A laptop computer or notebook computer 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 began from a desire to have a full-featured computer that could be
easily used anywhere. These all-in-one systems could be easily transported, but
were heavy and usually were not battery powered. The cathode ray tube (CRT) was
one of the major reasons portable computers were so large and heavy, but the use
of a full-size desktop motherboard with room for ISA expansion cards was another
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.
Most modern laptops feature 12 inch (30 cm) or larger active matrix displays
with resolutions of 1024◊768 pixels and above, and have a PC Card (formerly
PCMCIA) or ExpressCard expansion bay for expansion cards, one or more USB ports,
and a external monitor port (VGA or DVI). Most laptops have also an ethernet
network port. Some have legacy ports such as a PS/2 keyboard/mouse port or a
serial port, parallel port, and S-video or composite video port. Hard disks are
physically smalleró2.5 inch (60 mm)ócompared to the standard desktop 3.5 inch
(90 mm) drive, and usually have lower performance and power consumption. Video
and sound chips are usually integrated. This tends to limit the use of laptops
for gaming and entertainment, two fields which have constantly escalating
hardware demands, however, higher end laptops can come with dedicated
graphics processors. These mobile graphics processors tend to have less
performance than their desktop counterparts, but this is because they have been
optimized for lower power usage. Some subsystems, such as Wi-Fi, come in
contemporary laptops on replaceable MiniPCI cards, usually accessible through a
door on the bottom. Memory modules (smaller than the usual DIMMs) are often also
accessible through the bottom, though some may be on the motherboard under the
keyboard and thus not meant to be accessed by the user.
Laptops' upgradeability is severely limited, both for technical and economic
reasons. As of 2006, there is no industry-wide standard form factor for laptops.
Each major laptop vendor pursues its own proprietary design and construction,
with the result that laptops are difficult to upgrade and exhibit high repair
costs. With few exceptions, laptop components can rarely be swapped between
laptops of competing manufacturers, or even between laptops from the different
product-lines of the same manufacturer. Standard feature peripherals (such as
audio, video, USB, 1394, WiFi, Bluetooth) are generally integrated on the main
PCB (motherboard), and thus upgrades often require using external ports, card
slots, or wireless peripherals. Other components, such as RAM modules, hard
drives, and batteries are typically user-upgradeable.