Computer Beginner Guide

Industry standard PC, XT, AT, Baby-AT, and LPX motherboards all use the same type of main power supply connectors. AT power supplies feature two main power connectors (P8 and P9), each with six pins that attach the power supply to the motherboard. These are rated at 5 amps per pin, at up to 250V. These two connectors are shown in Figure below. All standard PC power supplies that use the P8 and P9 connectors have them installed end to end so that the two black wires (ground connections) on both power cables are next to each other. Note the designations "P8" and "P9" are not fully standardized, although most use those designations because that is what IBM stamped on the originals. Some power supplies have them labeled as P1/P2 instead. Because these connectors usually have a clasp that prevents them from being inserted backward on the motherboard's pins, the major concern is getting the two connectors in the correct orientation side by side and also

As motherboards and processors evolved, the need for power became greater. In particular, chipsets and DIMMs were designed to run on 3.3V, increasing the current demand at that voltage. In addition, most boards included CPU voltage regulators that were designed to convert +5V power into the unique voltage levels required by the processors the board supported. Eventually, the high current demands on the +3.3V and +5V outputs were proving too much for the design of the connectors and terminals. Each of the terminals in the main power connector are rated for 6 amps (A), which allows for a maximum draw of 18A of +3.3V power and 24A of +5V power. These maximums match the ratings of an approximately 250-watt-rated power supply. Because motherboards with high-speed processors and multiple cards installed could draw more power than that and power supply manufacturers were building supplies with 300-watt and higher ratings, melted connectors were becoming more and more common. The

Power for the processor comes from a device called the voltage regulator module (VRM), which is built in to most modern motherboards. This device senses the CPU voltage requirements (usually via sense pins on the processor) and calibrates itself to provide the proper voltage to run the CPU. The design of a VRM enables it to run on either 5V or 12V for input power. Most have used 5V over the years, but many are now converting to 12V because of the lower current requirements at that voltage. In addition, other devices might have already loaded the 5V, whereas, typically, only drive motors use the 12V. Whether the VRM on your board uses 5V or 12V depends on the particular motherboard or regulator design. Many modern voltage regulator ICs are designed to run on anything from a 4V to a 36V input, so it is up to the motherboard designer as to how they will be configured. For example, I studied a system using an FIC (First International Computer) SD-11 motherboard, which used a

Three main types of power switches are used on PCs. They can be described as follows: Integral Power Supply AC switch Front Panel Power Supply AC switch Front Panel Motherboard Controlled switch The earliest systems had power switches integrated or built directly into the power supply, which turned the main AC power to the system on and off. This was a simple design, but because the power supply was mounted to the rear or side of the system, it required reaching around to the back to actuate the switch. Also, switching the AC power directly meant the system couldn't be remotely started without special hardware. Starting in the late '80s, systems began using remote front panel switches. These were essentially the same power supply design as the first type. The only difference was that the AC switch was now mounted remotely (usually on the front panel of the chassis), rather than integrated in the power supply unit. The switch was connected to the power supp

PC power supplies are of a switching rather than a linear design. The switching type of design uses a high-speed oscillator circuit to convert the higher wall-socket AC voltage to the much lower DC voltage used to power the PC and PC components. Switching-type power supplies are noted for being very efficient in size, weight, and energy in comparison to the linear design, which uses a large internal transformer to generate various outputs. This type of transformer-based design is inefficient in at least three ways. First, the output voltage of the transformer linearly follows the input voltage (hence the name linear ), so any fluctuations in the AC power going into the system can cause problems with the output. Second, the high current-level (power) requirements of a PC system require the use of heavy wiring in the transformer. Third, the 60Hz frequency of the AC power supplied from your building is difficult to filter out inside the power supply, requiring large and e

In addition to power output, many other specifications and features go into making a high-quality power supply. High-quality power supplies also help protect your systems. A high quality power supply from a vendor such as PC Power and Cooling will not be damaged if any of the following conditions occur: A 100% power outage of any duration A brownout of any kind A spike of up to 2,500V applied directly to the AC input (for example, a lightning strike or a lightning simulation test) Decent power supplies have an extremely low current leakage to ground of less than 500 microamps. This safety feature is important if your outlet has a missing or an improperly wired ground line. As you can see, these specifications are fairly tough and are certainly representative of a high-quality power supply. Make sure that your supply can meet these specifications. You can also use many other criteria to evaluate a power supply. The power supply is a component many users ignore whe

Recently, the power line efficiency and harmonic distortion generation of PC power supplies has come under examination. This generally falls under the topic of the power factor of the supply. Interest in power factor is not only due to an improvement in power efficiency, but also because of a reduction in the generation of harmonics back on the power line. In particular, new standards are now mandatory in many European Union (EU) countries that require harmonics be reduced below a specific amount. The circuitry required to do this is called power factor correction (PFC). The power factor measures how effectively electrical power is being used and is expressed as a number between 0 and 1. A high power factor means that electrical power is being used effectively, whereas a low power factor indicates poor utilization of electrical power. To understand the power factor, you must understand how power is used. Generally, two types of loads are placed on AC power lines: Resi

As the standard PC configuration has grown to include capabilities formerly considered options, the power requirements of the system have increased steadily. Larger displays, CD-ROM drives, and audio adapters all need more power to run, and the cost of operating a PC rises steadily. To address these concerns, several programs and standards are now being developed that are intended to reduce the power needed to run a PC as much as possible. For standard desktop systems, power management is a matter of economy and convenience. By turning off specific components of the PC when they are not in use, you can reduce the electric bill and avoid having to power the computer up and down manually. For portable systems, power management is far more important. Adding CD-ROMs, speakers, and other components to a laptop or notebook computer reduces even further what is in many cases a short battery life. By adding new power management technology, a portable system can supply power only

Troubleshooting the power supply basically means isolating the supply as the cause of problems within a system and, if necessary, replacing it. Many symptoms lead to suspect that the power supply in a system is failing. This can sometimes be difficult for an inexperienced technician to see because at times little connection seems to exist between the symptom and the cause—the power supply. For example, in many cases a parity check error message can indicate a problem with the power supply. This might seem strange because the parity check message specifically refers to memory that has failed. The connection is that the power supply powers the memory, and memory with inadequate power fails. It takes some experience to know when this type of failure is power related and not caused by the memory. One clue is the repeatability of the problem. If the parity check message (or other problem) appears frequently and identifies the same memory location each time, I would suspect tha

Some of the available replacement power supplies have higher-capacity cooling fans than the originals, which can greatly prolong system life and minimize overheating problems—especially for the newer, hotter-running processors. If system noise is a problem, models with special fans can run more quietly than the standard models. These power supplies often use larger-diameter fans that spin more slowly, so they run more quietly but move the same amount of air as the smaller fans. PC Power and Cooling specializes in heavy-duty and quiet supplies. Ventilation in a system is also important. You must ensure adequate airflow to cool the hotter items in the system. Many systems today (especially those from larger vendors such as Dell, Gateway, MPC, and so on) still use passive heatsinks that require a steady stream of air to cool the chip. If the processor heatsink has its own fan, this is not much of a concern. If you have free expansion slots, you should space out the boards in

One simple test you can perform on a power supply is to check the output voltages. This shows whether a power supply is operating correctly and whether the output voltages are within the correct tolerance range. Note that you must measure all voltages with the power supply connected to a proper load, which usually means testing while the power supply is still installed in the system and connected to the motherboard and peripheral devices. Selecting a Meter You need a simple digital multimeter (DMM) or digital volt-ohm meter (DVOM) to perform voltage and resistance checks on electronic circuits. You should use only a DMM instead of the older needle-type multimeters because the older meters work by injecting 9V into the circuit when measuring resistance, which damages most computer circuits. A DMM uses a much smaller voltage (usually 1.5V) when making resistance measurements, which is safe for electronic equipment. You can get a good DMM with many features from several so

You can use several types of specialized test gear to test power supplies more effectively. Because the power supply is one of the most failure-prone items in PCs today, you should have these specialized items if you service many PC systems. One of the greatest additions to your toolbox is a digital infrared thermometer. They also are called noncontact thermometers because they measure by sensing infrared energy without having to touch the item they are reading. This enables me to make instant spot checks of the temperature of a chip, a board, or the system chassis. They are available from companies such as Raytek for under $100. To use these handheld items, you point at an object and then pull the trigger. Within seconds, the display shows a temperature readout accurate to +/–3°F (2°C). These devices are invaluable in checking to ensure the components in your system are adequately cooled. Variable Voltage Transformer When testing power supplies, it is sometimes desirabl

The components of a PC system are mounted within a chassis or case. The main feature you must first decide on is which form factor the case needs to be. Several somewhat standardized form factors are available for PC chassis, including: Slimline Desktop Desktop Mini-Tower Mid-Tower Full Tower (Server) Large Server Rackmount The Slimline chassis are typically used with NLX form factor boards that are a riser card design. Recently, an addendum to the ATX form factor was created that enables riser cards to be used, allowing ATX boards to be used even in Slimline systems. In addition to the case form factor, the following are several other things you should consider before purchasing your case: Motherboard form factor supported . A given chassis usually accepts one or more standard motherboard form factors. Most of the chassis accept ATX (or Micro-ATX or Flex-ATX) form factor motherboards, whereas some accept Baby-AT form factor motherboards as well

Power-protection systems do just what the name implies: They protect your equipment from the effects of power surges and power failures. In particular, power surges and spikes can damage computer equipment, and a loss of power can result in lost data. Before considering any further levels of power protection, you should know that a quality power supply already affords you a substantial amount of protection. High-end power supplies from the vendors I recommend are designed to provide protection from higher-than-normal voltages and currents, and they provide a limited amount of power-line noise filtering. Some of the inexpensive aftermarket power supplies probably do not have this sort of protection. If you have an inexpensive computer, further protecting your system might be wise. Of course, the easiest form of protection is to turn off and unplug your computer equipment (including your modem) when a thunderstorm is imminent. However, when this is not possible, other alte

The next level of power protection includes backup power-protection devices. These units can provide power in case of a complete blackout, thereby providing the time necessary for an orderly system shutdown. Two types are available: the standby power supply ( SPS ) and the uninterruptible power supply ( UPS ). The UPS is a special device because it does much more than just provide backup power—it is also the best kind of line conditioner you can buy. Standby Power Supplies A standby power supply is known as an offline device: It functions only when normal power is disrupted. An SPS system uses a special circuit that can sense the AC line current. If the sensor detects a loss of power on the line, the system quickly switches over to a standby battery and power inverter. The power inverter converts the battery power to 120V AC power, which is then supplied to the system. SPS systems do work, but sometimes a problem occurs during the switch to battery power. If the switch i

All 16-bit and higher systems have a special type of chip in them that combines a real-time clock (RTC) with at least 64 bytes (including the clock data) of nonvolatile RAM (NVRAM) memory. This chip is officially called the RTC/NVRAM chip, but it is often referred to as the CMOS or CMOS RAM chip because the type of chip used is produced using a CMOS (complementary metal-oxide semiconductor) process. CMOS design chips are known for very low power consumption. This special RTC/NVRAM chip is designed to run off a battery for several years. The original chip of this type used in the IBM AT was the Motorola MC146818 chip. Although the chips used today have different manufacturers and part numbers, they all are designed to be compatible with this original Motorola part. Most modern motherboards have the RTC/NVRAM built in to the motherboard chipset South Bridge or I/O Controller Hub (ICH) component. The function of the real-time clock should be obvious: The clock enables softwa

In these days of commodity parts and component pricing, building your own system from scratch is no longer the daunting process it once was. Every component necessary to build a PC system is available off the shelf at competitive pricing. In many cases, the system you build can use the same or even better components than the top name-brand systems. There are, however, some cautions to heed. The main thing to note is that you rarely save money when building your own system; purchasing a complete system from a mail-order vendor or mass merchandiser is almost always less expensive. The reason for this is simple: Most system vendors who build systems to order use many, if not all, of the same components you can use when building your own system. The difference is that they buy these components in quantity and receive a much larger discount than you can by purchasing only one of a particular item. In addition, you pay only one shipping and handling charge when you purchase a