Linux+: Hardware Part 05 – Power Supply Being a computer, none of the components can work without electricity. The need for power makes the power supply a crucial component. Without it, nothing works. If it fails, the system powers down and application data can be lost. In the U.S., the power coming out of a standard outlet is 120 volts at 60 Hz. Voltages and wavelengths differ in other countries, but the power supply in a computer manages the same task; it converts the incoming Alternating Current (AC) to Direct Current (DC). The DC power needed by internal components is usually one of three voltages: 3.3 volts, 5 volts or 12 volts (some of these may be positive or negative). NOTE: Be aware that some power supplies have a switch on the back to change the input voltage from the wall outlet. Be aware that this voltage must be set correctly or the power supply will not work. If the voltage switch is set higher than the incoming voltage the system will do nothing. The system, when powered on, will appear as if it has a faulty power supply. Some power supplies not have a switch and can auto-sense the incoming power level and adjust itself accordingly. If the switch is set too low, such as 120 volts, and the incoming voltage is 230 volts, the system can be damaged. Every component within the system uses a power connector from the power supply. For example, a hard disk, tape drive, CD/DVD-ROM, etc. will all require a connector to supply power. Each device has a specific power consumption which is rated in watts. All of the devices connected to the power supply will require a set amount of watts to operate. If the wattage consumption is higher than the rating of the power supply, the power supply can shut off before it is overloaded and causes system damage. When adding devices to a system, be aware of the current and new wattage usage as well as the wattage capacity of the power supply. Do not let the wattage usage exceed the wattage supplied by the power supply. You should also be aware that some motherboards require a specific power connector to supply power to the motherboard. When a power supply is replaced it may need to be the same type. If a motherboard is switched, a specific power supply may need to be installed to connect to the motherboard. NOTE: Power usage also can increase with expansion cards. If a video expansion card is used instead of an onboard video processor, the power consumption can increase. Multi-processors can also increase power requirements as well as an increase in RAM. Be aware that to prevent a power loss when all power goes out (blackout) or the power is reduced enough to dim lights (brownout) which can cause a computer to power off, there are ways to prevent this from happening. Uninterruptible Power Supplies (UPS) can be used to supply power from batteries. A UPS is plugged into the wall outlet and is continuously charging its batteries. While the charging is occurring, the computer is plugged into the UPS and is running off the batteries. If the power should fail, the system runs off the batteries as they quit charging. When power is restored, the batteries start charging again. The UPS is connected to the system with a cable of some type, usually Universal Serial Bus (USB), which can alert the system that the power is off. When the battery level reaches a specified point of discharge, the system will power itself off by performing a proper shutdown so as not to corrupt data. If needed, a user can save data, close all applications and power the computer off before the batteries discharge too much. The power supply also provides another important function for the computer. Power supplies have a built-in fan to help cool the internal components of the system. Devices and components within a computer all heat up. If the temperature reaches a specific level, devices and components can fail from being overheated. The cases are ventilated to allow air in or out. The fan within the power supply can blow air into the case, or suck it out. For larger systems, which may contain more devices and components, multiple fans other than that in the power supply can be used. NOTE: Systems can have positive (more) or negative (less) air pressure for cooling. For positive pressure, more air is pumped into the system than is being exhausted. For negative pressure, more air is exhausted than pumped in. With a positive pressure system, there is more dust collected inside to clean out. With negative pressure systems, there is less air for internal fans to use to cool internal devices such as the CPU (still some dust though). No matter which you use, air filters are good to use to prevent dust anyway. Another subject dealing with power is Power Management. All computer systems, mobile ones especially, rely on Power Management to conserve power. Notebooks require the power to be managed to help extend the battery life. Desktop systems can extend UPS up-time by powering down components which are not used to conserve the UPS battery. Power Management allows a system to power off devices which are not being used. Most people notice monitors which turn off after a specified time of no mouse or keyboard activity. Originally, the first component to offer Power Management were processors. When the system was idle and there was no data to process, the CPU would power off and wait for system activity. Later, hard disks could also be powered off when inactive. Advanced Power Management (APM) and Advanced Configuration and Power Interface (ACPI) were later introduced which allowed other components and devices to power off or reduce power for energy conservation. APM and ACPI settings were made in the BIOS configuration. ACPI also include monitoring the internal temperature of a system to power it off if the system started to overheat. ACPI also allowed the power button to place the system in a hibernate state instead of powering off and on. Another function of ACPI is to “wake up” a hibernating system when a fax modem receives a call or a network card receives a specific packet.