Monthly Archives: July 2017

Computer speakers

Computer speakers are speakers external to a computer. Speakers contain amplifiers which vibrate to produce the sound. They come in many different forms. Some speakers are already attached to a computer. Some speakers are wireless. They work by Bluetooth.

Computer speakers, are speakers sold for use with computers, although usually capable of other audio uses, e.g. for an MP3 player. Most such speakers have an internal amplifier and consequently require a power source, which may be by a mains power supply often via an AC adapter, batteries, or a USB port (able to supply no more than 2.5W DC, 500mA at 5V). The signal input connector is often a 3.5 mm jack plug (usually color-coded lime green per the PC 99 standard); RCA connectors are sometimes used, and a USB port may supply both signal and power (requiring additional circuitry, and only suitable for use with a computer). Battery-powered wireless Bluetooth speakers require no connections at all. Most computers have speakers of low power and quality built in; when external speakers are connected they disable the built-in speakers. Altec Lansing claims to have created the computer speaker market in 1990.

Computer speakers range widely in quality and in price. Computer speakers sometimes packaged with computer systems are small, plastic, and have mediocre sound quality. Some computer speakers have equalization features such as bass and treble controls. More sophisticated computer speakers can have a subwoofer unit, to enhance bass output. The larger subwoofer enclosure usually contains the amplifiers for the subwoofer and the left and right speakers. Some computer displays have rather basic speakers built-in. Laptop computers have built-in integrated speakers, usually small and of restricted sound quality to conserve space.

Instead of using a computer speaker for better sound, a computer can be connected to any external sound system, typically a high-power high-quality setup. An unusual design by HiWave Technologies, the DyadUSB USB-powered stereo audio amplifier module used in the SoundScience QSB 30W Portable USB Speakers allows a USB-powered and driven stereo speaker pair to supply 30W of power for short periods with a signal that has short high-power peaks and much lower average power, as most music and speech does. It stores energy from the USB connection during quieter periods, delivering high power for the peaks. (With a constant sine-wave input, power output cannot exceed the 2.5W that any USB speaker can deliver). The module is claimed to require less power most of the time, increasing laptop computer battery endurance, and delivering clean, unclipped sound peaks.

Monitor Computer

computer monitor is an output device which displays the information in pictorial form. A monitor usually comprises the display device, circuitry, casing, and power supply. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD) with LED backlighting having replaced cold-cathode fluorescent lamp (CCFL) backlighting. Originally, computer monitors were used for data processing while television receivers were used for entertainment. From the 1980s onwards, computers (and their monitors) have been used for both data processing and entertainment, while televisions have implemented some computer functionality.

Early electronic computers were fitted with a panel of light bulbs where the state of each particular bulb would indicate the on/off state of a particular register bit inside the computer. This allowed the engineers operating the computer to monitor the internal state of the machine, so this panel of lights came to be known as the ‘monitor’. As early monitors were only capable of displaying a very limited amount of information, and were very transient, they were rarely considered for program output. Instead, a line printer was the primary output device, while the monitor was limited to keeping track of the program’s operation. As technology developed engineers realized that the output of a CRT display was more flexible than a panel of light bulbs and eventually, by giving control of what was displayed to the program itself, the monitor itself became a powerful output device in its own right.

On two-dimensional display devices such as computer monitors the display size or view able image size is the actual amount of screen space that is available to display a picture, video or working space, without obstruction from the case or other aspects of the unit’s design. The main measurements for display devices are: width, height, total area and the diagonal.

The size of a display is usually by monitor manufacturers given by the diagonal, i.e. the distance between two opposite screen corners. This method of measurement is inherited from the method used for the first generation of CRT television, when picture tubes with circular faces were in common use. Being circular, it was the external diameter of the glass envelope that described their size. Since these circular tubes were used to display rectangular images, the diagonal measurement of the rectangular image was smaller than the diameter of the tube’s face (due to the thickness of the glass). This method continued even when cathode ray tubes were manufactured as rounded rectangles; it had the advantage of being a single number specifying the size, and was not confusing when the aspect ratio was universally 4:3.

With the introduction of flat panel technology, the diagonal measurement became the actual diagonal of the visible display. This meant that an eighteen-inch LCD had a larger visible area than an eighteen-inch cathode ray tube. The estimation of the monitor size by the distance between opposite corners does not take into account the display aspect ratio, so that for example a 16:9 21-inch (53 cm) widescreen display has less area, than a 21-inch (53 cm) 4:3 screen. The 4:3 screen has dimensions of 16.8 in × 12.6 in (43 cm × 32 cm) and area 211 sq in (1,360 cm2), while the widescreen is 18.3 in × 10.3 in (46 cm × 26 cm), 188 sq in (1,210 cm2).


In computing, a computer keyboard is a typewriter-style device which uses an arrangement of buttons or keys to act as a mechanical lever or electronic switch. Following the decline of punch cards and paper tape, interaction via teleprinter-style keyboards became the main input device for computers. A keyboard typically has characters engraved or printed on the keys (buttons) and each press of a key typically corresponds to a single written symbol.

Despite the development of alternative input devices, such as the mouse, touchscreen, pen devices, character recognition and voice recognition, the keyboard remains the most commonly used device for direct (human) input of alphanumeric data into computers. In normal usage, the keyboard is used as a text entry interface to type text and numbers into a word processor, text editor or other programs. In a modern computer, the interpretation of key presses is generally left to the software. A computer keyboard distinguishes each physical key from every other and reports all key presses to the controlling software. Keyboards are also used for computer gaming, either with regular keyboards or by using keyboards with special gaming features, which can expedite frequently used keystroke combinations. A keyboard is also used to give commands to the operating system of a computer, such as Windows’ Control-Alt-Delete combination, which brings up a task window or shuts down the machine. A command-line interface is a type of user interface operated entirely through a keyboard, or another device doing the job of one.

There are a number of different arrangements of alphabetic, numeric, and punctuation symbols on keys. These different keyboard layoutsarise mainly because different people need easy access to different symbols, either because they are inputting text in different languages, or because they need a specialized layout for mathematics, accounting, computer programming, or other purposes. The United States keyboard layout is used as default in the currently most popular operating systems: Windows, Mac OS X and Linux. The common QWERTY-based layout was designed early in the era of mechanical typewriters, so its ergonomics were compromised to allow for the mechanical limitations of the typewriter.

As the letter-keys were attached to levers that needed to move freely, inventor Christopher Sholes developed the QWERTY layout to reduce the likelihood of jamming. With the advent of computers, lever jams are no longer an issue, but nevertheless, QWERTY layouts were adopted for electronic keyboards because they were widely used. Alternative layouts such as the Dvorak Simplified Keyboard are not in widespread use. The QWERTZ layout is widely used in Germany and much of Central Europe. The main difference between it and QWERTY is that Y and Z are swapped, and most special characters such as brackets are replaced by diacritical characters.

Alphabetical, numeric, and punctuation keys are used in the same fashion as a typewriter keyboard to enter their respective symbol into a word processing program, text editor, data spreadsheet, or other program. Many of these keys will produce different symbols when modifier keys or shift keys are pressed. The alphabetic characters become uppercase when the shift key or Caps Lock key is depressed. The numeric characters become symbols or punctuation marks when the shift key is depressed. The alphabetical, numeric, and punctuation keys can also have other functions when they are pressed at the same time as some modifier keys. The Space bar is a horizontal bar in the lowermost row, which is significantly wider than other keys. Like the alphanumeric characters, it is also descended from the mechanical typewriter. Its main purpose is to enter the space between words during typing. It is large enough so that a thumb from either hand can use it easily. Depending on the operating system, when the space bar is used with a modifier key such as the control key, it may have functions such as resizing or closing the current window, half-spacing, or backspacing. In computer games and other applications the key has myriad uses in addition to its normal purpose in typing, such as jumping and adding marks to check boxes. In certain programs for playback of digital video, the space bar is used for pausing and resuming the playback.



A computer mouse is an input device that is most often used with a personal computer. Moving a mouse along a flat surface can move the on-screen cursor to different items on the screen. Items can be moved or selected by pressing the mouse buttons (called clicking). It is called a computer mouse because of the wire that connects the mouse to the computer. The people who designed the first computer mice thought that it looked like the tail on a mouse. Today, many computer mice use wireless technology and have no wire.

In 1964 Douglas Engelbart (1925-2013), a researcher at Stanford Research Institute, wanted to find a way to make using computers easier. In those days, computers were large and expensive. Using them was very hard because everything had to be typed in by hand, and there was no way to alter things if you made a mistake. After studying and designing for a long time, Engelbart succeeded in inventing an input device which he named ‘XY index’. At first, it needed two hands to use, but it was changed so that only one hand was needed to use it. This model was more like the mouse that we use today. Xerox Palo Alto Research introduced a GUI in 1981, using a mouse. The mouse was used with Macintosh of Apple Inc. when it came out in 1984. Microsoft Windows also used the mouse when it came out, so over time computer mice became used with many computers. Modern mice have three buttons: left button, right button, scroll button.

A mouse typically controls the motion of a pointer in two dimensions in a graphical user interface (GUI). The mouse turns movements of the hand backward and forward, left and right into equivalent electronic signals that in turn are used to move the pointer.

The relative movements of the mouse on the surface are applied to the position of the pointer on the screen, which signals the point where actions of the user take place, so hand movements are replicated by the pointer. Clicking or hovering (stopping movement while the cursor is within the bounds of an area) can select files, programs or actions from a list of names, or (in graphical interfaces) through small images called “icons” and other elements. For example, a text file might be represented by a picture of a paper notebook and clicking while the cursor hovers this icon might cause a text editing program to open the file in a window.

Different ways of operating the mouse cause specific things to happen in the GUI:

  • Click: pressing and releasing a button.
    • (left) Single-click: clicking the main button.
    • (left) Double-click: clicking the button two times in quick succession counts as a different gesture than two separate single clicks.
    • (left) Triple-click: clicking the button three times in quick succession counts as a different gesture than three separate single clicks. Triple clicks are far less common in traditional navigation.
    • Right-click: clicking the secondary button, or clicking with two fingers. (This brings a menu with different options depending on the software)
    • Middle-click: clicking the tertiary button.
  • Drag and drop: pressing and holding a button, then moving the mouse without releasing. (Using the command “drag with the right mouse button” instead of just “drag” when one instructs a user to drag an object while holding the right mouse button down instead of the more commonly used left mouse button.)
  • Mouse button chording (a.k.a. Rocker navigation).
    • Combination of right-click then left-click.
    • Combination of left-click then right-click or keyboard letter.
    • Combination of left or right-click and the mouse wheel.
  • Clicking while holding down a modifier key.
  • Moving the pointer a long distance: When a practical limit of mouse movement is reached, one lifts up the mouse, brings it to the opposite edge of the working area while it is held above the surface, and then replaces it down onto the working surface. This is often not necessary, because acceleration software detects fast movement, and moves the pointer significantly faster in proportion than for slow mouse motion.
  • Multi-touch: this method is similar to a multi-touch trackpad on a laptop with support for tap input for multiple fingers, the most famous example being the Apple Magic Mouse.