I've noticed pictures of decaped IC chips and noticed that CPU (cores) found on die are all located close together. Is there a reason for this or is it just a coincidence? If it is not a coincidence then can someone provide a detail explanation please as to why? The application could be any model Intel CPU for the desktop market. But really any application that contains multi cores.
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\$\begingroup\$ What chips are you referring to? \$\endgroup\$– KartmanDec 28, 2021 at 20:25
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\$\begingroup\$ @kartman. Any Intel CPU for the desktop market. \$\endgroup\$– JoeTDec 28, 2021 at 20:32
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3\$\begingroup\$ Die space is expensive, the larger the die the higher the defect rate. So everything is squished together as tight as possible. But I don't think I really understand your question. What else would you put between the cores? \$\endgroup\$– MatDec 28, 2021 at 20:34
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\$\begingroup\$ But not all of them have multiple cores. What pictures have you noticed? \$\endgroup\$– KartmanDec 28, 2021 at 20:34
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\$\begingroup\$ Even the tiny added parasitic inductance and capacitance from increased distance by a few mm is something to pay serious attention to from both switching losses and delay point of view. \$\endgroup\$– winnyDec 28, 2021 at 21:06
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2 Answers
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I assume you're talking about a multi-core processor such as this one from Intel (source):
As is kind of evident from the picture, the CPU cores themselves have common logic that they all need access to. Such a component that pretty much all modern processors have is a level-3 (L3) cache ("Last Level Cache"/LLC in the picture). These connections need to be as short as possible to reduce delays, allowing for higher clock speeds (electrical signals travel at a finite speed, which makes the signal propagation delay proportional to the wire length). Because all other parts, such as graphics, memory interfaces, display controllers, ..., are also hierarchically grouped for the same reason, this leaves the cores bunched together.
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2\$\begingroup\$ Please add a link or citation for the image you copied into your answer. The policy for this site is that copied material must be attributed to the original source. \$\endgroup\$ Dec 28, 2021 at 20:51
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\$\begingroup\$ @ElliotAlderson Ok, I'm sorry. I did not realize that the image would be copied to imgur automatically. \$\endgroup\$ Dec 28, 2021 at 20:56
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\$\begingroup\$ @MaxKlein yes I was referring to a multi core processor. \$\endgroup\$– JoeTDec 29, 2021 at 0:40
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CPU cores have high trace count buses connecting them and their shared caches. They're physically arranged close to each other to keep those costly and power-hungry buses as short as possible. Distributing the cores widely across the die would make routing all of those connections harder while possibly making communication less efficient.
answered Dec 28, 2021 at 20:40