Science & Technology in Action

6th Edition

Improving Energy Efficiency of Computers


The lesson examines the factors that determine energy use in computers and the steps that can be taken to minimise energy loss and extend battery life. Maximising the energy efficiency of computers entails reducing energy loss in each of the parts - power supply, processor, memory, screen etc.
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Lesson excerpt

Over the past fifty years the capability of computers (often called 'computing power') has increased dramatically while the physical size and electrical power requirements have decreased.

The lesson examines the factors that determine energy use in computers and the steps that can be taken to minimise energy loss and extend battery life.

The invention of the electric battery in 1800 made it possible to produce a steady electric current and many people began intensive study of its effects. The heating effect was quickly noted; wires carrying large electric currents could even melt. The chemical effect was also discovered and applied in electrolysis andelectroplating (1800). In 1820, while demonstrating the heating effect of an electric current, the Danish scientist Hans Christian Ørsted (Oersted) discovered that an electric current had amagnetic effect.

Electrical Resistance
Metals are generally good conductors of electricity; silver is the best followed closely by copper. However, all metals show someresistance to electric current and this gives rise to the heating effect. The resistance of a wire depends on the material, the length of the wire and its crosssectional area; long thinconductors have greater resistance than short thick ones. In 1849 James Joule discovered that the rate at which heat is produced, (i.e. the 'power') is proportional to the square of the current; this can be expressed concisely by the equation P=I2R, where P is the power, I is the current and R is the resistance.

The components in computers and other electronic devices are generally mounted on a 'printed circuit board' or PCB; the board is a non-conductor but metal tracks (usually of copper) are included to link the various components together. Reducing the size of computers involves reducing the width of the conducting tracks and thereby increasing their resistance. In practice energy losses due to track resistance are small compared with the losses in active components such as transistors and the integrated circuits (ICs or 'chips') that contain them.

True or False?

  1. The rate of heat loss in electrical conductors is proportional to the square of the electric current. true
  2. The clock frequency in a modern CPU is about 100 kHz. false
  3. The technique used in the fabrication of microprocessors is called lithography. true
  4. The distance between ‘components’ in an integrated circuit is typically about 750 nanometres. false
  5. The energy storage capacity of a laptop battery is about 1.5 kilowatt hours (kW h). false
  6. When a computer is turned off it uses less power than it does in stand-by mode. false
  7. The main source of heat loss in a laptop computer is the CPU. false
  8. The magnetic effect of an electric current was discovered by in 1820 by Hans Christian Ørsted (Oersted). true
  9. All metals show some resistance to electric current. true
  10. The power supply and the screen account for about 40% of the heat loss from a typical laptop computer. true