PC Peripherals

Computer

A  computer is a device that accepts information (in the form of digital data) and manipulates it for some result based on a program or sequence of instructions on how data is to be processed. Complex computers also include the means for storing data (including the program, which is also a form of data) for some necessary duration. A program may be invariable and built into the computer (and called logic circuitry as it is on microprocessors) or different programs may be provided to the computer (loaded into its storage and then started by an administrator or user). Today's computers have both kinds of programming.

Most histories of the modern computer begin with the "Analytical Engine" envisioned by Charles Babbage following the mathematical ideas of George Boole, the mathematician who first stated the principles of logic inherent in today's digital computer. Babbage's assistant and collaborator, Ada Lovelace, is said to have introduced the ideas of program loops and subroutines and is sometimes considered the first programmer. Apart from mechanical calculators, the first really useable computers began with the vaccuum tube, accelerated with the invention of the transistor, which then became imbedded in large numbers in integrated circuits, ultimately making possible the relatively low-cost personal computer.

Monitor

In computers, a monitor is a computer display and related parts packaged in a physical unit that is separate from other parts of the computer. Notebook computers don't have monitors because all the display and related parts are integrated into the same physical unit with the rest of the computer. In practice, the terms monitor and display are used interchangably.

Printer

In computers, a printer is a device that accepts text and graphic output from a computer and transfers the information to paper, usually to standard size sheets of paper. Printers are sometimes sold with computers, but more frequently are purchased separately. Printers vary in size, speed, sophistication, and cost. Larger printers used in Fortune 500 companies can cost many thousands of dollars (U.S.) but can print at very high speeds - for example, a 300-page technical manual in 20 minutes. Personal computer printers under $500 print only a few pages a minute. In general, more expensive printers are used for higher-resolution color printing.

Personal computer printers can be distinguished as impact or non-impact printers. Early impact printers worked something like an automatic typewriter, with a key striking an inked impression on paper for each printed character. The dot-matrix printer has been a popular low-cost personal computer printer. It's an impact printer that strikes the paper a line at a time. The best-known non-impact printers are the inkjet printer, of which several makes of low-cost color printers are an example, and the laser printer. The inkjet sprays ink from an ink cartridge at very close range to the paper as it rolls by. The laser printer uses a laser beam reflected from a mirror to attract ink (called toner) to selected paper areas as a sheet rolls over a drum.

The four printer qualities of most interest to most users are:

Printer I/O Interfaces

The most common I/O interface for printers has been the parallel Centronics interface with a 36-pin plug. In the future, however, new printers and computers are likely to use a serial interface, especially USB or Fireware with a smaller and less cumbersome plug.

Printer Languages

Printer languages are commands from the computer to the printer to tell the printer how to format the document being printed. These commands manage font size, graphics, compression of data sent to the printer, color, etc. The two most popular printer languages are  Postscript and PCL.

Postscript is a printer language that uses English phrases and programmatic constructions to describe the appearance of a printed page to the printer. This printer language was developed by Adobe in 1985. It introduced new features such as outline fonts and Vector graphics. Printers now come from the factory with or can be loaded with Postscript support. Postscript is not restricted to printers. It can be used with any device that creates an image using dots such as screen displays, slide recorders, and image setters.

PCL (Printer Command Language) is an escape code language used to send commands to the printer for printing documents. Escape code language is so-called because the escape key begins the command sequence followed by a series of code numbers. Hewlett Packard originally devised PCL for dot matrix and inkjet printers. Since its introduction, it has become an industry standard. Other manufacturers who sell HP clones have copied it. Some of these clones are very good, but there are small differences in the way they print a page compared to real HP printers. In 1984, the original HP Laserjet printer was introduced using PCL. PCL helped change the appearance of low-cost printer documents from poor to exceptional quality.

Fonts

Fonts are characters of a specific style and size within an overall typeface design. Printers use resident fonts and soft fonts to print documents. Resident fonts are built into the hardware of a printer. They are also called internal fonts or built-in fonts. All printers come with one or more resident fonts. Additional fonts can be added by inserting a font cartridge into the printer or installing soft fonts to the hard drive. Resident fonts cannot be erased unlike soft fonts. Soft fonts are installed onto the hard drive and then sent to the computer's memory when a document is printed that uses the particular soft font. Soft fonts can be purchased in stores or downloaded from the Internet.

There are two types of fonts used by the printer and screen display,  bitmap fonts and outline fonts. Bitmap fonts are digital representations of fonts that are not scalable. This means they have a set size or a limited set of sizes. For example, if a document using a bitmap font sized to 24 point is sent to the printer and there is not a bitmap font of that size, the computer will try to guess the right size. This results in the text looking stretched-out or squashed. Jagged edges are also a problem with bitmap fonts. Outline fonts are mathematical descriptions of the font that are sent to the printer. The printer then rasterizes or converts them to the dots that are printed on the paper. Because they are mathematical, they are scalable. This means the size of the font can be changed without losing the sharpness or resolution of the printed text. TrueType and Type 1 fonts are outline fonts. Outline fonts are used with Postscript and PCL printer languages.

Scanner

A scanner captures images from photographic prints, posters, magazine pages, and similar sources for computer editing and display. Scanners come in hand-held, feed-in, and flatbed types and for scanning black-and-white only or color. Very high resolution scanners are used for scanning for high-resolution printing, but lower resolution scanners are adequate for capturing images for computer display. Scanners usually come with software, such as Adobe's Photoshop product, that lets you resize and otherwise modify a captured image.

Scanners usually attach to your personal computer with a Small Computer System Interface (SCSI). An application such as PhotoShop uses the TWAIN program to read in the image.

Keyboard

On most computers, a keyboard is the primary text input device. (The mouse is also a primary input device but lacks the ability to easily transmit textual information.) The keyboard also contains certain standard function keys, such as the Escape key, tab and cursor movement keys, shift and control keys, and sometimes other manufacturer-customized keys (CD Player, Shutdown, Standby, Sleep, Speaker, Scroll key, Short function keys etc) .

The computer keyboard uses the same key arrangement as the mechanical and electronic typewriter keyboards that preceded the computer. The standard arrangement of alphabetic keys is known as the QWERTY (pronounced KWEHR-tee) keyboard, its name deriving from the arrangement of the five keys at the upper left of the three rows of alphabetic keys. This arrangement, invented for one of the earliest mechanical typewriters, dates back to the 1870s. Another well-known key arrangement is the Dvorak (pronounced duh-VOR-ak, not like the Czech composer) system, which was designed to be easier to learn and use. The Dvorak keyboard was designed with the most common consonants on one side of the middle or home row and the vowels on the other side so that typing tends to alternate key strokes back and forth between hands. Although the Dvorak keyboard has never been widely used, it has adherents.

Because many keyboard users develop a cumulative trauma disorder,  such as carpal tunnel syndrome, a number of ergonomic keyboards have been developed. Approaches include keyboards contoured to alleviate stress and foot-driven pedals for certain keys or keyboard functions. For example Cordless Keyboard.

Mouse

A mouse is a small device that a computer user pushes across a desk surface in order to point to a place on a display screen and to select one or more actions to take from that position. The mouse first became a widely-used computer tool when Apple Computer made it a standard part of the Apple Macintosh. Today, the mouse is an integral part of the graphical user interface (GUI) of any personal computer. The mouse apparently got its name by being about the same size and color as a toy mouse.

A mouse consists of a metal or plastic housing or casing, a ball that sticks out of the bottom of the casing and is rolled on a flat surface, one or more buttons on the top of the casing, and a cable that connects the mouse to the computer. As the ball is moved over the surface in any direction, a sensor sends impulses to the computer that causes a mouse-responsive program to reposition a visible indicator (called a cursor) on the display screen. The positioning is relative to some variable starting place. Viewing the cursor's present position, the user readjusts the position by moving the mouse.

The most conventional kind of mouse has two buttons on top: the left one is used most frequently. In the Windows operating systems, it lets the user click once to send a "Select" indication that provides the user with feedback that a particular position has been selected for further action. The next click on a selected position or two quick clicks on it causes a particular action to take place on the selected object. For example, in Windows operating systems, it causes a program associated with that object to be started. The second button, on the right, usually provides some less-frequently needed capability. For example, when viewing a Web page, you can click on an image to get a popup menu that, among other things, lets you save the image on your hard disk. Some mice have a third button for additional capabilities. Some mouse manufacturers also provide a version for left-handed people.

Windows 95 and other operating systems let the user adjust the sensitivity of the mouse, including how fast it moves across the screen, and the amount of time that must elapse within a "double click.". In some systems, the user can also choose among several different cursor appearances. Some people use a mouse pad to improve traction for the mouse ball.

Mousepad

A mousepad is a small, portable surface that sometimes provides better traction for the ball on a computer mouse and, at the very least, provides a bounded area in which to move the mouse. On very smooth table or desktop surfaces, the mouse ball may tend to glide instead of roll unless pressure is continually applied. Some mousepads provide a slightly rougher surface so that it's easier to get the mouse to move the screen cursor. A mousepad usually has a plastic surface and a thin rubber or plastic cushion.

Mousepads are sometimes given away at computer and Internet trade shows or with Internet or computer magazine subscriptions.