Why a Laptop?

Why a Laptop?

               The main advantage of a laptop computer versus a desktop computer is its mobility as well as its reduced size. On the other hand, the prce is generally higher for slightly less impressive performance and the laptop's hardware configuration is much less adaptable, even though it is possible to connect additional external peripherals thanks to its numerous I/O ports. Therefore, the motivation for buying a laptop computer must above all be a need for mobility or a need to save space.

                 Moreover, with the emergence of wireless networks, and WiFi in particular, it is becoming very easy to connect to the Internet in public Hot-Spots or simply in any room of your home as long as it is equipped with a WiFi terminal.

               For advanced multimedia uses (e.g. digital video manipulation connecting a digital camera or an mp3 player, etc.), the choice should fall on both the computer's performance (both graphic as well as computing power) and on the types and number of I/O ports that are available.

latest laptops

latest laptop

Types of Scanners

Types of Scanners

Drum Scanner

Drum Scanner

            Drum scanners capture image information mostly with photomultiplier tubes (PMT), rather than the charge-coupled device (CCD) arrays found in flatbed scanners and inexpensive film scanners. "Reflective and transmissive originals are mounted on an acrylic cylinder, the scanner drum, which rotates at high speed while it passes the object being scanned in front of precision optics that deliver image information to the PMTs. Most modern color drum scanners use three matched PMTs, which read red, blue, and green light, respectively. Light from the original artwork is split into separate red, blue, and green beams in the optical bench of the scanner."[3] Photomultipliers offer superior dynamic range and for this reason drum scanners using photomultiplier tubes can extract more detail from very dark shadow areas of a transparency than flatbed scanners using CCD sensors. The smaller dynamic range of the CCD sensors, versus photomultiplier tubes, can lead to loss of shadow detail, especially when scanning very dense transparency film. Some DeskTop Publishing drum scanners use cheaper illumination/sensor systems than PMT such as halogen lamps and photodiodes, which have their dynamic range less than that of photomultipliers but higher than that of charge coupled devices.

            The drum scanner gets its name from the clear acrylic cylinder, the drum, on which the original artwork is mounted for scanning. Depending on size, it is possible to mount originals up to 20"x28", but maximum size varies by manufacturer. "One of the unique features of drum scanners is the ability to control sample area and aperture size independently. The sample size is the area that the scanner encoder reads to create an individual pixel. The aperture is the actual opening that allows light into the optical bench of the scanner. The ability to control aperture and sample size separately is particularly useful for smoothing film grain when scanning black-and-white and color negative originals."

            While drum scanners are capable of scanning both reflective and transmissive artwork, a good-quality flatbed scanner can produce good scans from reflective artwork. As a result, drum scanners are rarely used to scan prints now that high-quality, inexpensive flatbed scanners are readily available. Film, however, is where drum scanners continue to be the tool of choice for high-end applications. Because film can be wet-mounted to the scanner drum and because of the exceptional sensitivity of the PMTs, drum scanners are capable of capturing very subtle details in film originals.

Drum Scaner

             The situation as of 2014 was that only a few companies continued to manufacture drum scanners. While prices of both new and used units dropped from the start of the 21st century, they were still much more costly than CCD flatbed and film scanners. Image quality produced by flatbed scanners had improved to the degree that the best ones were suitable for most graphic-arts operations, and they replaced drum scanners in many cases as they were less expensive and faster. However, drum scanners with their superior resolution (up to 24,000 PPI), color gradation, and value structure continued to be used for scanning images to be much enlarged, and for museum-quality archiving of photographs and print production of high-quality books and magazine advertisements. As second-hand drum scanners became more plentiful and less costly, many fine-art photographers acquired them.

Flatbed

             

This type of scanner is sometimes called reflective scanner because it works by shining white light onto the object to be scanned and reading the intensity and color of light that is reflected from it, usually a line at a time. They are designed for scanning prints or other flat, opaque materials but some have available transparency adapters, which for a number of reasons, in most cases, are not very well suited to scanning film.

Flatbed Scanner

CCD scanner

            "A flatbed scanner is usually composed of a glass pane (or platen), under which there is a bright light (often xenon, LED or cold cathode fluorescent) which illuminates the pane, and a moving optical array in CCD scanning. CCD-type scanners typically contain three rows (arrays) of sensors with red, green, and blue filters."

CCD Scanner

CIS scanner

              Contact image sensor (CIS) scanning consists of a moving set of red, green and blue LEDs strobed for illumination and a connected monochromatic photodiode array under a rod lens array for light collection. "Images to be scanned are placed face down on the glass, an opaque cover is lowered over it to exclude ambient light, and the sensor array and light source move across the pane, reading the entire area. An image is therefore visible to the detector only because of the light it reflects. Transparent images do not work in this way, and require special accessories that illuminate them from the upper side. Many scanners offer this as an option."

CIS scanner

Film

Film scanner

            This type of scanner is sometimes called a slide or transparency scanner and it works by passing a narrowly focused beam of light through the film and reading the intensity and color of the light that emerges. "Usually, uncut film strips of up to six frames, or four mounted slides, are inserted in a carrier, which is moved by a stepper motor across a lens and CCD sensor inside the scanner. Some models are mainly used for same-size scans. Film scanners vary a great deal in price and quality." The lowest-cost dedicated film scanners can be had for less than $50 and they might be sufficient for modest needs. From there they inch up in staggered levels of quality and advanced features upward of five figures. "The specifics vary by brand and model and the end results are greatly determined by the level of sophistication of the scanner's optical system and, equally important, the sophistication of the scanning software."

Roller scanner

              Scanners are available that pull a flat sheet over the scanning element between rotating rollers. They can only handle single sheets up to a specified width (typically about 210 mm, the width of many printed letters and documents), but can be very compact, just requiring a pair of narrow rollers between which the document is passed. Some are portable, powered by batteries and with their own storage, eventually transferring stored scans to a computer over a USB or other interface.

Roller scanner

3D scanner

3D scanners collect data on the three-dimensional shape and appearance of an object.

3D scanner

Planetary scanner

Hand

Hand scanners are moved over the subject to be imaged by hand. There are two different types: document and 3D scanners.

Hand document scanner

              "Hand held document scanners are manual devices that are dragged across the surface of the image to be scanned by hand. Scanning documents in this manner requires a steady hand, as an uneven scanning rate produces distorted images; an indicator light on the scanner indicates if motion is too fast. They typically have a "start" button, which is held by the user for the duration of the scan; some switches to set the optical resolution; and a roller, which generates a clock pulse for synchronization with the computer. Older hand scanners were monochrome, and produced light from an array of green LEDs to illuminate the image";[8] later ones scan in monochrome or color, as desired. A hand scanner may have a small window through which the document being scanned could be viewed. In the early 1990s many hand scanners had a proprietary interface module specific to a particular type of computer, such as an Atari ST or Commodore Amiga. Since the introduction of the USB standard, it is the interface most commonly used. As hand scanners are much narrower than most normal document or book sizes, software (or the end user) needed to combine several narrow "strips" of scanned document to produce the finished article.

Inexpensive portable battery-powered "glide-over" hand scanners, typically capable of scanning an area as wide as a normal letter and much longer, remain, available as of 2014.

Hand 3D scanner

               Handheld 3D scanners are used in industrial design, reverse engineering, inspection and analysis, digital manufacturing and medical applications. "To compensate for the uneven motion of the human hand, most 3D scanning systems rely on the placement of reference markers, typically adhesive reflective tabs that the scanner uses to align elements and mark positions in space."

Portable

              Image scanners are usually used in conjunction with a computer which controls the scanner and stores scans. Small portable scanners, either roller-fed or "glide-over" hand-operated, operated by batteries and with storage capability, are available for use away from a computer; stored scans can be transferred later. Many can scan both small documents such as business cards and till receipts, and letter-sized documents.

portable

Smartphone scanner apps

            The higher-resolution cameras fitted to some smartphones can produce reasonable quality document scans by taking a photograph with the phone's camera and post-processing it with a scanning app, a range of which are available for most phone operating systems, to whiten the background of a page, correct perspective distortion so that the shape of a rectangular document is corrected, convert to black-and-white, etc. Many such apps can scan multiple-page documents with successive camera exposures and output them either as a single file or multiple page files. Some smartphone scanning apps can save documents directly to online storage locations, such as Dropbox and Evernote, send via email or fax documents via email-to-fax gateways.

Smartphone scanner apps

             Smartphone scanner apps can be broadly divided into three categories: 1) document scanning apps primarily designed to handle documents and output PDF, and sometimes JPEG, files, 2) photo scanning apps that output JPEG files, and have editing functions useful for photo rather than document editing; and 3) barcode-like QR code scanning apps that then search the internet for information associated with the code.

History of Scanners

History of Scanners

Pantelegraph

            Modern scanners are considered the successors of early telephotography and fax input devices.

           The pantelegraph (Italian: pantelegrafo; French: pantélégraphe) was an early form of facsimile machine transmitting over normal telegraph lines developed by Giovanni Caselli, used commercially in the 1860s, that was the first such device to enter practical service. It used electromagnets to drive and synchronize movement of pendulums at the source and the distant location, to scan and reproduce images. It could transmit handwriting, signatures, or drawings within an area of up to 150 x 100mm.

            Édouard Belin's Belinograph of 1913, scanned using a photocell and transmitted over ordinary phone lines, formed the basis for the AT&T Wirephoto service. In Europe, services similar to a wirephoto were called a Belino. It was used by news agencies from the 1920s to the mid-1990s, and consisted of a rotating drum with a single photodetector at a standard

Caselli's pantelegraph machanism

speed of 60 or 120 rpm (later models up to 240 rpm). They send a linear analog AM signal through standard telephone voice lines to receptors, which synchronously print the proportional intensity on special paper. Color photos were sent as three separated RGB filtered images consecutively, but only for special events due to transmission costs.

Belinograph BEP2V wirephoto machine by Edouard Belin 1930

Scanner

Scanner

            A scanner is a device that images a printed page or graphic by digitizing it, producing an image made of tiny pixels of different brightness and color values which are represented numerically and sent to the computer. Scanners scan graphics, but they can also scan pages of text which are then run through OCR (Optical Character Recognition) software that identifies the individual letter shapes and creates a text file of the page's contents.

Scanner

            In computing, an image scanner often abbreviated to just scanner, although the term is ambiguous out of context (bar code scanner, CAT scanner, etc.)is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. Commonly used in offices are variations of the desktop flatbed scanner where the document is placed on a glass window for scanning. Hand-held scanners, where the device is moved by hand, have evolved from text scanning "wands" to 3D scanners used for industrial design, reverse engineering, test and measurement, orthotics, gaming and other applications. Mechanically driven scanners that move the document are typically used for large-format documents, where a flatbed design would be impractical.

            Modern scanners typically use a charge-coupled device (CCD) or a contact image sensor (CIS) as the image sensor, whereas drum scanners, developed earlier and still used for the highest possible image quality, use a photomultiplier tube (PMT) as the image sensor. A rotary scanner, used for high-speed document scanning, is a type of drum scanner that uses a CCD array instead of a photomultiplier. Non-contact planetary scanners essentially photograph delicate books and documents. All these scanners produce two-dimensional images of subjects that are usually flat, but sometimes solid; 3D scanners produce information on the three-dimensional structure of solid objects.

            Digital cameras can be used for the same purposes as dedicated scanners. When compared to a true scanner, a camera image is subject to a degree of distortion, reflections, shadows, low contrast, and blur due to camera shake (reduced in cameras with image stabilization). Resolution is sufficient for less demanding applications. Digital cameras offer advantages of speed, portability and non-contact digitizing of thick documents without damaging the book spine. As of 2010 scanning technologies were combining 3D scanners with digital cameras to create full-color, photo-realistic 3D models of objects.

           In the biomedical research area, detection devices for DNA microarrays are called scanners as well. These scanners are high-resolution systems (up to 1 µm/ pixel), similar to microscopes. The detection is done via CCD or a photomultiplier tube.

Keyboard safety

Keyboard safety

       If dirt, food, or liquid gets under its keycaps, a keyboard can develop all sorts of problems, including keys that stutter, get stuck, or just stop working. The very best maintenance tip for a keyboaryd is to keep fod and beverages away from it completely. After the monitor, the keyboard should be cleaned more frequently than any other component on the PC. The keyboard is an open-faced device that collects whatever falls or spills on it. To clean a keyboard and perform preventive maintenance, use the following steps:

• The easiest and best way to clean a keyboard is to turn it upside-down and shake it.

• You can open a cleaning hole so that large items can fall out by removing the keycaps of the last three keys on the right-hand end of the keyboard, which are the -,+, and ENTER keys of the Numeric keypad. To remove a keycap, gently pry it up with a small flat-bladed screwdriver.

• Use a can of compressed air to blow out the keyboard. Use the air stream to sweep the debris toward the removed keys or toward one end of the keyboard.

• Use a non static blower brush,vrush vacuum, or a probe to lightly loosen any large or stubborn debris and then stake the keyboard or use compressed air to blow it out.

• If one or two keys are sticking or have stopped working, disconnect the keyboard from the PC and pry off the keycap (the part with the letter or number printed on it) with a screwdriver or another thin flat-bladed tool. Clean under and around the key switch using a cotton swab with a small amount of isopropyl alcohol on it. Use compressed air to blow it dry and replace the key(s).

• Anytime liquid spills on a keyboard, immediately disconnect it from the PC (it gets its power from the pC cable) and turn it upside down. Besides this shut down your computer immediately. The popular practice is simply to let the liquid dry. The problem with this practice is that most liquids contain minerals and materials that are acidic to metals. You keyboard will never be the same unless the offending liquid is removed before it dries.

• If the keyboard has had soda pop, fruit juice, or some other sticky liquid spilled into it and the keys are beginning to stick and stutter, your choices are to replace the keyboard or wash it. Understand that introducing water into an electronic deviceis always risky, but if you use proper care, you can wash a keyboard. Newer keyboards are sealed under the key switches to protect the keyboard grid. Anything that spills in the keyboard is likely to settle on the keyboard membrance as sticky gunk. Use warm, clean water to rinse the residue out of the keyboard.

• After you have cleaned the keyboard, replace any keycaps you removed or replace the keyboard's cover.

• Most of the time, you also need to clean the outsides of the keys and keyboard case. Alcohol works the best because it evaporates without leaving moisture behind to seep inside the keyboard. Never pour the alcohol directly on the keys or case. Pour a small amount on the cloth and then wipe the keys and case. The same goes for the cleaner, if you choose to use one. A cotton swab dipped in cleaner or alcohol will get tight spots. Agin, be absolutely sure that the keyboard is dry berore connecting it to the PC and powering it up.

• After you've cleaned the keyboard and are absolutely sure that the keyboard is dry, reconnect it to the PC and reboot the system. Watch the POST process carefully for keyboard errors. After the PC is running, test the keyboard by pressing each key and verifying its action.

Laser Printer

Laser Printer

           The barrier to the laser printer to this point has been cost-not only the cost of the printer itself, but the cost of its supplies. The laser printer was born out of the technology used in the copy machine. Tn fact, its original concepts were developed at the Xerox Palo Alto Research Center (PARC), where a laser was added to Xerox copier technology to create a printer.

laser Printer

          Laser printing is an electrostatic digital printing process. It produces high-quality text and graphics (and moderate-quality photographs) by repeatedly passing a laser beam back and forth over a negatively charged cylindrical drum to define a differentially-charged image. The drum then selectively collects electrically charged powdered ink (toner), and transfers the image to paper, which is then heated in order to permanently fuse the text and/or imagery. As with digital photocopiers and multi function/all-in-one inkjet printers, laser printers employ a xerographic printing process. However, laser printing differs from analog photocopiers in that the image is produced by the direct scanning of the medium across the printer's photoreceptor. This enables laser printing to copy images more quickly than most photocopiers.

          Invented at Xerox PARC in the 1970s, laser printers were introduced for the office and then home markets in subsequent years by IBM, Canon, Xerox, Apple, Hewlett-Packard and many others. Over the decades, quality and speed have increased as price has fallen, and the once cutting-edge printing devices are now ubiquitous.

Contents   
1 History
2 Printing process
2.1 Raster image processing
2.2 Charging
2.3 Exposing
2.4 Developing
2.5 Transferring
2.6 Fusing
2.7 Cleaning
2.8 Multiple steps occurring at once
3 Performance
4 Color laser printers
4.1 Comparison with inkjet printers
4.2 Anti-counterfeiting marks
5 Smart chips in toner cartridges
6 Safety hazards, health risks, and precautions
6.1 Toner clean-up
6.2 Ozone hazards
6.3 Respiratory health risks
6.4 Air transport ban
7 See also
8 References
9 External links

History


           In the 1960s, the Xerox Corporation held a dominant position in the photocopier market. In 1969, Gary Starkweather, who worked in Xerox's product development department, had the idea of using a laser beam to 'draw' an image of what was to be copied directly onto the copier drum. After transferring to the recently formed Palo Alto Research Center (Xerox PARC) in 1971, Starkweather adapted a Xerox 7000 copier to create SLOT (Scanned Laser Output Terminal). In 1972, Starkweather worked with Butler Lampson and Ronald Rider to add a control system and character generator, resulting in a printer called EARS (Ethernet, Alto Research character generator, Scanned laser output terminal) -- which later became the Xerox 9700 laser printer.

            The first commercial implementation of a laser printer was the IBM 3800 in 1976. It was designed for data centers, where it replaced line printers attached to mainframe computers. The IBM 3800 was used for high-volume printing on continuous stationery, and achieved speeds of 215 pages per minute (ppm), at a resolution of 240 dots per inch (dpi). Over 8,000 of these printers were sold. The Xerox 9700 was brought to market in 1977. Unlike the IBM 3800, the Xerox 9700 was not targeted to replace any particular existing printers; but, it did have limited support for the loading of fonts. The Xerox 9700 excelled at printing high-value documents on cut-sheet paper with varying content (e.g., insurance policies).

             In 1979, inspired by the Xerox 9700's commercial success, Japanese camera and optics company, Canon, developed a low-cost, desktop laser printer: the Canon LBP-10. Canon then began work on a much-improved print engine, the Canon CX, resulting in the LBP-CX printer. Lacking experience in selling to computer users, Canon sought partnerships with three Silicon Valley companies: Diablo Data Systems (who turned them down), Hewlett-Packard (HP), and Apple Computer.

           The first laser printer designed for office use reached market in 1981: the Xerox Star 8010. The system used a desktop metaphor that was unsurpassed in commercial sales, until the Apple Macintosh. Although it was innovative, the Star workstation was a prohibitively expensive (US$17,000) system, affordable only to a fraction of the businesses and institutions at which it was targeted.

            The first laser printer intended for mass-market sales was the HP LaserJet, released in 1984; it used the Canon CX engine, controlled by HP software. The LaserJet was quickly followed by printers from Brother Industries, IBM, and others. First-generation machines had large photosensitive drums, of circumference greater than the loaded paper's length. Once faster-recovery coatings were developed, the drums could touch the paper multiple times in a pass, and therefore be smaller in diameter.

           In 1985, Apple introduced the LaserWriter (also based on the Canon CX engine), but used the newly released PostScript page-description language. Up until this point, each manufacturer used its own page-description language, making the supporting software complex and expensive. PostScript allowed the use of text, fonts, graphics, images, and color largely independent of the printer's brand or resolution. PageMaker, written by Aldus for the Macintosh and LaserWriter, was also released in 1985 and the combination became very popular for desktop publishing.:13/23:364 Laser printers brought exceptionally fast and high-quality text printing, with multiple fonts on a page, to the business and consumer markets. No other commonly-available printer during this era could also offer this combination of features.

Printing process

           A laser beam (typically, an aluminium gallium arsenide (AlGaAs) semiconductor laser) projects an image of the page to be printed onto an electrically-charged, selenium-coated, rotating, cylindrical drum (or, more commonly in subsequent versions, organic photoconductors). Photo conductivity allows the charged electrons to fall away from the areas exposed to light. Powdered ink (toner) particles are then electrostatically attracted to the charged areas of the drum that have not been laser-beamed. The drum then transfers the image onto paper (which is passed through the machine) by direct contact. Finally the paper is passed onto a finisher, which uses intense heat to instantly fuse the toner/image onto the paper.

There are typically seven steps involved in the process:

Raster image processing
              The document to be printed is encoded in a page description language such as PostScript, Printer Command Language (PCL), or Open XML Paper Specification (OpenXPS). The raster image processor converts the page description into a bitmap which is stored in the printer's raster memory. Each horizontal strip of dots across the page is known as a raster line or scan line.

             Laser printing differs from other printing technologies in that each page is always rendered in a single continuous process without any pausing in the middle, while other technologies like inkjet can pause every few lines. To avoid a buffer underrun (where the laser reaches a point on the page before it has the dots to draw there), a laser printer typically needs enough raster memory to hold the bitmap image of an entire page.

            Memory requirements increase with the square of the dots per inch, so 600 dpi requires a minimum of 4 megabytes for monochrome, and 16 megabytes for color at 600 dpi. For fully graphical output using a page description language, a minimum of 1 megabyte of memory is needed to store an entire monochrome letter/A4 sized page of dots at 300 dpi. At 300 dpi, there are 90,000 dots per square inch (300 dots per linear inch). A typical 8.5 × 11 sheet of paper has 0.25-inch (6.4 mm) margins, reducing the printable area to 8.0 by 10.5 inches (200 mm × 270 mm), or 84 square inches. 84 sq/in × 90,000 dots per sq/in = 7,560,000 dots. 1 megabyte = 1,048,576 bytes, or 8,388,608 bits, which is just large enough to hold the entire page at 300 dpi, leaving about 100 kilobytes to spare for use by the raster image processor.

           In a color printer, each of the four CMYK toner layers is stored as a separate bitmap, and all four layers are typically preprocessed before printing begins, so a minimum of 4 megabytes is needed for a full-color letter-size page at 300 dpi.

           During the 1980s, memory chips were still very expensive, which is why entry-level laser printers in that era always came with four-digit suggested retail prices in U.S. dollars. Memory prices later plunged, and 1200 dpi printers have been widely available in the consumer market since 2008. 2400 dpi electrophotographic printing plate makers, essentially laser printers that print on plastic sheets, are also available.

Charging

            In older printers, a corona wire positioned parallel to the drum, or in more recent printers, a primary charge roller, projects an electrostatic charge onto the photoreceptor (otherwise named the photo conductor unit), a revolving photosensitive drum or belt, which is capable of holding an electrostatic charge on its surface while it is in the dark.

            An AC bias is applied to the primary charge roller to remove any residual charges left by previous images. The roller will also apply a DC bias on the drum surface to ensure a uniform negative potential.

          Numerous patents[specify] describe the photosensitive drum coating as a silicon sandwich with a photocharging layer, a charge leakage barrier layer, as well as a surface layer. One version[specify] uses amorphous silicon containing hydrogen as the light receiving layer, Boron nitride as a charge leakage barrier layer, as well as a surface layer of doped silicon, notably silicon with oxygen or nitrogen which at sufficient concentration resembles machining silicon nitride.

Exposing

Exposing

        The laser is aimed at a rotating polygonal mirror, which directs the laser beam through a system of lenses and mirrors onto the photoreceptor. The cylinder continues to rotate during the sweep and the angle of sweep compensates for this motion. The stream of rasterized data held in memory turns the laser on and off to form the dots on the cylinder. Lasers are used because they generate a narrow beam over great distances. The laser beam neutralizes (or reverses) the charge on the black parts of the image, leaving a static electric negative image on the photoreceptor surface to lift the toner
particles.

         Some non-laser printers (LED printers) expose by an array of light emitting diodes spanning the width of the page, rather than by a laser ("exposing" is also known as "writing" in some documentation).

Developing
         
           The surface with the latent image is exposed to toner, fine particles of dry plastic powder mixed with carbon black or coloring agents. The toner particles are given a negative charge, and are electrostatically attracted to the photoreceptor's latent image, the areas touched by the laser. Because like charges repel, the negatively charged toner will not touch the drum where the negative charge remains.

Transferring

          The photoreceptor is pressed or rolled over paper, transferring the image. Higher-end machines use a positively charged transfer roller on the back side of the paper to pull the toner from the photoreceptor to the paper.

Fusing

          The paper passes through rollers in the fuser assembly where heat of up to 200 °C (392 °F) and pressure bonds the plastic powder to the paper.

          One roller is usually a hollow tube (heat roller) and the other is a rubber backed roller (pressure roller). A radiant heat lamp is suspended in the centre of the hollow tube, and its inferred energy uniformly heats the roller from the inside. For proper bonding of the toner, the fuser roller must be uniformly hot.

         Some printers use a very thin flexible metal fuser roller, so there is less mass to be heated and the fuser can more quickly reach operating temperature. If paper moves through the fuser more slowly, there is more roller contact time for the toner to melt, and the fuser can operate at a lower temperature. Smaller, inexpensive laser printers typically print slowly, due to this energy-saving design, compared to large high speed printers where paper moves more rapidly through a high-temperature fuser with a very short contact time.

Cleaning

            When the print is complete, an electrically neutral soft plastic blade cleans any excess toner from the photoreceptor and deposits it into a waste reservoir, and a discharge lamp removes the remaining charge from the photoreceptor.

           Toner may occasionally be left on the photoreceptor when unexpected events such as a paper jam occur. The toner is on the photoconductor ready to apply, but the operation failed before it could be applied. The toner must be wiped off and the process restarted.

Multiple steps occurring at once

           Once the raster image generation is complete all steps of the printing process can occur one after the other in rapid succession. This permits the use of a very small and compact unit, where the photoreceptor is charged, rotates a few degrees and is scanned, rotates a few more degrees and is developed, and so forth. The entire process can be completed before the drum completes one revolution.

            Different printers implement these steps in distinct ways. LED printers actually use a linear array of light-emitting diodes to "write" the light on the drum. The toner is based on either wax or plastic, so that when the paper passes through the fuser assembly, the particles of toner melt. The paper may or may not be oppositely charged. The fuser can be an infrared oven, a heated pressure roller, or (on some very fast, expensive printers) a xenon flash lamp. The warmup process that a laser printer goes through when power is initially applied to the printer consists mainly of heating the fuser element.

Performance

           As with most electronic devices, the cost of laser printers has fallen markedly over the years. In 1984, the HP LaserJet sold for $3500, had trouble with even small, low resolution graphics, and weighed 32 kg (71 lb). As of 2008, low-end monochrome laser printers often sell for less than $75. These printers tend to lack onboard processing and rely on the host computer to generate a raster image, but outperform the 1984 LaserJet in nearly all situations.

          Laser printer speed can vary widely, and depends on many factors, including the graphic intensity of the job being processed. The fastest models can print over 200 monochrome pages per minute (12,000 pages per hour). The fastest color laser printers can print over 100 pages per minute (6000 pages per hour). Very high-speed laser printers are used for mass mailings of personalized documents, such as credit card or utility bills, and are competing with lithography in some commercial applications.

           The cost of this technology depends on a combination of factors, including the cost of paper, toner, drum replacement, as well as the replacement of other items such as the fuser assembly and transfer assembly. Often printers with soft plastic drums can have a very high cost of ownership that does not become apparent until the drum requires replacement.

           Duplex printing (printing on both sides of the paper) can halve paper costs and reduce filing volumes. Formerly only available on high-end printers, duplexers are now common on mid-range office printers, though not all printers can accommodate a duplexing unit. Duplexing can also give a slower page-printing speed, because of the longer paper path.

Color laser printers

         Color laser printers use colored toner (dry ink), typically cyan, magenta, yellow, and black (CMYK). While monochrome printers only use one laser scanner assembly, color printers often have two or more.

Color laser Printer

         Color printing adds complexity to the printing process because very slight misalignments known as registration errors can occur between printing each color, causing unintended color fringing, blurring, or light/dark streaking along the edges of colored regions. To permit a high registration accuracy, some color laser printers use a large rotating belt called a "transfer belt". The transfer belt passes in front of all the toner cartridges and each of the toner layers are precisely applied to the belt. The combined layers are then applied to the paper in a uniform single step.

         Color printers usually have a higher cost per page than monochrome printers (even if printing monochrome-only pages).

Comparison with inkjet printers

        Manufacturers use a similar business model for both low-cost color laser printers and inkjet printers: the printers are sold cheaply while replacement toners and inks are relatively expensive. Color laser printers are much quicker than inkjet printers and their running cost per page is usually slightly less. The print quality of color lasers is limited by their resolution, typically 600–1200 dpi, and their use of just four color toners. They often have trouble printing large areas of the same or gradually changing color. Inkjet printers designed for printing photos can produce much higher quality color images.

Anti-counterfeiting marks

           Many modern color laser printers mark printouts by a nearly invisible dot raster, for the purpose of identification.

            The dots are yellow and about 0.1 mm (0.0039 in) in size, with a raster of about 1 mm (0.039 in). This is purportedly the result of a deal between the U.S. government and printer manufacturers to help track counterfeiters.

         The dots encode data such as printing date, time, and printer serial number in binary-coded decimal on every sheet of paper printed, which allows pieces of paper to be traced by the manufacturer to identify the place of purchase, and sometimes the buyer.

         Digital rights advocacy groups such as the Electronic Frontier Foundation are concerned about this erosion of the privacy and anonymity of those who print.

Smart chips in toner cartridges

        Similar to inkjet printers, toner cartridges may contain smart chips that reduce the number of pages that can be printed with it (reducing the amount of usable ink in the cartridge to sometimes only 50%, in an effort to increase sales of the toner cartridges. Besides being more expensive to the consumer, this technique also increases waste, and thus increases pressure on the environment. For these toner cartridges (as with inkjet cartridges), reset devices can be used to override the limitation set by the smart chip. Also, for some printers, online walk-through have been posted to demonstrate how to use up all the ink in the cartridge.


Toner clean-up

           Toner particles are designed to have electrostatic properties and can develop static electric charges when they rub against other particles, objects, or the interiors of transport systems and vacuum hoses. Static discharge from charged toner particles can ignite dust in a vacuum cleaner bag or create a small explosion if sufficient toner is airborne. Toner particles are so fine that they are poorly filtered by conventional household vacuum cleaner filter bags and blow through the motor or back into the room.

          If toner spills into the laser printer, a special type of vacuum cleaner with an electrically conductive hose and a high efficiency (HEPA) filter may be needed for effective cleaning. These are called ESD-safe (Electrostatic Discharge-safe) or toner vacuums. Similar HEPA-filter equipped vacuums should be used for clean-up of larger toner spills.

Ozone hazards

          As a normal part of the printing process, the high voltages inside the printer can produce a corona discharge that generates a small amount of ionized oxygen and nitrogen, forming ozone and nitrogen oxides. In larger commercial printers and copiers, a carbon filter in the air exhaust stream breaks down[citation needed] these oxides to prevent pollution of the office environment.

          However, some ozone escapes the filtering process in commercial printers, and ozone filters are not used in many smaller consumer printers. When a laser printer or copier is operated for a long period of time in a small, poorly ventilated space, these gases can build up to levels at which the odor of ozone or irritation may be noticed. A potential for creating a health hazard is theoretically possible in extreme cases.

Respiratory health risks

         According to a recent study conducted in Queensland, Australia, some printers emit sub-micrometre particles which some suspect may be associated with respiratory diseases. Of 63 printers evaluated in the Queensland University of Technology study, 17 of the strongest emitters were made by HP and one by Toshiba. The machine population studied, however, was only those machines already in place in the building and was thus biased toward specific manufacturers. The authors noted that particle emissions varied substantially even among the same model of machine. According to Professor Morawska of Queensland University, one printer emitted as many particles as a burning cigarette:

         The health effects from inhaling ultrafine particles depend on particle composition, but the results can range from respiratory irritation to more severe illness such as cardiovascular problems or cancer.

 Queensland University of Technology

          Muhle et al. (1991) reported that the responses to chronically inhaled copying toner, a plastic dust pigmented with carbon black, titanium dioxide and silica were also similar qualitatively to titanium dioxide and diesel exhaust.

          In December 2011, the Australian government agency Safe Work Australia reviewed existing research and concluded that "no epidemiology studies directly associating laser printer emissions with adverse health outcomes were located" and that several assessments conclude that "risk of direct toxicity and health effects from exposure to laser printer emissions is negligible". The review also observes that, because the emissions have been shown to be volatile or semi-volatile organic compounds, "it would be logical to expect possible health effects to be more related to the chemical nature of the aerosol rather than the physical character of the ‘particulate’ since such emissions are unlikely to be or remain as ‘particulates’ after they come into contact with respiratory tissue."

Air transport ban

           After the 2010 cargo plane bomb plot, in which shipments of laser printers with explosive-filled toner cartridges were discovered on separate cargo airplanes, the US Transportation Security Administration prohibited pass-through passengers from carrying toner or ink cartridges weighing over 1 pound (0.45 kg) on inbound flights, in both carry-on and checked luggage. PC Magazine noted that the ban would not impact most travelers, as the majority of cartridges do not exceed the proscribed weight.

Inkjet printer

Inkjet printer
       The inkjet printer, which is also known as the bubble jet, was first introduced in 1976, but it took until the late 1980s before it become popular with home users, largely because of its printing problems and its cost. Inkjet printers create a printed image by spraying small droplets of very quick-drying ink through tiny nozzles (jets) onto the paper. The image quality on a monitor, is measured in dots per inch (dpi). The number of dots of ink used in a square inch of paper, the higher the print quality will be. For the most part, inkjet printers produce a better quality print than a dot matrix printer at roughly the same cost.

         Liquid ink cartridge from Hewlett-Packard HP 845C inkjet printer
Inkjet printers operate by propelling variably sized droplets of liquid ink onto almost any sized page. They are the most common type of computer printer used by consumers.

Dot Matrix Printer

Dot Matrix Printer

              Dot matrix printer was by far most popular printer for PC systems. Compared to its predecessors, daisy wheel printers and adapted electric typewriters, it was faster, relatively quieter, included more fonts and print sizes, and offered flexibility for cut-sheet paper or continuous-feed paper and forms. For these same reasons, dot matrix printers are still in use in many offices. Dot matrix printers for PCs have two standard sizes: narrow and wide. A narrow width printer is usually limited to 80 columns and is  typically used only for correspondence or forms. A wider dot matrix printer has a 132-column width and can e used as a general printer.

Dot Matrix Printer

              Compared to inkjet and laser printers, dot matrix printers are slow and noisy. However, in environments where printing on multi-part or continuous-feed preprinted forms is more important than the printer's noise or speed, dot matrix printers continue to thrive. For this reason, you will commonly see dot matrix printers in pharmacies, receiving docks, warehouses, and other administrative offices etc.

             

              sample output from 9-pin dot matrix printer (one character expanded to show detail)

The term dot matrix printer is used for impact printers that use a matrix of small pins to transfer ink to the page. The advantage of dot matrix over other impact printers is that they can produce graphical images in addition to text; however the text is generally of poorer quality than impact printers that use letter-forms (type).

Dot-matrix printers can be broadly divided into two major classes:

• Ballistic wire printers
• Stored energy printers

Dot matrix printers can either be character-based or line-based (that is, a single horizontal series of pixels across the page), referring to the configuration of the print head.

                In the 1970s & 80s, dot matrix printers were one of the more common types of printers used for general use, such as for home and small office use. Such printers normally had either 9 or 24 pins on the print head (early 7 pin printers also existed, which did not print descenders). There was a period during the early home computer era when a range of printers were manufactured under many brands such as the Commodore VIC-1525 using the Seikosha Uni-Hammer system. This used a single solenoid with an oblique striker that would be actuated 7 times for each column of 7 vertical pixels while the head was moving at a constant speed. The angle of the striker would align the dots vertically even though the head had moved one dot spacing in the time. The vertical dot position was controlled by a synchronised longitudinally ribbed platen behind the paper that rotated rapidly with a rib moving vertically seven dot spacings in the time it took to print one pixel column. 24-pin print heads were able to print at a higher quality and started to offer additional type styles and were marketed as Near Letter Quality by some vendors. Once the price of inkjet printers dropped to the point where they were competitive with dot matrix printers, dot matrix printers began to fall out of favour for general use.

              Some dot matrix printers, such as the NEC P6300, can be upgraded to print in colour. This is achieved through the use of a four-colour ribbon mounted on a mechanism (provided in an upgrade kit that replaces the standard black ribbon mechanism after installation) that raises and lowers the ribbons as needed. Colour graphics are generally printed in four passes at standard resolution, thus slowing down printing considerably. As a result, colour graphics can take up to four times longer to print than standard monochrome graphics, or up to 8-16 times as long at high resolution mode.

             Dot matrix printers are still commonly used in low-cost, low-quality applications such as cash registers, or in demanding, very high volume applications like invoice printing. Impact printing, unlike laser printing, allows the pressure of the print head to be applied to a stack of two or more forms to print multi-part documents such as sales invoices and credit card receipts using continuous stationery with carbonless copy paper. Dot-matrix printers were being superseded even as receipt printers after the end of the twentieth century.

Printer

Printer:

             The printer provides a means of permanently saving what the monitor can only display temporarily. For visual content, the monitor is capable of only temporarily holding its contents and only until the next visual image comes along.

      

      In computing, a printer is a peripheral which makes a persistent human readable representation of graphics or text on paper or similar physical media. The two most common printer mechanisms are black and white laser printers used for common documents, and color inkjet printers which can produce high quality photograph output.

The world's first computer printer was a 19th-century mechanically driven apparatus invented by Charles Babbage for his difference engine. This system used a series of metal rods with characters printed on them and stuck a roll of paper against the rods to print the characters. The first commercial printers generally used mechanisms from electric typewriters and Teletype machines, which operated in a similar fashion. The demand for higher speed led to the development of new systems specifically for computer use. Among the systems widely used through the 1980s were daisy wheel systems similar to typewriters, line printers that produced similar output but at much higher speed, and dot matrix systems that could mix text and graphics but produced relatively low-quality output. The plotter was used for those requiring high quality line art like blueprints.

The introduction of the low-cost laser printer in 1984 with the first HP LaserJet, and the addition of PostScript in next year's Apple LaserWriter, set off a revolution in printing known as desktop publishing. Laser printers using PostScript mixed text and graphics, like dot-matrix printers, but at quality levels formerly available only from commercial typesetting systems. By 1990, most simple printing tasks like fliers and brochures were now created on personal computers and then laser printed; expensive offset printing systems were being dumped as scrap. The HP Deskjet of 1988 offered the same advantages as laser printer in terms of flexibility, but produced somewhat lower quality output (depending on the paper) from much less expensive mechanisms. Inkjet systems rapidly displaced dot matrix and daisy wheel printers from the market. By the 2000s high-quality printers of this sort had fallen under the $100 price point and became commonplace.

The rapid update of internet email through the 1990s and into the 2000s has largely displaced the need for printing as a means of moving documents, and a wide variety of reliable storage systems means that a "physical backup" is of little benefit today. Even the desire for printed output for "offline reading" while on mass transit or aircraft has been displaced by e-book readers and tablet computers. Today, traditional printers are being used more for special purposes, like printing photographs or artwork, and are no longer a must-have peripheral.

Starting around 2010, 3D printing became an area of intense interest, allowing the creation of physical objects with the same sort of effort as an early laser printer required to produce a brochure. These devices are in their earliest stages of development and have not yet become commonplace.

Sound Card

Sound Card
              Today, sound is an inherent part of the PC. There are a variety of components common to virtually all PC sound system: a sound card, an amplifier, speakers, shielding, and drivers and specialized software. The sound card, also known as an audio adapter, is an expansion card that adds the ability to record and play back sound from internal or external sources. The sound card integrates all of the elements required to capture and reproduce sound. The elements of the sound card are the input, outputs, and signal processors, which are the 4 digital to audio converters (DACs) and analog to digital converters (ADCs) required to convert sound into or from digital data.
 
             The sound card typically includes jacks (connectors to accept sound inputs from a microphone or another sound source, such as a CD player or the like, and output jacks for speakers, amplifiers, or other sound recording equipment. Most sound cards are typically ISA or PCI adapter cards.However, the recent trend is to directly mount a sound chip on the motherboard, which eliminates the need for an audio adapter card.

Sound Card

            The components included on the sound card to convert sound into and out of digital data formats are as follows:

• Digital to analog converter (DAC): The DAC converts digital audio data from a hard drive or another storage medium into analog sound (normal everyday sound waves) that can be played back on the speakers or a set of headphones.
• Analog to digital converter (ADC): An ADC converts analog sound waves, such as a voice or a musical instrument, into digital data so it can be stored, edited, and transmitted.

• Analog inputs: Sound cards have two separate analog sound inputs: line level and microphone-level. Line-level inputs accept sound signals from electronic sources such as CD players or tape decks or signals that are directly input from a musical instrument, such as an electronic piano or a synthesizer. There are two separate inputs because microphones produce signals with a much lower voltage level than those from line-level sources. Mic-level inputs are generated from a stand-alone microphone or an amplified electric guitar plugged into the mic-level input. Line-level inputs are designed to handle the higher voltage signal produced by amplified electronic devices. The most common connector on analog inputs is the standard 1/8-inch phone jack that is just like those on the earphones of your portable CD or tape player. professional or more specialized sound cards may include left and right stereo RCA jacks, which are 1/4-inch phone jacks like the ones used to connect earphones to your home stereo components. The RCA jack, named for the early sound pioneering company, is the standard for professional studio equipment. Other important features and components found on most PC sound cards include:

• Analog outputs: Most sound cards have two analog output jacks. One, which is usually identified as Phones Out or Speaker Out, (or is marked with a picture to that effect) is powered by a small amplifier on the sound card that is capable of producing the sound for headphones or passive speakers. The other jack, usually labeled as the Line Out jack, produces a line-level signal that can be used as an input to a home-stereo receiver, for example. Like the analog input jacks, 1/8-inch phone jacks are the most common, but higher-end cards use RCA (1/4-inch) phone jacks.

• Digital I/O (input/output): This type of connector on a sound card makes it possible to accept input or send output directly to a digital device, such as a MiniDice or digital audio tape (DAT), without ever converting the data from digital to analog. This eliminates the need for the data to pass through either a DAC or an ADC, which always has the potential to degrade or distort the sound signal. It won't mean much to anyone except a sound engineer, but the most common digital interfaces used on sound cards are S/P-DIF (Sony/ Philips Digital Interface) and AES/EBU (Audio Engineering Society/European Broadcasting Union).

• Game/MIDI port: This connector is commonly used for game controllers such as joysticks or game pads. However, with a special type of cable, this port can be connected to any external MIDI (Musical Instrument Digital interface) device to send and receive MIDI data.

midi/game port

• Digital Signal Processor (DSP): Once found only on expensive high-end sound cards, the DSP chip serves only one purpose: to relieve the PC's CPU of the burden for processing audio data. As DSP chips become less expensive and are included in more and more devices, they are now finding their way onto less expensive sound cards. DSP chips are the fastest growing segment of the semiconductor industry as more demand is being generated for sound reproduction in smaller and smaller devices. Among the tasks performed by the DSP chip on a sound card are re-sampling (changing the bit depth and sample rate of audio data) and adding digital effects such as reverb and echo to an audio piece.

• Synthesizer: Unlike digital data that is sent through the DAC to be converted to sound, MIDI signals tell the sound card which sounds to make, at what frequency, and for how long. In order to play back MIDI sounds, the sound card must be able to generate these sounds using a synthesizer chip. Through MIDI signals, an external MIDI device can control the sound card's synthesizer chip. Synnthesizer chips vary widely in capabilities and sound quality, but many newer sound card now incorporate Wavetable that produces a higher quality sound by using digital samples of actual instruments in place of other synthesized sounds.

ISA Sound Cards
            Like other ISA expansion cards, ISA sound cards usually require some manual configuration to set the system resource assignments such as I/O port address, DMA, and IRQ for the card. These values are typically set with a series of jumper blocks on the card. Some cards require a combination of jumper settings and some entries in the AUTOEXEC.BAT and CONFIG.SYS files located in the root directory of the hard disk drive. The documentation and installation instructions that come with the card will specify the exact entries needed.
           ISA sound cards can be especially complicated to configure because they often use a separate set of values for different functions. For example, there are sound cards that require a separate port address, DMA, and IRQ for general use, another set of values for sound Blaster emulation, and a third set of values for MPU-401 emulation. That's nine resources to configure for a single expansion card! As you can see, there is no universal set of steps for configuring an ISA sound card. The only way to know exactly what values need to be assigned and how to assign them is to refer to the manufacturer's documentation. If the manual for the card is unavailable, many sound card manufacturers publish installation guides on their Web sites.

ISA sound card

PCI Sound Cards
            Many of the difficulties associated with configuring an ISA sound card are eliminated with PCI sound cards. Although there are still a number of resources that need to be assigned, this is typically accomplished by the Plug-and-Play BIOS in conjunction with an operating system that supports Plug and play, like Windows 95/98/2000. In most of these cases, certain system resources, such as IRQ and DMA, cannot be assigned manually.

PCI Sound Card

A few conditions must be met before a PCI card can be installed:

• There must be an available PCI slot.
• Many older motherboards use an earlier revision of the PCI BIOS that may not be compatible with newer sound cards. Check with the motherboard manufacturer if you have an older PCI motherboard and are not certain that the PCI BIOS revision may be less than version 2.1.
• Motherboard manufacturers commonly develop system BIOS updates after the motherboard is released. Sometimes these updates are designed to address issues such as Plug-and-Play device enumeration that can affect whether or not a card is successfully installed. Check with your motherboard manufacturer to see if there are any critical BIOS updates available. Always use caution when upgrading a system BIOS.

Installing a Sound Card

• Power down the system before opening the case. On ATX systems you may have to press and hold the power button for several seconds before it turns off. Check that there are no lights illuminated on the front of the case and no fans spinning.
•  Always use and anti-static wrist strap when working inside the PC to prevent damage from ESD (electrostatic-discharge).
•  Avoid using magnetized screwdrivers while working inside the PC.
• Do not contact the surface of the printed circuit board (PCB) on the motherboard or other adapter cards with your tools, or you may damage the boards.
•  Before closing the case, check to see that all expansion cards, RAM modules, and cable connections are still firmly in place.

Amplifier

Amplifier

           After digital audio data is converted into an audible (analog) signal, it must be amplified before it can be played back on speakers or headphones. Nearly all sound cards have an amplifier that can produce a sound level compatible with a set of headphones or a set of small PC speakers. Because the amplifier on the sound card is usually weak, PC speaker systems may include an amplifier in one or both of its speakers to enhance the sound. By adding the correct cabling and jacks, the sound card's output signal can be sent to your home stereo or home theater, in case you desire very high quality sound reproduction.



Speakers
            Like all speakers, PC speakers are categorized into two general groups: passive and active passive speakers do not include an amplifier; active speakers do. A passive speaker, which is what most standard PC speakers are, receives a signal that has been amplified enough to generate motion in the speaker's diaphragm and proface sound. An active speaker includes a built-in amplifier and typically does not require external amplifiers. An active speaker can accept low-level (line-level) signals. Nearly all PC speakers are passive speakers, with the exception of subwoorers. subwoofers. Subwoofers are speakers that generate only very low frequency sounds, like bass tones. A subwoofers are speakers that amplifier, which makes it an active speaker. The benefit of having a subwoofer on your system is that it will handle all of the low bass sounds, leaving the system's passive speakers and the amplifiers driving them to handle higher-level sounds, which are much easier to reproduce.

Speakers

           PC speakers come in a wide range of configurations, from small passive systems powered by the sound card's headphone output to active three-way and surround-sound systems that would rival many home theaters. Some PC monitors have integrated speakers either incorporated into their cases or designed to attach to its sides. The speakers I have been discussing to this point all connect to the PC cia the sound card using 1/8-inch jacks. However, the USB (Universal Serial Bus) speaker system is a recent development. USB speaker systems do not require that a sound card be installed in the PC. Digital audio is sent directly to the speakers via the USB cable, and all signal processing is done within the speaker enclosure itself, outside of the pC. There are many advantages to this type of system, not the least of which are the available expansion slot and reduced sound distortion from the other components inside the PC, but there are also disadvantages.
             One major disadvantage of USB speakers is that there are no input jacks that can be used to connect external or internal devices like a CD-ROM or DVD player.