1.
Illustration
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The origin of the word “illustration” is late Middle English, via Old French from Latin illustratio, from the verb illustrate. Contemporary illustration uses a range of styles and techniques, including drawing, painting, printmaking, collage, montage, digital design, multimedia. Most illustrators work on a freelance basis, depending on the purpose, illustration may be expressive, stylised, realistic or highly technical. This may include exploded views, cutaways, fly-throughs, reconstructions, instructional images, component designs, in contemporary illustration practice, 2D and 3D software is often used to create accurate representations that can be updated easily, and reused in a variety of contexts. In the art world, illustration has at times been considered of less importance than graphic design, original illustration art has been known to attract high prices at auction. The US artist Norman Rockwells painting Breaking Home Ties sold in a 2006 Sothebys auction for USD15.4 million, many other illustration genres are equally valued, with pinup artists such as Gil Elvgren and Alberto Vargas, for example, also attracting high prices. Historically, the art of illustration is closely linked to the processes of printing and publishing. The illustrations of medieval codices were known as illuminations, and were hand drawn. With the invention of the press during the 15th century, books became more widely distributed. Subjects included traditional folk tales, popular figures and every day life, hokusai’s The Great Wave of Kanazawa is a famous image of the time. During the 16th and 17th centuries in Europe, the main reproduction processes for illustration were engraving and etching, in 18th Century England, a notable illustrator was William Blake, who used relief etching. By the early 19th century, the introduction of lithography substantially improved reproduction quality, in Europe, notable figures of the early 19th Century were John Leech, George Cruikshank, Dickens illustrator Hablot Knight Browne, and, in France, Honoré Daumier. All contributed to both satirical and “serious” publications, at this time, there was a great demand for caricature drawings encapsulating social mores, types and classes. Although all fine art trained, their reputations were gained primarily as illustrators, in common with similar magazines such as the Parisian Le Voleur, Punch realised good illustration sold as well as good text. With publication continuing into the 21st Century, Punch chronicles a gradual shift in popular illustration, from the early 1800s newspapers, mass market magazines, and illustrated books had become the dominant consumer media in Europe and the New World. By the 19th Century, improvements in printing technology freed illustrators to experiment with color, in America, this led to a golden age of illustration from before the 1880s until the early 20th Century. A small group of illustrators became highly successful, with the imagery they created considered a portrait of American aspirations of the time
2.
Personal computer
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A personal computer is a multi-purpose electronic computer whose size, capabilities, and price make it feasible for individual use. PCs are intended to be operated directly by a end-user, rather than by an expert or technician. In the 2010s, PCs are typically connected to the Internet, allowing access to the World Wide Web, personal computers may be connected to a local area network, either by a cable or a wireless connection. In the 2010s, a PC may be, a multi-component desktop computer, designed for use in a location a laptop computer, designed for easy portability or a tablet computer. In the 2010s, PCs run using a system, such as Microsoft Windows, Linux. The very earliest microcomputers, equipped with a front panel, required hand-loading of a program to load programs from external storage. Before long, automatic booting from permanent read-only memory became universal, in the 2010s, users have access to a wide range of commercial software, free software and free and open-source software, which are provided in ready-to-run or ready-to-compile form. Since the early 1990s, Microsoft operating systems and Intel hardware have dominated much of the computer market, first with MS-DOS. Alternatives to Microsofts Windows operating systems occupy a minority share of the industry and these include Apples OS X and free open-source Unix-like operating systems such as Linux and Berkeley Software Distribution. Advanced Micro Devices provides the alternative to Intels processors. PC is an initialism for personal computer, some PCs, including the OLPC XOs, are equipped with x86 or x64 processors but not designed to run Microsoft Windows. PC is used in contrast with Mac, an Apple Macintosh computer and this sense of the word is used in the Get a Mac advertisement campaign that ran between 2006 and 2009, as well as its rival, Im a PC campaign, that appeared in 2008. Since Apples transition to Intel processors starting 2005, all Macintosh computers are now PCs, the “brain” may one day come down to our level and help with our income-tax and book-keeping calculations. But this is speculation and there is no sign of it so far, in the history of computing there were many examples of computers designed to be used by one person, as opposed to terminals connected to mainframe computers. Using the narrow definition of operated by one person, the first personal computer was the ENIAC which became operational in 1946 and it did not meet further definitions of affordable or easy to use. An example of an early single-user computer was the LGP-30, created in 1956 by Stan Frankel and used for science and it came with a retail price of $47, 000—equivalent to about $414,000 today. Introduced at the 1965 New York Worlds Fair, the Programma 101 was a programmable calculator described in advertisements as a desktop computer. It was manufactured by the Italian company Olivetti and invented by the Italian engineer Pier Giorgio Perotto, the Soviet MIR series of computers was developed from 1965 to 1969 in a group headed by Victor Glushkov
3.
Desk
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Desks often have one or more drawers, compartments, or pigeonholes to store items such as office supplies and papers. Desks are usually made of wood or metal, although materials such as tempered glass are sometimes seen, some desks have the form of a table, although usually only one side of a desk is suitable to sit at, unlike most usual tables. Some desks do not have the form of a table, for instance, a desk is a desk built within a large wardrobe-like cabinet. Since many people lean on a desk while using it, a desk must be sturdy, in most cases, people sit at a desk, either on a separate chair or a built-in chair. Some users stand at their desks using higher standing desks, the word desk originated from the Modern Latin word desca “table to write on”, from the mid 14th century. It is a modification of the Old Italian desco table, from Latin discus dish or disc, the word desk has been used figuratively since 1797. A desk may also be known as a bureau, counter, davenport, escritoire, lectern, reading stand, rolltop desk, school desk, workspace, or writing desk. Desk-style furniture appears not to have used in classical antiquity or in other ancient centers of literate civilization in the Middle East or Far East. Medieval illustrations show the first pieces of furniture which seem to have designed and constructed for reading and writing. Before the invention of the movable type printing press in the 15th century, the desks were designed with slots and hooks for bookmarks and for writing implements. Since manuscript volumes were sometimes large and heavy, desks of the period usually had massive structures, desks of the Renaissance and later eras had relatively slimmer structures, and more and more drawers were added as woodworking became more precise and cabinet-making became a distinct trade. It is often possible to find out if a table or other piece of furniture of those times was designed to be used as a desk, the basic desk forms were developed mostly in the 17th and 18th centuries. The modern ergonomic desk is a refinement of the mechanically complex drawing table or drafting table from the end of the 18th century and this allowed an increase in the number of the white-collar workers. As these office workers grew in number, desks were mass-produced for them in quantities, using newer. This was the first sharp division in desk manufacturing, thus, age alone does not guarantee that an antique desk is a masterpiece, since this split in quality took place more than a hundred years ago. More paper and correspondence drove the need for more complex desks and more specialized desks, such as the rolltop desk and it provided a relatively fast and cheap way to lock up the ever increasing flow of paperwork without having to file everything by the end of the day. Paper documents became voluminous enough to be stored separately in filing cabinets, the famous Wooton desk and others were the last manifestations of the pigeonhole style. The surfaces of some newer desks could be transformed into different shapes and angles, and were ideal for artists, draftsmen
4.
Computer case
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A computer case, also known as a computer chassis, tower, system unit, cabinet, base unit, or simply case, is the enclosure that contains most of the components of a computer. Cases are usually constructed from steel or aluminium, plastic is sometimes used, and other materials such as glass, wood and even Lego bricks have appeared in home-built cases. Cases can come in different sizes. The size and shape of a case is usually determined by the form factor of the motherboard. Consequently, personal computer form factors typically specify only the internal dimensions, Form factors for rack-mounted and blade servers may include precise external dimensions as well, since these cases must themselves fit in specific enclosures. For example, a designed for an ATX motherboard and power supply may take on several external forms such as a vertical tower. Full-size tower cases are larger in volume than desktop cases, with more room for drive bays. Desktop cases—and mini-tower cases under about 46 cm high—are popular in business environments where space is at a premium, currently, the most popular form factor for desktop computers is ATX, although microATX and small form factors have also become very popular for a variety of uses. In the high-end segment the unofficial and loosely defined XL-ATX specification appeared around 2009 and it extends the length of the mainboard to accommodate four graphics cards with dual-slot coolers. Some XL-ATX mainboards increase the width as well, to allow more space for the CPU, Memory PWM and, in some cases. While the market share of these exotic high-end mainboards is very low, almost all high-end cases, companies like In Win Development, Shuttle Inc. and AOpen originally popularized small cases, for which FlexATX was the most common motherboard size. As of 2010 Mini ITX has widely replaced FlexATX as the most common form factor mainboard standard. The latest mini ITX mainboards from Asus, Gigabyte, Zotac, high-end mini ITX mainboards support standard desktop CPUs, use standard memory DIMM sockets and feature a full size PCI-E 16× slot with support for the fastest graphics cards. This allows customers to build a fully fledged high-end computer in a smaller case. Apple Inc. has also produced the Mac Mini computer, which is similar in size to a standard CD-ROM drive, tower cases are often categorized as mini-tower, midi-tower, mid-tower or full-tower. The terms are subjective and inconsistently defined by different manufacturers, full tower cases are typically 56 cm or more in height and intended to stand on the floor. They have anywhere from six to ten externally accessible drive bays, the ratio of external to internal bays is shifting, however, as computing technology moves from floppy disks and CD-ROMs to large capacity hard drives, USB flash drives, and network-based solutions. The full tower case was developed to house file servers which would typically be tasked with serving data from expensive CD-ROM databases which held more data than the hard drives commonly available
5.
Power supply unit (computer)
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A power supply unit converts mains AC to low-voltage regulated DC power for the internal components of a computer. Modern personal computers universally use switched-mode power supplies, some power supplies have a manual switch for selecting input voltage, while others automatically adapt to the mains voltage. Most modern desktop computer power supplies conform to the ATX specification. While an ATX power supply is connected to the supply, it always provides a 5 Volt standby voltage so that the standby functions on the computer. ATX power supplies are turned on and off by a signal from the motherboard and they also provide a signal to the motherboard to indicate when the DC voltages are in spec, so that the computer is able to safely power up and boot. The most recent ATX PSU standard is version 2.31 of mid-2008, the desktop computer power supply changes alternating current from a wall socket to low-voltage direct current to operate the processor and peripheral devices. Several direct-current voltages are required, and they must be regulated with some accuracy to provide stable operation of the computer, a power supply rail or voltage rail refers to a single voltage provided by a power supply unit. Although the term is used in electronic engineering, many people, especially computer enthusiasts. First-generation microcomputer and home computer power supply units used a heavy step-down transformer, modern computers use switched-mode power supplies with a ferrite-cored high frequency transformer. The switched-mode supply is much lighter and less costly, and is more efficient, computer power supplies may have short circuit protection, overpower protection, overvoltage protection, undervoltage protection, overcurrent protection, and over temperature protection. Recent power supplies have a standby voltage available, to allow most of the system to be powered off. When the computer is powered down but the supply is still on, it can be started remotely via Wake-on-LAN. This standby voltage is generated by a power supply inside the unit. In older PSU designs, it was used to supply the voltage regulator, located on the side of the transformer. The regulator controls the switching transistors insulated by optocouplers or pulse transformers, for this reason, a detected shoutcut may cause to wait up to an hour, until it can successful power up again. This meantime is defined by the grid side located filter capacitors have been discharged by the installed bleeding resistors, Power supplies designed for worldwide use were equipped with an input voltage selector switch that allowed the user to configure the unit for use on local power grid. In the lower range, around 115 V, this switch is turned on changing the power grid voltage rectifier into a voltage doubler in delon circuit design. Connecting the unit configured for the range to a higher-voltage grid usually resulted in an immediate permanent damage
6.
Motherboard
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A motherboard is the main printed circuit board found in general purpose microcomputers and other expandable systems. It holds and allows communication between many of the electronic components of a system, such as the central processing unit and memory. In very old designs, copper wires were the discrete connections between card connector pins, but printed circuit boards soon became the standard practice, the Central Processing Unit, memory, and peripherals were housed on individual printed circuit boards, which were plugged into the backplate. The ubiquitous S-100 bus of the 1970s is an example of type of backplane system. During the late 1980s and 1990s, it became economical to move a number of peripheral functions onto the motherboard. Business PCs, workstations, and servers were more likely to need expansion cards, either for more robust functions, or for higher speeds, laptop and notebook computers that were developed in the 1990s integrated the most common peripherals. This even included motherboards with no upgradeable components, a trend that would continue as smaller systems were introduced after the turn of the century, memory, processors, network controllers, power source, and storage would be integrated into some systems. A motherboard provides the connections by which the other components of the system communicate. Unlike a backplane, it contains the central processing unit and hosts other subsystems. A typical desktop computer has its microprocessor, main memory, an important component of a motherboard is the microprocessors supporting chipset, which provides the supporting interfaces between the CPU and the various buses and external components. This chipset determines, to an extent, the features and capabilities of the motherboard, modern motherboards include, Sockets in which one or more microprocessors may be installed. In the case of CPUs in ball grid array packages, such as the VIA C3, as of 2007, some graphics cards require more power than the motherboard can provide, and thus dedicated connectors have been introduced to attach them directly to the power supply. Connectors for hard drives, typically SATA only, disk drives also connect to the power supply. Additionally, nearly all motherboards include logic and connectors to support commonly used devices, such as USB for mouse devices. Early personal computers such as the Apple II or IBM PC included only this minimal peripheral support on the motherboard, occasionally video interface hardware was also integrated into the motherboard, for example, on the Apple II and rarely on IBM-compatible computers such as the IBM PC Jr. Additional peripherals such as disk controllers and serial ports were provided as expansion cards, given the high thermal design power of high-speed computer CPUs and components, modern motherboards nearly always include heat sinks and mounting points for fans to dissipate excess heat. Motherboards are produced in a variety of sizes and shapes called computer form factor, however, the motherboards used in IBM-compatible systems are designed to fit various case sizes. As of 2007, most desktop computer motherboards use the ATX standard form factor — even those found in Macintosh and Sun computers, a cases motherboard and PSU form factor must all match, though some smaller form factor motherboards of the same family will fit larger cases
7.
Printed circuit board
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Components are generally soldered on the PCB. Advanced PCBs may contain components embedded in the substrate, PCBs can be single sided, double sided or multi-layer. Conductors on different layers are connected with vias, multi-layer PCBs allow for much higher component density. FR-4 glass epoxy is the primary insulating substrate, a basic building block of the PCB is an FR-4 panel with a thin layer of copper foil laminated to one or both sides. In multi-layer boards multiple layers of material are laminated together, printed circuit boards are used in all but the simplest electronic products. Alternatives to PCBs include wire wrap and point-to-point construction, PCBs require the additional design effort to lay out the circuit, but manufacturing and assembly can be automated. Manufacturing circuits with PCBs is cheaper and faster than other wiring methods as components are mounted and wired with one single part. A minimal PCB with a component used for easier prototyping is called a breakout board. When the board has no embedded components it is correctly called a printed wiring board or etched wiring board. However, the printed wiring board has fallen into disuse. A PCB populated with electronic components is called a printed circuit assembly, the IPC preferred term for assembled boards is circuit card assembly, and for assembled backplanes it is backplane assemblies. The term PCB is used both for bare and assembled boards. The world market for bare PCBs exceeded $60.2 billion in 2014, initially PCBs were designed manually by creating a photomask on a clear mylar sheet, usually at two or four times the true size. Starting from the diagram the component pin pads were laid out on the mylar. Rub-on dry transfers of common component footprints increased efficiency, traces were made with self-adhesive tape. Pre-printed non-reproducing grids on the mylar assisted in layout, to fabricate the board, the finished photomask was photolithographically reproduced onto a photoresist coating on the blank copper-clad boards. Modern PCBs are designed with dedicated software, generally in the following steps. Card dimensions and template are decided based on required circuitry and case of the PCB, the positions of the components and heat sinks are determined
8.
Microprocessor
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A microprocessor is a computer processor which incorporates the functions of a computers central processing unit on a single integrated circuit, or at most a few integrated circuits. Microprocessors contain both combinational logic and sequential digital logic, Microprocessors operate on numbers and symbols represented in the binary numeral system. The integration of a whole CPU onto a chip or on a few chips greatly reduced the cost of processing power. Integrated circuit processors are produced in numbers by highly automated processes resulting in a low per unit cost. Single-chip processors increase reliability as there are many electrical connections to fail. As microprocessor designs get better, the cost of manufacturing a chip generally stays the same, before microprocessors, small computers had been built using racks of circuit boards with many medium- and small-scale integrated circuits. Microprocessors combined this into one or a few large-scale ICs, the internal arrangement of a microprocessor varies depending on the age of the design and the intended purposes of the microprocessor. Advancing technology makes more complex and powerful chips feasible to manufacture, a minimal hypothetical microprocessor might only include an arithmetic logic unit and a control logic section. The ALU performs operations such as addition, subtraction, and operations such as AND or OR, each operation of the ALU sets one or more flags in a status register, which indicate the results of the last operation. The control logic retrieves instruction codes from memory and initiates the sequence of operations required for the ALU to carry out the instruction, a single operation code might affect many individual data paths, registers, and other elements of the processor. As integrated circuit technology advanced, it was feasible to manufacture more and more complex processors on a single chip, the size of data objects became larger, allowing more transistors on a chip allowed word sizes to increase from 4- and 8-bit words up to todays 64-bit words. Additional features were added to the architecture, more on-chip registers sped up programs. Floating-point arithmetic, for example, was not available on 8-bit microprocessors. Integration of the point unit first as a separate integrated circuit and then as part of the same microprocessor chip. Occasionally, physical limitations of integrated circuits made such practices as a bit slice approach necessary, instead of processing all of a long word on one integrated circuit, multiple circuits in parallel processed subsets of each data word. With the ability to put large numbers of transistors on one chip and this CPU cache has the advantage of faster access than off-chip memory, and increases the processing speed of the system for many applications. Processor clock frequency has increased more rapidly than external memory speed, except in the recent past, a microprocessor is a general purpose system. Several specialized processing devices have followed from the technology, A digital signal processor is specialized for signal processing, graphics processing units are processors designed primarily for realtime rendering of 3D images
9.
Central processing unit
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The computer industry has used the term central processing unit at least since the early 1960s. The form, design and implementation of CPUs have changed over the course of their history, most modern CPUs are microprocessors, meaning they are contained on a single integrated circuit chip. An IC that contains a CPU may also contain memory, peripheral interfaces, some computers employ a multi-core processor, which is a single chip containing two or more CPUs called cores, in that context, one can speak of such single chips as sockets. Array processors or vector processors have multiple processors that operate in parallel, there also exists the concept of virtual CPUs which are an abstraction of dynamical aggregated computational resources. Early computers such as the ENIAC had to be rewired to perform different tasks. Since the term CPU is generally defined as a device for software execution, the idea of a stored-program computer was already present in the design of J. Presper Eckert and John William Mauchlys ENIAC, but was initially omitted so that it could be finished sooner. On June 30,1945, before ENIAC was made, mathematician John von Neumann distributed the paper entitled First Draft of a Report on the EDVAC and it was the outline of a stored-program computer that would eventually be completed in August 1949. EDVAC was designed to perform a number of instructions of various types. Significantly, the programs written for EDVAC were to be stored in high-speed computer memory rather than specified by the wiring of the computer. This overcame a severe limitation of ENIAC, which was the considerable time, with von Neumanns design, the program that EDVAC ran could be changed simply by changing the contents of the memory. Early CPUs were custom designs used as part of a larger, however, this method of designing custom CPUs for a particular application has largely given way to the development of multi-purpose processors produced in large quantities. This standardization began in the era of discrete transistor mainframes and minicomputers and has accelerated with the popularization of the integrated circuit. The IC has allowed increasingly complex CPUs to be designed and manufactured to tolerances on the order of nanometers, both the miniaturization and standardization of CPUs have increased the presence of digital devices in modern life far beyond the limited application of dedicated computing machines. Modern microprocessors appear in electronic devices ranging from automobiles to cellphones, the so-called Harvard architecture of the Harvard Mark I, which was completed before EDVAC, also utilized a stored-program design using punched paper tape rather than electronic memory. Relays and vacuum tubes were used as switching elements, a useful computer requires thousands or tens of thousands of switching devices. The overall speed of a system is dependent on the speed of the switches, tube computers like EDVAC tended to average eight hours between failures, whereas relay computers like the Harvard Mark I failed very rarely. In the end, tube-based CPUs became dominant because the significant speed advantages afforded generally outweighed the reliability problems, most of these early synchronous CPUs ran at low clock rates compared to modern microelectronic designs. Clock signal frequencies ranging from 100 kHz to 4 MHz were very common at this time, the design complexity of CPUs increased as various technologies facilitated building smaller and more reliable electronic devices
10.
Disk storage
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Disk storage is a general category of storage mechanisms where data are recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is a device implementing such a storage mechanism, notable types are the hard disk drive containing a non-removable disk, the floppy disk drive and its removable floppy disk, and various optical disc drives and associated optical disc media. Audio information was recorded by analog methods. Similarly the first video disc used a recording method. In the music industry, analog recording has mostly replaced by digital optical technology where the data are recorded in a digital format with optical information. The first commercial digital disk storage device was the IBM350 which shipped in 1956 as a part of the IBM305 RAMAC computing system, the random-access, low-density storage of disks was developed to complement the already used sequential-access, high-density storage provided by tape drives using magnetic tape. Disk storage is now used in computer storage and consumer electronic storage, e. g. audio CDs and video discs. Digital disk drives are block storage devices, each disk is divided into logical blocks. Blocks are addressed using their logical block addresses, read from or writing to disk happens at the granularity of blocks. Originally the disk capacity was low and has been improved in one of several ways. Improvements in mechanical design and manufacture allowed smaller and more precise heads, advancements in data compression methods permitted more information to be stored in each of the individual sectors. The drive stores data onto cylinders, heads, and sectors, the sectors unit is the smallest size of data to be stored in a hard disk drive and each file will have many sectors units assigned to it. The smallest entity in a CD is called a frame, which consists of 33 bytes, the other nine bytes consist of eight CIRC error-correction bytes and one subcode byte used for control and display. The information is sent from the processor to the BIOS into a chip controlling the data transfer. This is then sent out to the drive via a multi-wire connector. Once the data are received onto the board of the drive. The data are passed to a chip on the circuit board that controls the access to the drive. The drive is divided into sectors of data stored onto one of the sides of one of the internal disks, an HDD with two disks internally will typically store data on all four surfaces
11.
Hard disk drive
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The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a manner, meaning that individual blocks of data can be stored or retrieved in any order. HDDs are a type of storage, retaining stored data even when powered off. Introduced by IBM in 1956, HDDs became the dominant secondary storage device for computers by the early 1960s. Continuously improved, HDDs have maintained this position into the era of servers. More than 200 companies have produced HDDs historically, though after extensive industry consolidation most current units are manufactured by Seagate, Toshiba, as of 2016, HDD production is growing, although unit shipments and sales revenues are declining. While SSDs have higher cost per bit, SSDs are replacing HDDs where speed, power consumption, small size, the primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixes corresponding to powers of 1000, the two most common form factors for modern HDDs are 3. 5-inch, for desktop computers, and 2. 5-inch, primarily for laptops. HDDs are connected to systems by standard interface cables such as PATA, SATA, Hard disk drives were introduced in 1956, as data storage for an IBM real-time transaction processing computer and were developed for use with general-purpose mainframe and minicomputers. The first IBM drive, the 350 RAMAC in 1956, was approximately the size of two medium-sized refrigerators and stored five million six-bit characters on a stack of 50 disks. In 1962 the IBM350 RAMAC disk storage unit was superseded by the IBM1301 disk storage unit, cylinder-mode read/write operations were supported, and the heads flew about 250 micro-inches above the platter surface. Motion of the head array depended upon a binary system of hydraulic actuators which assured repeatable positioning. The 1301 cabinet was about the size of three home refrigerators placed side by side, storing the equivalent of about 21 million eight-bit bytes, access time was about a quarter of a second. Also in 1962, IBM introduced the model 1311 disk drive, users could buy additional packs and interchange them as needed, much like reels of magnetic tape. Later models of removable pack drives, from IBM and others, became the norm in most computer installations, non-removable HDDs were called fixed disk drives. Some high-performance HDDs were manufactured with one head per track so that no time was lost physically moving the heads to a track, known as fixed-head or head-per-track disk drives they were very expensive and are no longer in production. In 1973, IBM introduced a new type of HDD code-named Winchester and its primary distinguishing feature was that the disk heads were not withdrawn completely from the stack of disk platters when the drive was powered down. Instead, the heads were allowed to land on an area of the disk surface upon spin-down
12.
Optical disc drive
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Some drives can only read from certain discs, but recent drives can both read and record, also called burners or writers. Compact discs, DVDs, and Blu-ray discs are common types of media which can be read. Optical disc drives that are no longer in production include CD-ROM drive, CD writer drive, combo drive, as of 2015, DVD writer drive supporting all existing recordable and rewritable DVD formats is the most common for desktop PCs and laptops. There are also the DVD-ROM drive, BD-ROM drive, Blu-ray Disc combo drive and they are also very commonly used in computers to read software and consumer media distributed on disc, and to record discs for archival and data exchange purposes. Floppy disk drives, with capacity of 1, USB flash drives, high-capacity, small, and inexpensive, are suitable where read/write capability is required. Large backups are often made on external hard drives, as their price has dropped to a level making this viable. 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 format created by Sony. The CD-ROM format was developed by Sony and Denon, introduced in 1984, as an extension of Compact Disc Digital Audio, the CD-ROM has a storage capacity of 650 MB. Also in 1984, Sony introduced a LaserDisc data storage format, in 1987, Sony demonstrated the erasable and rewritable 5. 25-inch optical drive. The first Blu-Ray prototype was unveiled by Sony in October 2000, 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, initially, CD-type lasers with a wavelength of 780 nm were used. For DVDs, the wavelength was reduced to 650 nm, two main servomechanisms are used, the first to maintain the proper distance between lens and disc, to ensure the laser beam is focused as a small laser spot on the disc. The second servo moves the head along the discs radius, keeping the beam on the track. Optical disk media are read beginning at the radius to the outer edge. This is detected by photodiodes that create corresponding electrical signals, an optical disk recorder encodes data onto a recordable CD-R, DVD-R, DVD+R, or BD-R disc by selectively heating parts of an organic dye layer with a laser. This changes the reflectivity of the dye, thereby creating marks that can be read like the pits, for recordable discs, the process is permanent and the media can be written to only once
