Power Supplies

The computer’s components would not be able to operate without power. The device in the
computer that provides this power is the power supply (Figure 1.36). A power supply converts
110 volt or 220 volt AC current into the DC voltages that a computer needs to operate. These
are +3.3 volts DC, +5 volts DC, –5 volts DC (ground), +12 volts DC, –12 volts DC (ground),
and +5 volts DC standby. The 3.3 volts DC and +5 volts DC standby voltages were first used
by ATX motherboards.
FIGURE 1 . 3 6 A power supply

Power supplies are rated in watts. A watt is a unit of power. The higher the number, the
more power the power supply (and thus your computer) can use. Most computers use power
supplies in the 250- to 500-watt range.
Classic power supplies used only three types of connectors to power the various devices
within the computer (Figure 1.37): floppy drive power connectors (Berg connectors), AT system
connectors (P8 and P9), and standard peripheral power connectors (Molex connectors).
Each has a different appearance and way of connecting to the device. In addition, each type
is used for a specific purpose. Newer systems have a variety of similar, replacement, and additional connectors.