Almost all manufacturers have conceived their lap top computers to work with a keyboard and mouse, and they will also have a pad and or joystick that can be used to substitute for the mouse. Lap top computers come in three basic styles differing in size. An ultraportable laptop will generally weigh less than 1.7 kilograms, while a lightweight slim version will weigh up to 2.8 kilograms, and a larger size lap top will weigh up to 3.5 kilograms. The idea for the laptop existed prior to the invention of the personal computer, and was first conceived during the 1970s. The very first laptop was the Osborne 1, which was released in 1981.