure or drive malfunction, a loaded disk can be removed manually by inserting a straightened paper clip into a small hole at the drive's front panel, just as one would do with a CD-ROM drive in a similar situation. The Sharp X68000 featured soft-eject 5¼-inch drives. Some late-generation IBM PS/2 machines had soft-eject 3½-inch disk drives as well for which some issues of DOS offered an EJECT command.
3,383	Before a disk can be accessed, the drive needs to synchronize its head position with the disk tracks. In some drives, this is accomplished with a Track Zero Sensor, while for others it involves the drive head striking an immobile reference surface.
3,384	In either case, the head is moved so that it is approaching track zero position of the disk. When a drive with the sensor has reached track zero, the head stops moving immediately and is correctly aligned. For a drive without the sensor, the mechanism attempts to move the head the maximum possible number of positions needed to reach track zero, knowing that once this motion is complete, the head will be positioned over track zero.
3,385	Some drive mechanisms such as the Apple II 5¼-inch drive without a track zero sensor, produce characteristic mechanical noises when trying to move the heads past the reference surface. This physical striking is responsible for the 5¼-inch drive clicking during the boot of an Apple II, and the loud rattles of its DOS and ProDOS when disk errors occurred and track zero synchronization was attempted.
3,386	All 8-inch and some 5¼-inch drives used a mechanical method to locate sectors, known as either hard sectors or soft sectors, and is the purpose of the small hole in the jacket, off to the side of the spindle hole. A light beam sensor detects when a punched hole in the disk is visible through the hole in the jacket.
3,387	For a soft-sectored disk, there is only a single hole, which is used to locate the first sector of each track. Clock timing is then used to find the other sectors behind it, which requires precise speed regulation of the drive motor.
3,388	For a hard-sectored disk, there are many holes, one for each sector row, plus an additional hole in a half-sector position, that is used to indicate sector zero.
3,389	The Apple II computer system is notable in that it did not have an index hole sensor and ignored the presence of hard or soft sectoring. Instead, it used special repeating data synchronization patterns written to the disk between each sector, to assist the computer in finding and synchronizing with the data in each track.
3,390	The later 3½-inch drives of the mid-1980s did not use sector index holes, but instead also used synchronization patterns.
3,391	Most 3½-inch drives used a constant speed drive motor and contain the same number of sectors across all tracks. This is sometimes referred to as Constant Angular Velocity . In order to fit more data onto a disk, some 3½-inch drives instead use Constant Linear Velocity , which uses a variable speed drive motor that spins more slowly as the head moves away from the center of the disk, maintaining the same speed of the head relative to the surface of the disk. This allows more sectors to be written to the longer middle and outer tracks as the track length increases.
3,392	While the original IBM 8-inch disk was actually so defined, the other sizes are defined in the metric system, their usual names being but rough approximations.
3,393	Different sizes of floppy disks are mechanically incompatible, and disks can fit only one size of drive. Drive assemblies with both 3½-inch and 5¼-inch slots were available during the transition period between the sizes, but they contained two separate drive mechanisms. In addition, there are many subtle, usually software-driven incompatibilities between the two. 5¼-inch disks formatted for use with Apple II computers would be unreadable and treated as unformatted on a Commodore. As computer platforms began to form, attempts were made at interchangeability. For example, the "SuperDrive" included from the Macintosh SE to the Power Macintosh G3 could read, write and format IBM PC format 3½-inch disks, but few IBM-compatible computers had drives that did the reverse. 8-inch, 5¼-inch and 3½-inch drives were manufactured in a variety of sizes, most to fit standardized drive bays. Alongside the common disk sizes were non-classical sizes for specialized systems.
3,394	Floppy disks of the first standard are 8 inches in diameter, protected by a flexible plastic jacket. It was a read-only device used by IBM as a way of loading microcode. Read/write floppy disks and their drives became available in 1972, but it was IBM's 1973 introduction of the 3740 data entry system that began the establishment of floppy disks, called by IBM the Diskette 1, as an industry standard for information interchange. Formatted diskette for this system store 242,944 bytes. Early microcomputers used for engineering, business, or word processing often used one or more 8-inch disk drives for removable storage; the CP/M operating system was developed for microcomputers with 8-inch drives.
3,395	The family of 8-inch disks and drives increased over time and later versions could store up to 1.2 MB; many microcomputer applications did not need that much capacity on one disk, so a smaller size disk with lower-cost media and drives was feasible. The 5¼-inch drive succeeded the 8-inch size in many applications, and developed to about the same storage capacity as the original 8-inch size, using higher-density media and recording techniques.
3,396	The head gap of an 80‑track high-density 5¼‑inch drive is smaller than that of a 40‑track double-density drive but can also format, read and write 40‑track disks provided the controller supports double stepping or has a switch to do so. 5¼-inch 80-track drives were also called hyper drives. A blank 40‑track disk formatted and written on an 80‑track drive can be taken to its native drive without problems, and a disk formatted on a 40‑track drive can be used on an 80‑track drive. Disks written on a 40‑track drive and then updated on an 80 track drive become unreadable on any 40‑track drives due to track width incompatibility.
3,397	Single-sided disks were coated on both sides, despite the availability of more expensive double sided disks. The reason usually given for the higher price was that double sided disks were certified error-free on both sides of the media. Double-sided disks could be used in some drives for single-sided disks, as long as an index signal was not needed. This was done one side at a time, by turning them over ; more expensive dual-head drives which could read both sides without turning over were later produced, and eventually became used universally.
3,398	In the early 1980s, many manufacturers introduced smaller floppy drives and media in various formats. A consortium of 21 companies eventually settled on a 3½-inch design known as the Micro diskette, Micro disk, or Micro floppy, similar to a Sony design but improved to support both single-sided and double-sided media, with formatted capacities generally of 360 KB and 720 KB respectively. Single-sided drives of the consortium design first shipped in 1983, and double-sided in 1984. The double-sided, high-density 1.44 MB disk drive, which would become the most popular, first shipped in 1986. The first Macintosh computers used single-sided 3½-inch floppy disks, but with 400 KB formatted capacity. These were followed in 1986 by double-sided 800 KB floppies. The higher capacity was achieved at the same recording density by varying the disk-rotation speed with head position so that the linear speed of the disk was closer to constant. Later Macs could also read and write 1.44 MB HD disks in PC format with fixed rotation speed. Higher capacities were similarly achieved by Acorn's RISC OS and AmigaOS .
3,399	All 3½-inch disks have a rectangular hole in one corner which, if obstructed, write-enables the disk. A sliding detented piece can be moved to block or reveal the part of the rectangular hole that is sensed by the drive. The HD 1.44 MB disks have a second, unobstructed hole in the opposite corner that identifies them as being of that capacity.
3,400	In IBM-compatible PCs, the three densities of 3½-inch floppy disks are backwards-compatible; higher-density drives can read, write and format lower-density media. It is also possible to format a disk at a lower density than that for which it was intended, but only if the disk is first thoroughly demagnetized with a bulk eraser, as the high-density format is magnetically stronger and will prevent the disk from working in lower-density modes.

Subsets and Splits

No community queries yet

The top public SQL queries from the community will appear here once available.