A notebook or laptop is nothing but a small portable computer that weighs 2.2 to 18 pounds (1 to 8 kg), that depends on its brand, style, size, material it is made of, and many other factors. Notebooks generally operate on a single main battery or through an external adapter that can both charge the battery and also supply power to the notebook. Notebooks are adept at performing the same jobs like a personal desktop; the only difference is that they are generally less powerful for the same cost. They consist of similar components like desktop computers and execute the same functions, except that they are miniature in size and suitable for transportable use and effective power consumption. Notebooks usually have LCD and different memory modules. They have a built-in keyboard; input is done through a touchpad or a pointing stick, though an external mouse can also be attached. There are different categories of notebooks. UMPCs are Ultra-Mobile PCs and are very portable. Since they are of a small size they can fit in a small touch screen while some other models have a minute physical keyboard along with a mouse interface. The other type is Ultraportables which are notebooks and have screens less than eleven inches and have less than 3.7 pounds (1.7 kg) of weight. They are generally used by business travelers, as they are small and light though very expensive. They have an extended battery life and integrated graphics. The other type of notebook is the Sony VAIO FJ76, and Dell XPS M1330 and XPS M1210. Then we have the mainstream notebooks that are more of budget desktops. And if you want desktop power, then you can opt for desktop replacement which can accommodate many performance components. As far as the processors are concerned you should go for the fastest that your budget will allow. You can opt for Intel`s Centrino that has great speed and also good battery life. Or else you can also go for the economic AMD`s mobile processors whose performance still lags behind Intel. If you intend to watch DVDs on your notebook then go for wide screen ones that offer sharper, larger and great images. The only consideration is that they are not meant for carrying around a lot. For great system performance it is vital to have enough memory (RAM) that will allow you to run many applications together. Adequate RAM is also essential for image and video editing, graphics work, and 3D gaming. Generally notebooks have a terrible sound quality so it is recommended to use speakers or headphones. These are some of the factors that you need to consider before buying a notebook. Also keep in mind that like any electronic device, your notebook is vulnerable to accidents as well as system failures. It is recommended to get at least a three year warranty and also some additional insurance. Health hazards related to using a laptop has been a controversial topic for quite some time. Researches have proved that heat generated from notebooks can raise temperature of scrotum, leading to reduced sperm count. A solution can be using it on a table or keeping it apart from the lap that will enable better cooling of the notebook and also prevent your lap from excessive electromagnetic radiation and heat. Some of the famous brands that have notebook are Acer that have TravelMate, Ferrari and Aspire models; BenQ; Compaq with its Armada, LTE, EVO and Presario models. Other famous brands are Gateway, HCL, Lenovo, LG, Micro-Star International, Panasonic, Samsung, Toshiba and others.