Laptops usually run on a single main battery or from an external AC/DC adapter that charges the battery while also
supplying power to the computer itself even in the event of a power failure. This very powerful main battery should not be confused with smaller 3 volt cell battery that is built in nearly every computer. This small battery is intended to to run the real-time clock and backup BIOS configuration into the CMOS memory during the time the computer is not powered on and/or is not connected to the external 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), for instance, SO-DIMM in lieu of the larger DIMMs. 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.
HISTORY
Laptops began from a desire to have a full-featured computer that could be easily used anywhere. Their predecessor was called the luggable. These all-in-one systems could be easily transported, but were heavy and usually were not battery powered. The CRT was one of the major reasons luggables were so large and heavy, but the use of a full-size desktop motherboard with room for ISA expansion cards was another size factor.
It was the transition to LCD and plasma displays that permitted the luggable to shrink in size and become the first real laptop, though at first still without internal batteries. Battery technology improvements and the introduction of smaller devices such as the 3.5-inch floppy disk permitted a gradually more compact and sophisticated complete portable system.
DESKTOP REPLACEMENT
A desktop replacement computer is a personal computer that provides the full capabilities of a desktop computer while remaining portable. They are often a larger, bulkier laptop. Because of their increased size, this class of computer usually includes more powerful components and a larger display than generally used in smaller portable computers and can have a relatively limited battery capacity (or none at all). Some use a limited range of desktop components to provide better performance per dollar at the expense of battery life. These are sometimes called desknotes, a portmanteau of the wor
ds "desktop" and "notebook," though the term is also applied to desktop replacement computers in general.[1]Powerful laptops meant to be mainly used for fun and infrequently carried out due to their weight and size; the latter provides more space for powerful components and a big screen, usually measuring 17–20 inches (43–51 cm). Desktop replacements tend to have limited battery life, rarely exceeding three hours, because the hardware is not optimized for efficient power usage. Sometimes called a luggable laptop. An example of a desktop replacement computers are gaming notebooks, which are designed to handle 3D graphic-intensive processing for gamers.
SUBNOTEBOOK
Laptops weighing typically between 4.6 and 6 lb (1.8–2.7 kg) and a screen of 10.6 to 13.3 inches diagonally. A subnotebook is a small and lightweight portable computer, with most of the features of a standard laptop computer but smaller. The term is often applied to systems that run full versions of desktop operating systems such as Windows or Linux, rather than specialized software such as Windows CE, Palm OS or Internet Tablet OS.
Subnotebooks are smaller than laptops but larger than handheld computers and UMPCs. They often have screens around 10.6" (26.92 cm) (diagonal) and weigh less than 1 to 2 kg, as opposed to full-size laptops with 14.1" (35.81 cm) or 15.4" (39.12 cm) screens that typically weigh 2 kg or more. The savings in size and weight are usually achieved partly by omitting ports or having removable media/optical drives; subnotebooks are often paired with docking stations to compensate.
Subnotebooks have been something of a niche computing product and have rarely sold in large numbers until the 2007 introduction of the Asus Eee PC and the OLPC XO-1.[2]
