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Monday, June 18, 2001
On Hardware

The power of computers
Jasjot Singh Narula

FOR every electric and electronic gadget, performance is power and vice-versa. There are no two opinions about it. Even computer is merely an assembly of metal, plastic or silicon without power supply. Lifeless and unable to perform.

In fact, the power supply is the thrust that drives the equipment to perform. Without power supply, most of these would be lifeless, including computers.

There are so many components arranged in order to make a computer system. Each component contributes towards building a system. Normally computer users bargain for better drive, CD ROMs or even aesthetically designed cabinets. The buyer is more or less assured about the power supply in the average computer system, giving it little or no thought.

Computer power supply is a sealed metal box containing AC (Alternating Current) to DC (Direct Current) power conversion hardware. Power supply is always referred to as switching power supplies, uses switcher technology to convert the AC input to lower DC voltage. Typical voltages supplied are 12 volts, 5 volts, and 3.3 volts.


Twelve volt is used to run motor in disks drives and fans. Voltages of 3.3 volts and 5 volts are used only for digital circuits. Normally the power supply contains a button depicting 120 V and 220 V. Some countries outside India have 120 V of output. Most of the gadgets work at 220 V in India.

Power supply hardware is located on the corner of the cabinet of computer system. There are some holes for the ventilation of the air to cool the components. The power supply is visible from the back of many systems. Two sockets are available on the backside of the power supply one for monitor cable and other for power cable from where it takes the 220 V supply. On the other side there are a bunch colourful wires for different components of the computer system.

There are so many electrical devices around us that are built to use 220 Volts AC domestic power supply (for example, mixer and drilling machines). However, the computers are not designed to use 220 volts directly. They require a device that converts the supply into DC and divides the voltage to feed or distribute to other components.

During the early 80s, power supply was quite heavy and bulky. Heavy transistors and huge capacitors used to convert line voltage at 120V (220V) into 5V and 12V DC.

These days such components are smaller in size and lighter in weight. Two important components are transistors and capacitors. The transistors act as high-speed switches, using incoming power to charge several capacitors in the power supply. Capacitors are the devices used to store electricity. Also, in the process of charging, the capacitors and the transistors convert the AC power into DC, the type PC uses.

The capacitor provides output for the computer components. Electricity runs from the capacitors to the components they supply energy to.

The outlet of the power supply contains several colourful wires. They split into several sets of wires ending in plugs. One set of wire plugs into the motherboard of the computer and other to the different accessories of the computer system.

Power supply distributes the voltage to different components according to the needs. For example, the motor of the hard disk requires 12 Volts of electricity to run but the CPU needs only 5 Volts.

Once the power is supplied to all PC components, the computer runs a test called POST (Power on self test). This test shows that the PC has enough power to start.

There are two different power supplies available with the cabinets like AT and ATX, The computer industry has been using ATX-based power supply, of late, and now it is a norm. ATX is now an industry specification that means that the power supply has the physical characteristics to fit in a standard ATX cabinet and the electrical characteristics to work with ATX motherboard.