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In order to make use of a computer, some form of output devicesmust be used to allow the user to understand what is going on inside the machine.
A computer can produce sound in the form of beeps from the piezo speaker on its motherboard, or it can use a sound card to produce true tone sounds that sound like the real thing.
This is the primary method of sound output in most computers today. Sound is translated from bits to electrical signals in a sound card, which then channels the signals to the speakers.
MIDI (Musical Instrument Digital Interface), is an industry-standard protocol that enables electronic musical instruments (synthesizers, drum machines), computers and other electronic equipment (MIDI controllers, sound cards, samplers) to communicate and synchronize with each other. Unlike analog devices, MIDI does not transmit an audio signal — it sends event messages about pitch and intensity, control signals for parameters such as volume, vibrato and panning, cues, and clock signals to set the tempo.
MIDI files are typically created using computer-based sequencing software (or sometimes a hardware-based MIDI instrument or workstation) that organizes MIDI messages into one or more parallel "tracks" for independent recording and editing.
A microphone is a device used to change sound into electric signals. Microphones are used in telephones, tape recorders, hearing aids and many other devices.
A printer is a device that prints text or images, making a physical copy (usually with some kind of ink on paper). . Printers are classified into two types: impact and non-impact printers. Impact printers rely upon a mechanical impact to transfer ink to paper. Early printers were more like electric typewriters, striking an ink ribbon against the paper with a lever with a raised image of a letter on the end, or a rotating ball with the same. Non-impact printers depend on other ways of creating an image. Plotters, covered separately, can also be used as printers.
A laser printer directs a laser beam onto a rotating drum, covered by a photoconductor (a material that conducts electricity when illuminated), carrying an electrostatic charge. The laser "erases" the charge in areas it strikes. Then a powdered ink ("toner"), charged the same polarity as the original surface charge on the drum, is spread across the surface, and it is repelled from the areas that still carry the original charge, but it is attracted to the discharged areas where the image was "written" by the laser. The drum then rolls the image formed onto paper, which is then be heated ("fused") to make the toner stick to itself and the paper.
An inkjet printer is a type of computer printer that creates a digital image by propelling variably-sized droplets of liquid material (ink) onto a page. Inkjet printers are the most common type of printer and range from small inexpensive consumer models to very large and expensive professional machines.
A plotter is a vector graphics printing device that connects to a computer.
Vector graphics could be considered as points, lines, curves, and polygons, which are all based upon mathematical equations to represent images in computer graphics. Raster graphics, by comparison, are known to the computer as just a bunch of dots. Raster graphics lose their sharpness if made too big, but vector images can be expanded indefinitely.
Pen plotters print their output by moving a pen across the surface of a piece of paper. This means that plotters are restricted to line art, rather than raster graphics as with other printers. They can draw complex line art, including text, but do so very slowly because of the mechanical movement of the pens.
Early plotters worked by placing the paper over a roller which moved the paper back and forth for X motion, while the pen moved back and forth on a single arm for Y motion.
An electrostatic plotter produces a raster image by charging the paper with a high voltage. This voltage attracts toner which is then melted into the paper with heat.
This type of plotter is fast, but the quality is generally considered to be poor when compared to pen plotters.
A monitor or display (sometimes called a visual display unit) is an electronic visual display for computers.
Dot pitch 
A dot pitch (sometimes called line pitch, stripe pitch, phosphor pitch, or pixel pitch) is a specification for a computer display, computer printer, image scanner or other pixel-based device that describes the distance, for example, between dots (sub-pixels) of the same color on the inside of a display screen. In the case of a color display, dot pitch is a measure of the size of a triad plus the distance between the triads.
Dot pitch may be measured in linear units, usually millimeters, with a smaller number meaning closer spacing, or in dots per linear unit, for example dots per inch, with a larger number meaning closer spacing. Closer spacing generally produces a sharper image (as there are more pixels in a given area).
Resolution in monitors is measured in pixels. The amount of pixels and the size of the monitor can determine how sharp the picture is. Pixels are aligned in columns and rows in the display. The more pixels you have the better the display will be.
The resolution of scanners can vary by 1000's of DPI's (dots per inch). Resolution refers to the visuals of an image (for example, clarity and sharpness).
Colour depth 
The colour depth or bit depth is the number of bits used to represent the colour of a single pixel in a bitmapped image or video frame buffer. This concept is also known as bits per pixel (BPP), particularly when specified along with the number of bits used. Higher colour depth gives a broader range of distinct colours.
1 byte can produce 256 colours. Usually 2 or 3 bytes are used in images stored as photographs.
Refresh rate 
Refresh rate refers to the number of times the image on a monitor (screen) is redrawn each second. Essentially, it is the number of times per second that the pixels are recharged so that their glow remains bright. If the refresh rate is higher, the image on the screen will look more solid and flicker less. Typically, most screens have a refresh rate of between 56-120 times per second.
The cathode ray tube (CRT) is a vacuum tube containing an electron gun (a source of electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen. The image may represent electrical waveforms (oscilloscope), pictures (television, computer monitor), radar targets and others.
The CRT uses an evacuated glass envelope which is large, deep, heavy, and relatively fragile.
Flat panel 
Flat panel displays (usually called Flatscreen) encompass a growing number of technologies enabling video displays that are much lighter and thinner than traditional video displays that use cathode ray tubes, and are usually less than 100 mm (4 inches) thick.
Refers to the panel display, and can give us information about where their transistors are located. A passive-matrix display provides a sharp image for one-color (monochrome) screens, but is more subdued for color. By referring to passive-matrix display, this tells us that the transistor controls a whole row or column of pixels on the flat-screen display. The advantages to passive-matrix display are that they are less expensive and use less power. The most common abbreviations used to refer to passive-matrix are HPA, STN, and DSTN. ASQVXHYQABS QSIQNSBQ OUIHS OQP QIB-- PBS IAI IAB IIA IQIC DHE8D
Active-matrix LCD 
An active-matrix LCD is a type of liquid crystal display used in notebook computers as it is very portable and lightweight. It is also known as TFT (thin-film transistor). An active-matrix is both brighter and sharper than passive-matrix screens. They are more expensive and require more power which can affect battery life in portable computers.