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How Motherboards Conduct a Symphony of Data

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In this excerpt from How Computers Work, 10th Edition, learn how motherboards work, including details on CPU, chipsets, and PCI-Express slots.
This chapter is from the book

This chapter is from the book

UNDER the big top of your computer—or the little top of your smartphone or tablet—the microprocessor (the central processing unit or CPU) is always the headliner. You don’t see ads or reviews raving that a new PC has “revolutionary 100-ohm resistors!” Flash drives and incredibly realistic displays have the top supporting roles, but when it comes to the components on the motherboard—the mother of all boards—the CPU steals the spotlight.

There are many good reasons for the CPU’s fame, but like all stars, it owes a lot to the little components—the circuit board supporting parts without which the central microprocessor would be only a cold slab of silicon. And conversely, without the CPU and other specialized processors to keep all the parts running in harmony, the motherboard would be an orchestra without a conductor. Its components wouldn’t be able to hear what other members are playing. Electronic messages meant for the CPU would crash into the chips and each other, moving so fast there would be no time to read their license plates. Other messages would arrive like dying murder victims at the ER, so weak they can only whisper their crucial clues in pulses so faint the microprocessor can’t understand them. Computing would become a cacophony.

The role of the motherboard was much smaller in the early days of PCs because it was basically a platform for the microprocessor. It was a transportation grid for conveying signals back and forth between the CPU and the parts the CPU controlled—disc controller cards, video cards, sound cards, input/output cards. Back then, nearly everything that made a PC a PC was handled by expansion cards, which was handy because you could easily update a single component as innovation and budget allowed. Today, almost any computer comes with sound, video, disk controllers, and an assortment of input/output options all on the motherboard. Increasingly, some of these functions are now built into the CPU as well, but even then your computer’s character is largely determined by the mother-board’s capability, and those capabilities are largely defined by the parts that populate it.

Once again, we’re in LEGO land. The components that support the motherboard are made up of similar smaller parts divided among themselves in various strengths and concentrations. So here, ladies and gentlemen, are the little parts that make it all possible.

  • Tiny canisters house the circuit board’s strong men—the resistors! Clad in metal and ceramics, wrapped with colored stripes, they clamp down on the wild, untamed electricity before it has the chance to burn up the rest of the components. They literally take the heat for the rest of the motherboard.

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  • Wrapped in ceramic casing and coats of plastic are the voracious, singing capacitors! They hum as they consume great quantities of electrical charge, holding it in so other components can have a steady supply or a sudden surge of electricity when they need it.

  • Scattered everywhere on the motherboard are those mysterious, miniature monoliths, the microchips! What the millions of transistors do inside them is known to only a few.

  • And connecting them all are stripes of copper and aluminum, circuit traces, that tie it all together so the individual players are a coordinated whole.

How a Motherboard Brings It All Together

Because all devices are on the same buses, they all receive the same signals on the data and control buses. The memory controller, expansion cards, and other input/output devices along the bus constantly monitor the command lines. When a signal appears on the write command line, for example, all the input/output devices recognize the command. The devices, alerted by the write command, turn their attention to the address lines. If the address specified on those lines is not the address used by a device, it ignores the signals sent on the data lines.

If the signals on the address lines match the address used by the adapter, the adapter accepts the data sent on the address lines and uses that data to complete the write command.

PCI-Express slots are best known for being paired with powerful graphics cards that push video, games, and so on to your computer’s display. They come in multiple sizes and are the do-all, fit-all slot for a variety of expansion board types, not just graphics. The shorter ones here are x1 PCI-E slots and are common to all PCI Express slots. To handle graphics and sound data faster, the PCI-E slot can be expanded to x4, x8, or, shown here, x16 slots, where the numbers represent multiples of the speed of an x1 PCI-E slot. Their ability to move data is indicated by the multiplier factor in their designations.

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