In personal computer, the power supply unit is a metal box usually found in a corner of the System Unit (Fig.I-32). This box is known as SMPS (Switch Mode Power Supply) box. Visible from the back of the System Unit, the power supply box contains the power-cord receptacle and a cooling fan. Power supply, often referred to as 'switching power supply'. uses switcher technology to convert the AC current into DC current. Once the current is converte~ to DC, the power supply unit sends the required wattage to different components of the computer like monitor, hard disk, CD-ROM, floppy disk drive etc. The measurement unit of voltage is watts.