Glasses

Scraping, fracturing, or breakage of the lenses require time-consuming and costly professional repair, though modern plastic lenses are almost indestructible and very scratch-resistant. Fibre channel (FC) interfaces are left to discussions of server drives. The lenses themselves can also become greasy or trap vapour when eating hot food or swimming or walking in rain, reducing visibility significantly. However, as of 2005, performance of SATA and PATA disks is comparable. Even though the late-20th century saw the creation of light frames, such as those made of titanium, very flexible frames, and new lens materials and optical coatings, glasses can still cause problems during rigorous sports. In order for EIDE's performance to increase (while keeping the cost of the associated electronics low), it was realized that the only way to do this was to move from "parallel" interfaces to "serial" interfaces, the result of which is the SATA interface. Another unpopular aspect of glasses is their inconvenience. The increase in SCSI performance came at a price — its interfaces were more expensive.

Some people who find that wearing glasses may look nerdy turn to contact lenses instead, especially under peer pressure. While EIDE was introduced, though, SCSI manufacturers continued to improve SCSI's performance. This conception probably comes from an era when most people were illiterate and the first people to wear glasses were those who did a lot of reading. These drives were known as EIDE. An example of halo effect is seen in the stereotype that those who wear glasses are intelligent or, especially in teen culture, even geeks and nerds. IDE manufacturers attempted to close this speed gap by introducing Logical Block Addressing (LBA). In popular culture, glasses were all the disguise Superman and Wonder Woman needed to hide in plain view as alter egos Clark Kent and Diana Prince, respectively. IDE drives were slower because they did not have as big a cache as the SCSI drives, and they could not write directly to RAM.

And of course John Lennon wore his round "granny glasses" from some of his time with the Beatles to his assassination in 1980. Eventually, IDE manufacturers wanted the speed of IDE to approach the speed of SCSI drives. Masaharu Morimoto wears glasses to separate his professional persona as a chef from his stage persona as Iron Chef Japanese. This advance was known as "Integrated Drive Electronics" or IDE. British comedic actor Eric Sykes, who became profoundly deaf as an adult, wears glasses that contain no lenses, but are in fact a bone-conducting hearing aid. When the price of electronics dropped (and because of a demand by consumers) the electronics that had been stored on the controller card was moved to the disk drive itself. Drew Carey continued to wear glasses for the same reason after getting corrective laser eye surgery. SCSI (originally named SASI for Shugart (sic) Associates) or Small Computer System Interface was an early competitor with ESDI.

British soap star Anne Kirkbride had the same problem: her character on Coronation Street, Deirdre Barlow, became so well-known for her big frames that she was expected to wear them at social gatherings and in international tours, even though Kirkbride has always worn contact lenses. It allowed for faster communication between the PC and the disk. American Senator Barry Goldwater continued to wear lensless horn-rimmed spectacles after being fitted with contact lenses because he was not recognizable without his trademark glasses. ESDI was an interface developed by Maxtor. For some celebrities, glasses form part of their identity. Most RLL drives also needed to be "compatible" with the controllers that communicated with them. Glasses can be a major part of personal expression, from the extravagance of Elton John and Dame Edna Everage, from Groucho Marx to John Denver to Lisa Loeb all the way to the varied professional personas of eyeglass-wearing knowledge workers. RLL (Run Length Limited) was a way of encoding bits onto the platters that allowed for better density.

On the other hand, many people are attracted to people who wear glasses, and glasses are available in a wide range of styles, materials, and even designer labels. MFM drives required that the electronics on the "controller" be compatible with the electronics on the drive — disks and controllers had to be compatible. Contact lenses also provide much improved peripheral vision. As far as PC history is concerned, the major drive families have been MFM, RLL, ESDI, SCSI, IDE and EIDE, and now SATA. Glasses are often regarded as unattractive, and many people prefer to wear contact lenses for that reason. As of early 2005, the "smallest" desktop hard disk in production has a capacity of 40 gigabytes, while the largest-capacity internal drives are a half terabyte (500 gigabytes), with external drives at or exceeding one terabyte. Many people have several pairs of glasses, one for each task or distance, with specific glasses for reading, computer use, and television watching. In the latter half of the 1990s, hard drives with capacities of 1 gigabyte and greater became available.

Others have lenses specifically intended for use with computer monitors at a fixed distance. With early personal computers, a drive with a 20 megabyte capacity was considered large. Some modern multifocal lenses give a smooth transition between these lenses, unnoticeable by most wearers. The capacity of hard drives has grown exponentially over time. These were originally separate lenses, as invented by Benjamin Franklin. The appearance in the late 1990s of high-speed external interfaces such as USB and FireWire has made external disk systems popular among regular users once again, especially for users who move large amounts of data between two or more locations, and most hard disk makers now make their disks available in external cases. Traditional multifocal lenses have two or three distinct viewing areas, each requiring a conscious effort of refocusing. External SCSI drives were also popular with older microcomputers such as the Apple II series and the Commodore 64, and were also used extensively in servers, a usage which is still popular today.

As people age, their ability to focus is lessened and many decide to use multiple-focus lenses, bifocal or even trifocal to cover all the situations in which they use their sight. Every Mac made between 1986 and 1998 has a SCSI port on the back, making external expansion easy; also, "toaster" Macs did not have easily accessible hard drive bays (or, in the case of the Mac Plus, any hard drive bay at all), so on those models, external SCSI disks were the only reasonable option. Lenses can be ground to specific eyes, but in most cases standard off-the-shelf prescriptions suffice, but require custom-fitting to particular frames. While internal drives became the system of choice on PCs, external hard drives remained popular for much longer on the Apple Macintosh and other platforms. Magnifying lenses for reading that are used to treat mild hypermetropia and presbyopia can be bought off the shelf, but most glasses are made to a particular prescription, based on degree of myopia or hypermetropia combined with astigmatism. Hard disk makers started marketing to end users as well as OEMs, and by the mid-1990s, hard disks had become available on retail store shelves. Glasses can be very simple. The IBM PC/XT had an internal hard disk, however, and this started a trend toward buying "bare" drives (often by mail order) and installing them directly into a system.

None of these conditions is considered a disease. Most microcomputer hard disk drives in the early 1980s were not sold under their manufacturer's names, but by OEMs as part of larger peripherals (such as the Corvus Disk System and the Apple ProFile). As most people age the crystalline lens of the eye loses elasticity resulting in presbyopia, which limits their ability to focus on nearby objects. In fact, in its factory configuration the original IBM PC (IBM 5150) was not equipped with a hard drive. Some would say "the rays of light converge at an imaginary point behind the retina." Astigmatism is a condition in which parallel rays of light entering the eye converge at two separate locations, either before and/or after the retina. Because of this, hard disks were not commonly used with microcomputers until after 1980, when Seagate Technology introduced the ST-506, the first 5.25-inch hard drive, with a capacity of 5 megabytes. Hyperopia is a condition in which parallel rays of light entering the eye do not converge prior to reaching the retina. Before the early 1980s, most hard disks had 8-inch (20 cm) or 14-inch (35 cm) platters, required an equipment rack or a large amount of floor space (especially the large removable-media drives, which were often referred to as "washing machines"), and in many cases needed high-amperage or even three-phase power hookups due to the large motors they used.

Myopia is a condition in which parallel rays of light entering the eye converge before reaching to retina. For many years, hard disks were large, cumbersome devices, more suited to use in the protected environment of a data center or large office than in a harsh industrial environment (due to their delicacy), or small office or home (due to their size and power consumption). Emmetropia, the condition of ideal focus is described as two parallel rays of light entering the eye and converging on or at the retina. Project head designer/lead designer Kenneth Haughton named it after the Winchester 30-30 rifle after the developers called it the "30-30" because of its two 30 MB spindles. Glasses fitted with corrective lenses are a common means of correcting focus problems such as myopia (nearsightedness, short-sightedness) and hyperopia (farsightedness, long-sightedness). Almost all modern disk drives now use this technology, and the term "Winchester" became a common description for all hard disks, though generally falling out of use during the 1990s. Virtual reality glasses and helmets have separate video screens for each eye and a method for determining the direction the head is turned. In 1973, IBM introduced the 3340 "Winchester" disk system the first to use a sealed head/disk assembly (HDA).

One kind of electronic 3D spectacles uses electronic shutters. The first disk drive to use removable media was the IBM 1311 drive, which used the IBM 1316 disk pack to store two million characters. Another kind of 3D glasses uses polarized filters. The IBM 1301 Disk Storage Unit, announced in 1961, introduced the usage of a separate head for each data surface. 3D glasses made of cardboard and plastic are distributed at 3D movies. A single head was used for access to all the platters, making the average access time very slow. The classic 3D glasses have one red lens and one blue lens. This drive had fifty 24 inch platters, with a total capacity of five million characters.

Classic 3D glasses create the illusion of three dimensions when viewing specially prepared images. The first hard disk drive was the IBM 350 Disk File, invented by Reynold Johnson and introduced in 1955 with the IBM 305 computer. The illusion of three dimensions on a two dimensional surface can be created by providing each eye with different visual information. In 2005 the first cellular telephones to include hard disk drives were introduced by Samsung and Nokia. Polarized sunglasses may present some difficulties for pilots in that reflections from water and other structures often used to gauge altitude may be removed, or instrument readings on liquid crystal displays may be blocked. Applications for hard disk drives expanded to include personal video recorders, digital audio players, digital organizers and digital cameras. Popular among fishermen and hunters, polarized sunglasses allow wearers to see into water when normally glare or reflected light would be seen. Hard disks are also found in network attached storage (NAS) devices, but for large volumes of data are most efficiently used in a storage area network (SAN).

Polarization filters remove horizontal rays of light, which can cause glare. From the original use of a hard drive in a single computer, techniques for guarding against hard disk failure were developed such as the redundant array of independent disks (RAID). Light polarization is an added feature that can be applied to sunglass lenses. However, for large (several GiB) filesystems, this data rarely occupies more than several MiB, and therefore cannot possibly account for the apparent "loss" of tens of GBs. Still, they offer the convenience of not having to carry both clear glasses and sunglasses to those who frequently go indoors and outdoors during the course of a day. Another side point is that many people mistakenly attribute the discrepancy in reported and advertised capacities to reserved space used for file system and partition accounting information. Unfortunately, many car windshields protect the passengers from UV light, while not shielding from bright visible light, making photochromic lenses ineffective where they are most needed. KiB, MiB, GiB) since their definitions are unambiguous.

Glasses with photosensitive lenses, called photochromic lenses, become darker in the presence of UV light. For this very reason, many utilities that report capacity have begun to use the aforementioned IEC standard binary prefixes (e.g. Sunglasses vary greatly and many offer more style than protection. Since utilities provided by the operating system probably define a gigabyte as 2³⁰, or 1073741824, bytes, the reported capacity of the drive will be closer to 186.26 GB (actually, GiB), a difference of well over 7 percent. It is possible to have lenses that look very dark and yet offer little ultraviolet protection. This uses the proper SI definition of "giga," 10⁹ and can be considered as an approximation of a gibibyte. Due to changes in the atmosphere, ultraviolet levels are much higher than in the past and ultraviolet protection for eyes and skin is even more important. For example, a drive advertised as 200 GB can be expected to store close to 200 x 10⁹, or 200 billion, bytes.

Good sunglasses should also protect against ultraviolet light. This trend became habit and continued to be applied to the prefixes "mega," "giga," and even "tera." Obviously the discrepancy becomes much more noticeable in reported capacities in the multiple gigabyte range, and users will often notice that the volume capacity reported by their OS is significantly less than that advertised by the hard drive manufacturer. plano) lenses that are darkened to provide protection against bright visible light. The IEC only standardized binary prefixes in 1999, so 2¹⁰ (1024) bytes was called a kilobyte because 1024 is "close enough" to the metric prefix kilo, which is defined as 10³ or 1000. Sunglasses may be made with either prescription or non-prescription (i.e. This is largely for historical reasons, since when storage capacities started to exceed thousands of bytes, there were no standard binary prefixes. Main article: Sunglasses. Hard drive manufacturers often use the metric definition of the prefixes "giga" and "mega", whilst nearly all operating system utilities report capacities using binary definitions for the prefixes.

Corrective glasses with plastic lenses can often be used in the place of safety glasses in many environments; this is one advantage that they have over contact lenses. In the United Kingdom, Cumana, a manufacturer of disk drives for Acorn computers, ceased manufacturing drives in 1995. The pictured wraparound safety glasses are evidence of this style change with the close fitting nature of the wraparound dispensing with the need for side shields. There have also been a number of notable mergers in the hard disk industry:. Recent safety glasses have tended to be given a more stylish design, in order to encourage their use. Rodime was also an important manufacturer during the 1980s, but stopped making drives in the early 1990s amid the shakeout and now concentrates on technology licensing; they hold a number of patents related to 3.5-inch form factor hard drives. They may provide less eye protection than goggles, face shields or other forms of eye protection, but their light weight increases the likelihood that they will actually be used. Many other smaller companies (like Kalok, Microscience, LaPine, Areal, Priam and PrairieTek) also did not survive the shakeout, and had disappeared by 1993; Micropolis was able to hold on until 1997, and JTS, a relative latecomer to the scene, lasted only a few years and was gone by 1999.

Some safety glasses are designed to fit over corrective glasses or sunglasses. Another notable failure was MiniScribe, who went bankrupt in 1990 after it was found that they had "cooked the books" and inflated sales numbers for several years. The lenses of safety glasses can also be shaped for correction. The first notable casualty of the business in the PC era was Computer Memories International or CMI; after the 1985 incident with the faulty 20MB AT drives, CMI's reputation never recovered, and they exited the hard drive business in 1987. For example, those used in medicine may be expected to protect against blood splatter while safety glasses in a factory might have stronger lenses and a stronger frame with additional shields at the temples. Dozens of former hard drive manufacturers have gone out of business, merged, or closed their hard drive divisions; as capacities and demand for products increased, profits became hard to find, and there were shakeouts in the late 1980s and late 1990s. Safety glasses can vary in the level of protection they provide. Toshiba is a major manufacturer of 2.5-inch and 1.8-inch notebook drives.

Although safety lenses may be constructed from a variety of materials that vary in impact resistance, certain standards suggest that they maintain a minimum 1mm thickness at the thinest point regardless of material. Fujitsu continues to make specialist notebook and SCSI drives but exited the mass market in 2001. Safety glasses are usually made with shatter-resistant plastic lenses to protect the eye from flying debris. Most of the world's hard disks are now manufactured by just a handful of large firms: Seagate, Maxtor (now owned by Seagate), Western Digital, Samsung, and Hitachi, the former drive manufacturing division of IBM. Lenses made to conform to the prescription of an ophthalmologist or optometrist are called prescription lenses and are used to make prescription glasses. See also: hard disk drive partitioning, master boot record, file system, drive letter assignment, boot sector. Glasses correcting for myopia will have negative diopter strengths. ATA drives larger than 8 GiB are always accessed by LBA, due to the 8 GiB limit described above.

Over-the-counter reading glasses are typically rated at +1.00 to +3.00 diopters. To maintain some degree of compatibility with older computers, LBA mode generally has to be requested explicitly by the host computer. The power of a lens is generally measured in diopters. ATA drives can either use their native CHS parameters (only on very early drives; hard drives made since the early 1990s use zone bit recording, and thus don't have a set number of sectors per track), use a "translated" CHS profile (similar to what SCSI host adapters provide), or run in ATA LBA mode, as specified by ATA-2. Corrective lenses modify the focal length of the eye to alleviate the effects of shortsightedness (myopia), longsightedness (hyperopia) or astigmatism. Because PCs use CHS addressing internally, the BIOS code on PC SCSI host adapters does CHS-to-LBA translation, and provides a set of CHS drive parameters that tries to match the total number of LBA blocks as closely as possible. Either of these designs offers dramatically better ability to withstand the stresses of daily wear and the occasional accident. SCSI mode page commands can be used to get the physical specifications of the disk, but this is not used to read or write data; this is an artifact of the early days of SCSI, circa 1986, when a disk attached to a SCSI bus could just as well be an ST-506 or ESDI drive attached through a bridge (and therefore having a CHS configuration that was subject to change) as it could be a native SCSI device.

Other frames have spring-loaded hinges. SCSI drives, however, have always used LBA addressing, which describes the disk as a linear, sequentially-numbered set of blocks. For instance, it is now possible to purchase frames made of special memory metal alloys that return to their correct shape after being bent. The 8.4 and 128 GiB limits are soft limits: the PC simply ignores the extra capacity and reports a drive of the maximum size it is able to communicate with. Despite the increasing popularity of contact lenses and laser corrective eye surgery, glasses remain very common and their technology has not stood still. The 2.1, 4.2 and 32 GiB limits are hard limits: fitting a drive larger than the limit results in a PC that refuses to boot, unless the drive includes special jumpers to make it appear as a smaller capacity. These designs were not immediately successful, however, and various styles with attached handles such as scissors glasses and lorgnettes remained fashionable throughout the 18th and into the early 19th century. Even after the introduction of LBA, similar limitations reappeared several times over the following years: at 2.1, 4.2, 8.4, 32, and 128 GiB.

The modern style of glasses, held by temples passing over the ears, was developed in 1727 by the British optician Edward Scarlett. When drives larger than 504 MiB began to appear in the mid-1990s, many system BIOSes had problems communicating with them, requiring LBA BIOS upgrades or special driver software to work correctly. Girolamo Savonarola suggested that eyepieces could be held in place by a ribbon passed over the wearer's head, this in turn secured by the weight of a hat. The origin of the CHS limit lies in a combination of the limitations of IBM's BIOS interface (which allowed 1024 cylinders, 256 heads and 64 sectors; sectors were counted from 1, reducing that number to 63, giving an addressing limit of 8064 MiB or 7.8 GiB), and a hardware limitation of the AT's hard disk controller (which allowed up to 65536 cylinders and 256 sectors, but only 16 heads, putting its addressing limit at 2^28 bits or 128 GiB). Early eyepieces were designed to be either held in place by hand or by exerting pressure on the nose (pince-nez). The traditional CHS limit was 1024 cylinders, 16 heads and 63 sectors; on a drive with 512-byte sectors, this comes to 504 MiB (528 megabytes). Over time, the construction of spectacle frames also evolved. CHS describes the disk space in terms of its physical dimensions, data-wise; this is the traditional way of accessing a disk on IBM PC compatible hardware, and while it works well for floppies (for which it was originally designed) and small hard disks, it caused problems when disks started to exceed the design limits of the PC's CHS implementation.

The first lenses for correcting astigmatism were constructed by the British astronomer George Airy in 1827. The more recent mode is the LBA (Logical Block Addressing), used by SCSI drives and newer ATA drives (ATA drives power up in CHS mode for historical reasons). The American scientist Benjamin Franklin, who suffered from both myopia and presbyopia, invented bifocals in 1784 to avoid having to regularly switch between two pairs of glasses. The older mode is CHS addressing (Cylinder-Head-Sector), used on old ST-506 and ATA drives and internally by the PC BIOS. However, it was not until 1604 that Johannes Kepler published in his treatise on optics and astronomy, the first correct explanation as to why convex and concave lenses could correct presbyopia and myopia. Addressing modes There are two modes of addressing the data blocks on more recent hard disks. Nicholas of Cusa is believed to have discovered the benefits of concave lens in the treatment of myopia (nearsightedness). Most FireWire/IEEE 1394 models are able to daisy-chain in order to continue adding peripherals without requiring additional ports on the computer itself.

These early spectacles had convex lenses that could correct the farsightedness (presbyopia) that commonly develops as a symptom of aging. FireWire/IEEE 1394 and USB(1.0/2.0) hard disks are external units containing generally ATA or SCSI drives with ports on the back allowing very simple and effective expansion and mobility. Bacon's published writings describe the magnifying glass (which he did not invent), but make no mention of glasses. Serial ATA does away with master/slave setups entirely, placing each drive on its own channel (with its own set of I/O ports) instead. Other stories, possibly legendary, credit Roger Bacon with the invention. This was mostly remedied by the mid-1990s, when ATA's specfication was standardised and the details began to be cleaned up, but still causes problems occasionally (especially with CD-ROM and DVD-ROM drives, and when mixing Ultra DMA and non-UDMA devices). In 1738, a Florentine historian named Domenico Manni reported that a tombstone in Florence credited one Salvino d'Armato (died 1317) with the invention of glasses. ATA drives have typically had no problems with interleave or data rate, due to their controller design, but many early models were incompatible with each other and couldn't run in a master/slave setup (two drives on the same cable).

Based on this evidence, Redi credited another Dominican monk, Fra Alessandro da Spina of Pisa, with the re-invention of glasses after their original inventor kept them a secret, a claim contained in da Spina's obituary record. The SCSI bus speed had no bearing on the drive's internal speed because of buffering between the SCSI bus and the drive's internal data bus; however, many early drives had very small buffers, and thus had to be reformatted to a different interleave (just like ST-506 drives) when used on slow computers, such as early IBM PC compatibles and Apple Macintoshes. In 1676, Franciscus Redi, a professor of medicine at the University of Pisa, wrote that he possessed a 1289 manuscript whose author complains that he would be unable to read or write were it not for the recent invention of glasses, and a record of a sermon given in 1305, in which the speaker, a Dominican monk named Fra Giordano da Rivalto, remarked that glasses had been invented less than twenty years previously, and that he had met the inventor. SCSI originally had just one speed, 5 MHz (for a maximum data rate of 5 megabytes per second), but later this was increased dramatically. The identity of the original inventor is unknown, although a possible source is the Arabs, who may have had magnifying lenses in the 10th century. ESDI drives typically also had jumpers to set the number of sectors per track and (in some cases) sector size. Glasses were possibly invented in northern Italy, most likely in the late 1280s. a 15 or 20 megabit drive wouldn't run on a 10 megabit controller).

. ESDI also supported multiple data rates (ESDI drives always used 2,7 RLL, but at 10, 15 or 20 megabits per second), but this was usually negotiated automatically by the drive and controller; most of the time, however, 15 or 20 megabit ESDI drives weren't downward compatible (i.e. Sunglasses protect against high levels of visible and ultraviolet light. (An RLL-certified drive could run on a MFM controller, but with 1/3 less data capacity and speed.). Safety glasses are a kind of eye protection against flying debris or visible and near visible light or radiation. In some cases, the drive was overengineered just enough to allow the MFM-certified model to run at the faster data rate; however, this was often unreliable and was not recommended. Corrective spectacles have lenses shaped to correct vision abnormalities, such as myopia. Many ST-506 interface drives were only certified by the manufacturer to run at the lower MFM data rate, while other models (usually more expensive versions of the same basic drive) were certified to run at the higher RLL data rate.

Hydrophobic coatings designed to ease cleaning are also available, as are anti-reflective coatings intended to improve night vision and make the wearer's eyes more visible. Later on, controllers using 2,7 RLL (or just "RLL") encoding increased this by half, to 7.5 megabits per second; it also increased drive capacity by half. Scratch-resistant coatings can be applied to most plastic lenses giving them similar scratch resistance to glass. The first ST-506 disks used Modified Frequency Modulation (MFM) encoding (which is still used on the common "1.44 MB" (1.4 MiB) 3.5-inch floppy), and ran at a data rate of 5 megabits per second. Some plastics have a greater index of refraction than most types of glass, allowing thinner lenses for a given prescription. Back in the days of the ST-506 interface, the data encoding scheme was also important. Some plastics also have more advantageous optical properties than glass, such as better transmission of visible light and greater absorption of ultraviolet light. A hard disk is generally accessed over one of a number of bus types, including ATA (IDE, EIDE), Serial ATA, SCSI, SAS, FireWire (aka IEEE 1394), USB, and Fibre Channel.

Glasses were originally made from glass, but many are now made from plastic (often polycarbonate or CR-39) due to the danger of breakage and the greater weight of glass lenses. Most spin at only 4,200 rpm or 5,400 rpm, though the newest top models spin at 7,200 rpm. In hipster slang they are cheaters. Notebook hard drives, which are physically smaller than their desktop counterparts, tend to be slower and have less capacity. Spectacles is often shortened to specs. The fastest workstation and server hard drives spin at 15,000 rpm, and can achieve sequential media transfer speeds of up to 100 MB/s. Glasses are more often called eyeglasses in North American English, occasionally spectacles in British English, and (rarely) frames or lenses. In 2005, a typical workstation hard disk might store between 80 GB and 500 GB of data, rotate at 7,200 to 10,000 rpm, and have a sequential media transfer rate of over 50 MB/s.

Historical types include the pince nez, monocle, and lorgnette. Consequently, hard disks can store much more data than floppy disk, and access and transmit it faster. Modern glasses are typically supported by pads on the bridge of the nose and by temples placed over the ears. Using rigid platters and sealing the unit allows much tighter tolerances than in a floppy disk. Special glasses are used for viewing three-dimensional images or experiencing virtual reality. This means that no failures attributed to the head-disk interface were seen before at least 50,000 start-stop cycles during testing. Glasses, spectacles, or eyeglasses are frames bearing lenses worn in front of the human eyes, sometimes for purely aesthetic reasons but normally for vision correction or eye protection. For example, the Maxtor DiamondMax series of desktop hard drives are rated to 50,000 start-stop cycles.

Eyeglasses were a common part of the hipster persona, for example Dizzy Gillespie. However, the decay rate is not linear — when a drive is younger and has fewer start/stop cycles, it has a better chance of surviving the next startup than an older, higher-mileage drive (as the head literally drags along the drive's surface until the air bearing is established). Cheaters is used in the hipster argot. Most manufacturers design the sliders to survive 50,000 contact cycles before the chance of damage on startup rises above 50%. Lenses is also sometimes used to refer to framed eyepieces, although it is not common. The sliders (the part of the heads that are closest to the disk and contain the pickup coil itself) are designed to reliably survive a number of landings and takeoffs from the disk surface, though wear and tear on these microscopic components eventually takes its toll. Frames is sometimes used to refer to framed eyepieces, although it is not common. While the disk is spinning, the heads are supported by an air bearing and experience no physical contact wear.

In contrast, glass eye refers to a cosmetic prosthetic artificial eye that replaces a missing eye. Spring tension from the head mounting constantly pushes the heads towards the disk. Eye glasses or eyeglasses is a word used in North American English. When a sudden, sharp movement is detected by the built-in motion sensor in the PowerBook, internal hard disk heads automatically unload themselves into the parking zone to reduce the risk of any potential data loss or scratches made. Also in frequent use is the shortened form, specs. Apple Computer has created a technology for their new PowerBook line of laptop computers called Sudden Motion Sensor, or SMS. Spectacles is widely used in Britain and occasionally in the US, in addition to use by professional opticians. Other manufacturers also use this technology.

Compare with other meanings of the word glass. IBM pioneered drives with "head unloading" technology that lifts the heads off the platters onto "ramps" instead of having them rest on the platters, reducing the risk of stiction. Pair of glasses (or just glasses) is commonly used in Britain and in North America. Newer drives are designed such that the rotational inertia in the platters is used to safely park the heads in the case of unexpected power loss. However, especially in old models, sudden power interruptions or a power supply failure can result in the drive shutting down with the heads in the data zone, which increases the risk of data loss. Normally, when powering down, a hard disk moves its heads to a safe area of the disk, where no data is ever kept (the landing zone).

Head crashes can be caused by electronic failure, a sudden power failure, physical shock, wear and tear, or poorly manufactured disks. For Giant Magnetoresistive (GMR) heads in particular, a minor head crash from contamination (that does not remove the magnetic surface of the disk) will still result in the head temporarily overheating, due to friction with the disk surface, and renders the disk unreadable until the head temperature stabilizes. Due to the extremely close spacing of the heads and disk surface, any contamination of the read-write heads or disk platters can lead to a head crash — a failure of the disk in which the head scrapes across the platter surface, often grinding away the thin magnetic film. This air passes through an internal filter to remove any leftover contaminants from manufacture, any particles that may have somehow entered the drive, and any particles generated by head crash.

The air inside the operating drive is constantly moving too, being swept in motion by friction with the spinning disk platters. You can see these breather holes on all drives -- they usually have a warning sticker next to them, informing the user not to cover the holes. Very high humidity year-round will cause accelerated wear of the drive's heads (by increasing stiction, or the tendency for the heads to stick to the disk surface, which causes physical damage to the disk and spindle motor). The filter also allows moisture in the air to enter the drive.

They have a permeable filter (a breather filter) between the top cover and inside of the drive, to allow the pressure inside and outside the drive to equalize while keeping out dust and dirt. Hard disk drives are not airtight. This does not apply to pressurized enclosures, like an airplane cabin.) Modern drives include temperature sensors and adjust their operation to the operating environment. (Specially manufactured sealed and pressurized drives are needed for reliable high-altitude operation, above about 10,000 feet.

If the air pressure is too low, the air will not exert enough force on the flying head, the head will not be at the proper height, and there is a risk of head crashes and data loss. A hard disk drive requires a certain range of air pressures in order to operate properly. Another common misconception is that a hard drive is totally sealed. Instead, the system relies on air pressure inside the drive to support the heads at their proper flying height while the disk is in motion.

Contrary to popular belief a hard disk drive does not contain a vacuum. given the submicroscopic gap between the heads and disk. The disk surface and the drive's internal environment must therefore be kept immaculately clean to prevent damage from fingerprints, hair, dust, smoke particles, etc. The hard disk's read-write heads fly on an air bearing (a cushion of air) only nanometres above the disk surface.

The (mostly) sealed enclosure protects the drive internals from dust, condensation, and other sources of contamination. technology, by which impending failures can often be predicted, allowing the user to be alerted in time to prevent data loss. Also, most major hard drive and motherboard vendors now support S.M.A.R.T. Modern drive firmware is capable of scheduling reads and writes efficiently on the disk surfaces and remapping sectors of the disk which have failed.

The associated electronics control the movement of the read-write armature and the rotation of the disk, and perform reads and writes on demand from the disk controller. The armature moves the heads radially across the platters as they spin, allowing each head access to the entirety of the platter. Moving along and between the platters on a common armature are read-write heads, with one head for each platter surface. A typical hard disk drive design consists of a central axis or spindle upon which the platters spin at a constant rotational velocity.

The information can be read by a read-write head which senses electrical change as the magnetic fields pass by in close proximity as the platter rotates. Information is written to the disk by transmitting an electromagnetic flux through an antenna or read-write head that is very close to a magnetic material, which in turn changes its polarization due to the flux. Each platter has a planar magnetic surface on which digital data may be stored. A hard disk uses rigid rotating platters (disks).

. A hard disk drive (HDD, or also hard drive) is a non-volatile data storage device that stores data on a magnetic surface layered onto hard disk platters. 2005 - Introduction of faster SAS (Serial Attached SCSI). 2005 - Serial ATA 3G standardized.

2005 - 500 GB hard drive. 2003 - Serial ATA introduced. 2002 - 137 GB addressing space barrier broken. 1998 - UltraDMA/33 and ATAPI standardized.

1997 - 10 gigabyte hard drive (CS). 1995 - 2 gigabyte hard drive (CS). 1994 - ATA-1 standardized. 1991 - 100 megabyte hard drive (CS).

1986 - Standardization of SCSI. 1980 - first 5.25-inch Winchester drive, the Shugart ST-506, 5 megabyte (CS). 1956 - first commercial hard disk, the IBM 350 RAMAC disk drive, 5 megabyte. (CS) denotes an improvement in the consumer market.

In December 2005, however, Maxtor itself was acquired by Seagate for USD1.9 billion. Quantum bought DEC's storage division in 1994, and later (2000) sold the hard disk division to Maxtor to concentrate on tape drives. In 2003, following the controversy over the mass failures of its Deskstar 75GXP range, hard disk pioneer IBM sold the majority of its disk division to Hitachi, who renamed it Hitachi Global Storage Technologies. JTS infamously merged with Atari in 1996, giving it the capital it needed to bring its drive range into production.

In 1995, Conner Peripherals announced a merger with Seagate (who had earlier bought Imprimis from CDC), which was completed in early 1996. Tandon sold its disk manufacturing division to Western Digital (which was then a controller maker and ASIC house) in 1988; by the early 1990s Western Digital disks were among the top sellers. Random access time: from 5 ms to 15 ms. Outer Zone: from 74.0 MB/sec to 111.4 MB/sec.

Inner Zone: from 44.2 MB/sec to 74.5 MB/sec. Transfer Rate