A laptop computer, or simply laptop (also notebook computer, notebook and notepad) is a small mobile computer, typically weighing 3-12 pounds (around 1.3 to 5.4 kilograms), 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 also supplying power to the computer itself. Many computers also have a 3 volt cell to run the clock and other processes in the event of a power failure.
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). Laptops rarely use the standard SIMM and DIMM memory modules used by non-portable machines. Instead, the laptop memory you may find are 72 pin SODimm (Small Outline Dual Inline Memory Module), 144 Pin SODimm (Small Outline Dual Inline Memory Module), DDR SDRAM (Dual Data Rate Synchronous RAM), SDRAM (Single data rate Synchronous RAM) and, proprietary memory modules
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.