One of the biggest problems for portable computers is heat buildup inside the case. Because conventional power supplies (and their fans) are not included in portable units, separate fans must be designed in portables to carry the heat out of the unit. The closeness of the portable's components and the small amount of free air space inside their cases also adds to heat-related design problems.
The internal PC boards of the portable computer are designed to fit around the nuances of the portable case and its components. Therefore, interchangeability of parts with other machines or makers is not possible most of the times. The only source of most portable computer parts, with the exception of PC Cards and disk drive units, is the original manufacturer. Even the battery case might be proprietary. If the battery dies, you must hope that the original maker has a supply of that particular model.
