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 lie at the heart of your computer. They juggle millions of instructions every second so you can watch Netflix and play Fallout 4. They throttle their clockspeeds to save power, and boost them to help you open a new tab in Chrome. But have you actually taken a good look at a processor—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 closely examine Intel's Core i7-4790K and AMD's FX-8370.

(For information on how to actually install a processor, check out this CPU installation guide. We also recommend this deep-level explanation of chip design—logic units, instruction cycles, etc.—on Wikipedia.)

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Credit: Thomas Ryan
Mind the triangle

Anyone who's built a PC can tell you that securing a CPU in its socket can be a harrowing experience—especially if it’s your first time. Here's the trick for Intel (and AMD) CPUs: Line up the gold triangle on the corner of your chip with the complementary triangle on the edge of the socket.

Even with the triangle to guide you, it will 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

Hundreds of small electrical contact points dot 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 make up the external features of an Intel CPU. You'll see they are terraced slightly to create two distinct resting areas on the CPU. The load plate, which holds the CPU in the socket, sits on the middle tier. The heatsink sits on the top tier, the CPU's heat spreader. That way, the two don’t touch.

A small notch here, as well as a symmetrical notch on the other side, and the aforementioned triangle, all help you place the CPU in its socket.

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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 the contact points on the bottom of the chip. These are test pads used during the CPU's bring-up and debugging process. They’re also used to help test and bin Intel's CPUs at the factory before they're 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 AMD difference

On AMD’s CPUs, note the absence of contact pads or power delivery circuitry on the underside. While Intel's LGA design places the pins in the motherboard socket, AMD’s Pin Grid Array design features a dense grid of pins that connects the CPU to the motherboard elecrtically.

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

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Credit: Thomas Ryan
Pins and more pins

Because the pins on an AMD CPU are exposed on the chip's underside, one klutzy move can easily mean a bent pin or two. (In contrast, Intel's CPUs can be set down just about anywhere without risk). 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 load plate to hold AMD’s CPUs in place on the motherboard, so they lack one of the terraced steps found on Intel chips. Instead, a small lever at the edge of an AMD motherboard socket initiates tension around the pins on the bottom of the CPU to lock it in place.

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

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Credit: Thomas Ryan
Mind the triangle redux

AMD and Intel processors have one key feature in common. 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 CPUs share is the silicon die sitting inside the processor, at the center of the CPU packaging we just saw. (Pictured: a wafer of many, many Intel Haswell chip dies.)

These tiny integrated circuits are about the same length as a 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.

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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!