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A laptop computer

A laptop computer or laptop (also notebook computer, notebook and notepad) is a small mobile computer, typically weighing 3 to 12 pounds (1.4 to 5.4 kg), although older laptops may weigh more.

Laptops usually run on a single main battery or from an external AC/DC adapter that charges the battery while it also supplies power to the computer itself, even in the event of a power failure. This very powerful main battery should not be confused with the much smaller battery nearly all computers use to run the real-time clock and backup BIOS configuration into the CMOS memory when the computer is without power.

Laptops contain components that are similar to their desktop counterparts and perform the same functions, but are miniaturized and optimized for mobile use and efficient power consumption, although typically less powerful for the same price. Laptops usually have liquid crystal displays and most of them use different memory modules for their random access memory (RAM). In addition to a built-in keyboard, they may utilize a touchpad (also known as a trackpad) or a pointing stick for input, though an external keyboard or mouse can usually be attached.

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 price 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.

Arithmetic/logic unit (alu)

The ALU is capable of performing two classes of operations: arithmetic and logic.

The set of arithmetic operations that a particular ALU supports may be limited to adding and subtracting or might include multiplying or dividing, trigonometry functions (sine, cosine, etc) and square roots. Some can only operate on whole numbers (integers) whilst others use floating point to represent real numbers—albeit with limited precision. However, any computer that is capable of performing just the simplest operations can be programmed to break down the more complex operations into simple steps that it can perform. Therefore, any computer can be programmed to perform any arithmetic operation—although it will take more time to do so if its ALU does not directly support the operation. An ALU may also compare numbers and return Boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?").

Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful both for creating complicated conditional statements and processing Boolean logic.

Superscalar computers contain multiple ALUs so that they can process several instructions at the same time. Graphics processors and computers with SIMD and MIMD features often provide ALUs that can perform arithmetic on vectors and matrices.

Bits for pictures

Each tiny dot on the computer screen is called a picture element or pixel. Images and texts are formed by combining a large number of pixels. In a bit-mapped display the dots displayed on the screen correspond, pixel by pixel, with bits in the main memory on the computer. The bits are held in an area of the memory called the “refresh buffer” and are stored in groups that represent the horizontal and vertical position of the pixels on the screen and whether the pixels are “on” or “off”.

On monochrome systems, one bit in this “map” represents one pixel on the screen and can be either “on” or “off” (black or white).

On color systems each pixels is a certain combination of the three primary colors: red, green and blue. The total number of colors which can be shown on the screen is called the color palette. The size of this palette depends on the graphic adaptor a separate video card that converts the bits into visual signals. A graphic adaptor with 1 bit per primary color can generate up to 8 colors. A graphic adaptor with 8 bits per primary color can generate 16.7 million colors.

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