How CPUs work: A closer look at exterior processor design

It's what's inside that counts, but the exterior design of computer processors is pretty important, too.

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Credit: Thomas Ryan
What's outside counts, too

Processors are at the heart of your computer. CPUs process millions of instructions every second so you can watch Netflix and play Fallout 4. CPUs throttle their clockspeeds to save power, and boost them to help you open a new tab in Chrome. But have you had a chance to take a good look at one—a really good look?

As the recent Skylake CPU-crushing debacle has demonstrated, the physical characteristics of a chip are more important than you might think. Let’s take a deeper look at the Intel Core i7-4790K and AMD FX-8370.

(Looking for information on how to actually install a processor? This CPU installation guide can help. And for a deep-level explanation of chip design—logic units, instruction cycles, etc.—check out Wikipedia’s deeply detailed CPU page)

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Credit: Thomas Ryan
Mind the triangle

As anybody who has ever built a PC can tell you, securing a CPU in its socket can be a harrowing experience if it’s your first time. To ensure that your new Intel CPU is placed correctly in your motherboard's socket, line up the gold triangle on the corner of your chip with the complementary triangle on the edge of the socket.

This tiny little triangle can be a lifesaver. But inevitably, it’ll still feel like you’re pushing too hard on the lever when you’re latching down the processor. You’re not.

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Credit: Thomas Ryan
Contact patches

There are hundreds of small electrical contact points on the underside of modern Intel CPUs. Each one is pressed atop a small pin that’s part of the Land Grid Array in the socket so the CPU can get power from the motherboard and communicate with the rest of the system.

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Credit: Thomas Ryan
Level up

The metal heat spreader and small PCB that make up the external features of an Intel CPU are terraced slightly. That’s done to separate two distinct resting areas on the CPU: the retention bracket that holds the CPU into the socket, and the heatsink that sits on top of the CPU’s heat spreader. Specifically, the socket retention bracket sits on top of the middle tier made of metal, while the heatsink sits on the top tier. That way, the two don’t touch.

There is also a small notch here that works with a symetical notch on the other side of the chip as well as the gold triangle we covered earlier to help you place the CPU in its socket correctly.

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Credit: Thomas Ryan
Test pads

On the upper edge of Intel’s CPUs you can see contact patches that look similar to contact points on the bottom of the chip. These are test pads used during the bring-up and debugging process that Intel’s CPUs go through. They’re also used to help test and bin CPUs at Intel’s factory before they are sent to customers. Intel’s testing process verifies that a chip is working correctly, while the binning process determines what clock speed the chip will operate at within its particular model classification.

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Credit: Thomas Ryan
The underside

In addition to the contact pads on the underside of an Intel CPU, there’s also a slate of power delivery circuits, including some capacitors—the structures in the center of the chip. This Intel Core i7-4790K packs more capacitors than the i7-4770K for smoother power delivery during overclocking attempts.

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Credit: Thomas Ryan
The other side

Moving over to AMD’s CPUs, we can see that there are no contact pads or power delivery circuitry on the underside. Instead, there’s a grid of small pins that allow the CPU to connect to the motherboard electrically. That’s because Intel’s LGA design places the pins in the motherboard socket, but AMD’s Pin Grid Array design features pins on the processor itself.

This particular chip, the AMD FX-8370, uses AMD’s socket AM3+ and has over 900 hundred pins on its underside.

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Credit: Thomas Ryan
Pins and more pins

The other thing to notice here is just how dense the pins are on AMD’s CPUs. Intel’s chips can be safely set down just about anywhere, but handling AMD’s chips requires much more care—one klutzy move can easily mean a bent pin or two. Luckily, bent pins can often be fixed by using a credit card to bend the pins back into their proper position.

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Credit: Thomas Ryan
Keep it on the level

There’s no socket retention bracket to hold AMD’s CPUs in place on the motherboard, so they also lack one of the terraced steps found on Intel chips. AMD places a small lever on the edge of the motherboard socket that uses the pins on the bottom of the CPU to lock it into place and prevent unwanted movement.

The base of the heatsink sits on top of the large flat heat spreader that covers CPU’s silicon die.

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Credit: Thomas Ryan
Mind the triangle redux

But AMD and Intel processors aren’t complete opposites. AMD’s chips also include a small triangle marker that helps you orient the CPU in the motherboard socket. This little triangle can be found on both the top and bottom sides of the chip, and there’s a complementary marker on every AMD motherboard.

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Under the hood...er, heat spreader

Another thing that both Intel and AMD have in common is the silicon die sitting inside the processor, at the center of the CPU packaging that we’ve just looked at. (Pictured: a wafer of many, many Intel Haswell chip dies.)

These tiny integrated circuits are about the same length as a sewing pin and enable your computer to calculate the pathfinding for enemy players in a game or to display a Twitch stream of your friend making a sandwich. Whatever you use your PC for, the technology behind it is borderline magical—and the processor’s the brains behind a lot of it.

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Credit: Thomas Ryan
But wait, there's more!

Interested in more deep-dives into the hardware powering your PC? We’ve also chopped up RAM and torn apart a motherboard to show you how they work. Check them out!