A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device (a touchpad, also known as a trackpad, and/or a pointing stick) and speakers into a single unit. A laptop is powered by mains electricity via an AC adapter, and can be used away from an outlet using a rechargeable battery.
Portable computers, originally monochrome CRT-based and developing into the modern laptops, and were originally considered to be a small niche market, mostly for specialized field applications such as the military, accountants and sales representatives. As portable computers became smaller, lighter, cheaper, more powerful and as screens became larger and of better quality, laptops became very widely used for all sorts of purposes.History
Main article: History of laptops
Alan Kay with “Dynabook” prototype
The Epson HX-20
As the personal computer became feasible in the early 1970s, the idea of a portable personal computer followed. A “personal, portable information manipulator” was imagined by Alan Kay at Xerox PARC in 1968, and described in his 1972 paper as the “Dynabook”.
The IBM SCAMP project (Special Computer APL Machine Portable), was demonstrated in 1973. This prototype was based on the PALM processor (Put All Logic In Microcode).
The IBM 5100, the first commercially available portable computer, appeared in September 1975, and was based on the SCAMP prototype.
As 8-bit CPU machines became widely accepted, the number of portables increased rapidly. The Osborne 1, released in 1981, used the Zilog Z80 and weighed 23.6 pounds (10.7 kg). It had no battery, a 5 in (13 cm) CRT screen, and dual 5.25 in (13.3 cm) single-density floppy drives. In the same year the first laptop-sized portable computer, the Epson HX-20, was announced. The Epson had a LCD screen, a rechargeable battery, and a calculator-size printer in a 1.6 kg (3.5 lb) chassis. Both Tandy/RadioShack and HP also produced portable computers of varying designs during this period.
The first laptops using the flip form factor appeared in the early 1980s. The Dulmont Magnum was released in Australia in 1981–82, but was not marketed internationally until 1984–85. The $8,150 ($18,540 today) GRiD Compass 1100, released in 1982, was used at NASA and by the military among others. The Gavilan SC, released in 1983, was the first computer described as a “laptop” by its manufacturer From 1983 onward, several new input techniques were developed and included in laptops, including the touchpad (Gavilan SC, 1983), the pointing stick (IBM ThinkPad 700, 1992) and handwriting recognition (Linus Write-Top, 1987). Some CPUs, such as the 1990 Intel i386SL, were designed to use minimum power to increase battery life of portable computers, and were supported by dynamic power management features such as Intel SpeedStep and AMD PowerNow! in some designs.
Displays reached VGA resolution by 1988 (Compaq SLT/286), and colour screens started becoming a common upgrade in 1991 with increases in resolution and screen size occurring frequently until the introduction of 17″-screen laptops in 2003. Hard drives started to be used in portables, encouraged by the introduction of 3.5″ drives in the late 1980s, and became common in laptops starting with the introduction of 2.5″ and smaller drives around 1990; capacities have typically lagged behind physically larger desktop drives. Optical storage, read-only CD-ROM followed by writeable CD and later read-only or writeable DVD and Blu-Ray, became common in laptops soon in the 2000s.Classification
The MacBook Air
The term “laptop” can refer to a number of classes of small portable computers:
A desktop replacement laptop with its 18.4 inch screen
Asus I7 High-Res Notebook
Full-size Laptop: A laptop large enough to accommodate a “full-size” keyboard (a keyboard with the minimum QWERTY key layout, which is at least 13.5 keys across that are on ¾ (0.750) inch centers, plus some room on both ends for the case). The measurement of at least 11 inches across has been suggested as the threshold for this class. The first laptops were the size of a standard U.S. “A size” notebook sheet of paper (8.5 × 11 inches), but later “A4-size” laptops were introduced, which were the width of a standard ISO 216 A4 sheet of paper (297 mm, or about 11.7 inches), and added a vertical column of keys to the right and wider screens.
Netbook: A smaller, lighter, more portable laptop. It is also usually cheaper than a full-size laptop, but has fewer features and less computing power. Smaller keyboards can be more difficult to operate. There is no sharp line of demarcation between netbooks and inexpensive small laptops; some 11.6″ models are marketed as netbooks. Since netbook laptops are quite small in size, CDs cannot be used in these computers.
Tablet PC: these have touch screens. There are “convertible tablets” with a full keyboard where the screen rotates to be used atop the keyboard, and “slate” form-factor machines which are usually touch-screen only (although a few older models feature very small keyboards along the sides of the screen.)
Rugged: Engineered to operate in tough conditions (mechanical shocks, extreme temperatures, wet and dusty environments).
Main article: Desktop replacement computer
A desktop-replacement computer is a laptop that provides all of the capabilities of a desktop computer, with a similar level of performance. Desktop replacements are usually larger and heavier than standard laptops. They contain more powerful components and have a 15″ or larger display. They are bulkier and not as portable as other laptops, and their operation time on batteries is typically shorter; they are intended to be used as compact and transportable alternatives to a desktop computer.
Some laptops in this class use a limited range of desktop components to provide better performance for the same price at the expense of battery life; a few of those models have no battery. 
In the early 2000s, desktops were more powerful, easier to upgrade, and much cheaper than laptops, but in later years laptops have become much cheaper and more powerful, and most peripherals are available in laptop-compatible USB versions which minimise the need for internal add-on cards. In the second half of 2008, laptops outsold desktops for the first time.
The names “Media Center Laptops” and “Gaming Laptops” are used to describe specialized notebook computers.
200pxSony VAIO P series subnotebook.
Main article: Subnotebook
A subnotebook or ultraportable, is a laptop designed and marketed with an emphasis on portability (small size, low weight and often longer battery life) that retains performance close to that of a standard notebook. Subnotebooks are usually smaller and lighter than standard laptops, weighing between 0.8 and 2 kg (2 to 5 pounds); the battery life can exceed 10 hours when a large battery or an additional battery pack is installed. Since the introduction of netbooks, the line between subnotebooks and higher-end netbooks has been substantially blurred.
To achieve the size and weight reductions, ultraportables use 13″ and smaller screens (down to 6.4″), have relatively few ports (but in any case include two or more USB ports), employ expensive components designed for minimal size and best power efficiency, and utilize advanced materials and construction methods. Most subnotebooks achieve a further portability improvement by omitting an optical/removable media drive; in this case they may be paired with a docking station that contains the drive and optionally more ports or an additional battery.
The term “subnotebook” is reserved to laptops that run general-purpose desktop operating systems such as Windows, Linux or Mac OS X, rather than specialized software such as Windows CE, Palm OS or Internet Tablet OS.
At Computex 2011 Intel announced a new class for ultraportables called ultrabooks. The term is used to describe a highly portable laptop that has strict limits for size, weight, battery life, and have tablet-like features such as instant on functionality. Intel estimates that by the end of 2012, 40 percent of the consumer laptop market segment will be Ultrabooks. 
Netbooks are laptops that are light-weight, economical, energy-efficient and especially suited for wireless communication and Internet access. Hence the name netbook (as “the device excels in web-based computing performance”).
With primary focus given to web browsing and e-mailing, netbooks are intended to “rely heavily on the Internet for remote access to web-based applications” and are targeted increasingly at cloud computing users who rely on servers and require a less powerful client computer. A common distinguishing feature is the lack of optical disk (i.e. CD, DVD or BluRay) drives. While the devices range in size from below 5 inches to over 12, most are between 9 and 11 inches (280 mm) and weigh between 0.9–1.4 kg (2–3 pounds).
Netbooks are mostly sold with light-weight operating systems such as Linux, Windows XP and Windows 7 Starter edition.
Because they’re very portable, Netbooks have a few disadvantages. Because the netbooks are thin, the first such products introduced to the market had their primary internal storage in the form of solid-state drives and not hard disks, which are essential to installing very many programs. Hard disk drive technology and form factors have since been adapted to fit into netbooks.
Given their size and use of more rudimentary components compared to notebooks and subnotebooks, netbooks also generally have a smaller-capacity hard drive, slower CPU, and a lower-profile RAM capacity.
Recently, Google has announced to be developing an own operating system called Chrome for this market.
The big breakthrough for netbook computers did not happen until the weight, diagonal form-factor and price combination of < 1 kg, < 9″, < U.S. $400, respectively, became commercially available at around 2008.