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The Case and Power Supply
By: McGraw-Hill/Osborne
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    Table of Contents:
  • The Case and Power Supply
  • The Chassis
  • Expansion
  • Other Considerations
  • With or Without a Power Supply?
  • Anatomy of an ATX Power Supply
  • Power Supply Connectors
  • Choosing a Power Supply
  • Surge Protector

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    The Case and Power Supply - Power Supply Connectors

    (Page 7 of 9 )

    Most ATX power supplies feature five types of connectors. They include connectors to provide power and auxiliary power to the motherboard, and power to the internal peripherals such as the hard drive, optical drives, and floppy drive. Even some video cards need power from the power supply.

    Each of these female connectors has a specific range of pinouts, mostly consisting of +12V, +5V, and ground pins. Most were also designed by a company called Molex, and although Molex doesn’t have a true monopoly on the power connectors within a PC, it’s considerably dominant. We’ll focus our attention on Molex connectors, since they’re by far the most common. Figure 1-8 shows the primary power connector for an ATX motherboard. It’s keyed in such a way that you can’t connect it backward or otherwise erroneously. It provides plenty of 12V, 5V, and 3.3V lines, as well as the Power_Good connector and several ground wires. Athlon-based systems currently require only this connector to run everything on the motherboard, including the processor and all of the core logic.


    Figure 1-8 The 20-pin main ATX motherboard power supply connector (Molex 39-01-2200)

    Included with standard version 2.03 specification power supplies, the 12V connector is used chiefly by modern Pentium 4 motherboards (see Figure 1-9). The voltage requirements of the processor exceed the voltage provided by the main 20-pin connector, and thus this connector, which consists of two 12V leads and two grounds, is used to allow the system to draw the extra current required. It’s similarly keyed to prevent an incorrect connection.


    Figure 1-9 ATX 12V connector (required for some Pentium 4 motherboards) (Molex 39-01-2040)


    Some motherboards bypass the 12V connector by providing standard sockets for Molex 15-24-4048 connectors. This is a boon for people with an older power supply lacking a 12V connector who wish to upgrade to a Pentium 4 motherboard and processor. If you buy your power supply new, however, make sure it has the extra 12V lead; chances are, it will.

    When memory was changed to draw 3.3V, its draw to maintain sufficient amperage became greater. Although rarely used, the auxiliary connector shown in Figure 1-10 was added to the power supply specification of 250W or greater power supplies to supply the extra current. If your motherboard doesn’t have a receptacle for this power connector, simply ignore it.


    Figure 1-10  ATX auxiliary power connector (Molex 8993)


    Figure 1-11  A peripheral power connector (Molex 15-24-4048)


    Figure 1-12 A peripheral connector Y-splitter

    In the snake’s nest of wires that billows out of the power supply, the peripheral power connector (Figure 1-11) is the most common connector that you’ll find. The peripheral connectors are used to power most of the interior devices in the system. Even if you run short of peripheral connectors, you can use a Y-splitter (Figure 1-12), available at any good computer store, to add more connectors.

    Smaller peripheral connectors (Figure 1-13) are far less common than the larger ones. Most power supplies have only one or two of these, and they’re most commonly used for powering the floppy drive, although some other small drives such as SuperDisk (LS-120) drives also use them.


    Figure 1-13  A floppy power connector (Molex 22-01-1044)

    This chapter is from Build Your Own High Performance Gamers' Mod PC, by Chen and Durham (McGraw-Hill/Osborne, 2004, ISBN: 0072229012). Check it out at your favorite bookstore today. Buy this book now.

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