Calculators And Watches

• Calculators and digital wristwatches get their power from small, coin-sized batteries. As it takes the device a year or two to drain a battery, the tiny computers in these gadgets are extremely thrifty with energy, using about .03 milliwatts, or thousandths of a watt, of energy per hour. Their computer chips are simple and run slowly compared with other devices, so they use as little power as possible.
  
  

Cellphone

• Even the simplest cell phone uses a computer chip to dial, manage calls and organize a personal contact directory. At the other end of the spectrum, many smartphones now play music and movies, browse the Web and send emails -- functions reserved for desktop computers only a few years ago. Cellphones, however, like watches, are powered by batteries; for all their power, they are still very efficient, using between .25 and 6 watts per hour, depending on whether the phone is in active use or relatively idle.
  
  

Notebook

• As with cellphones, notebook and netbook computers also run on batteries, though their batteries are several times larger than those used by cell phones. Notebooks perform more serious computing tasks, such as professional word processing and graphic design. They support more memory and run at faster speeds. They use between 20 and 60 watts per hour.
  
  

Desktop

• Though more people are opting for the portability and all-in-one convenience of notebook computers, desktop models run faster, have more memory and hard drive space. They have fewer compromises for energy efficiency and more raw computing power than notebooks, and are best at multitasking many programs at the same time. For these reasons, they consume more power than notebooks, between 75 and 200 watts per hour.
  
  

Server

• The fastest computers commercially sold are called servers. These systems handle hundreds to thousands of Web and database users, typically in large data networks. They have large amounts of memory and contain several microprocessors and disk drives. As they handle large amounts of work, they also consume the most electricity, from 500 to 1,200 watts per hour.