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by brennanpeterson 785 days ago
Half your wires deliver power, half deliver signal. So if you do both on the same side, you need twice the density of wires. If you split the delivery into two parts, you get double the density without needing to make things smaller.
1 comments
blagie 785 days ago
This isn't quite right. Big wires (ideally entire planes) deliver power. Small wires deliver signal. Half and half isn't the right split, and you don't want to make power wires smaller.

The very different requirements of the two is where a lot of the gains come in.

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mbajkowski 785 days ago
It is going to get even a bit more interesting when you consider power gaters and virtual power supplies. Now the real power will be on the back side and the virtual power will be on the front side. Fun time for power analysis.
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brennanpeterson 784 days ago
True! I went a little far in the name of 'eli5'. I think it roughly holds that you gain about a factor of 1.5 in routing density by removing the power distribution, so you can relax some critical patterning. But I havent looked closely in a long time.
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blagie 783 days ago
Oft-missed pedagogical point for working with five-year-olds:

Precision is important. You'll notice every comment I made was as simple as I can make it, but /technically correct/. I did not oversimplify to where I changed facts.

* It's okay if five-year-olds don't fully understand something. That builds exposure, and leaves a placeholder for future information and curiosity.

* On the other hand, if you build out an array of misconceptions, those become very expensive to address later.

To a large extent, the younger the child, the more comfortable they will be with being told things they don't understand. A baby doesn't care if you're reading them a book on trucks or a book on homeomorphic transformations; they're picking out the phonemes. A toddler will trust you as an adult, and won't understand 90% of the stuff they hear anyways. A five-year-old, you can still say a lot they won't understand and they'll be not just okay but happy. By maybe seven, lack-of-understanding will become frustrating, and in most cases, by eleven, it's gone.

I could write a long essay on this stuff, and why it's so important to maintain that ability to be confused and half-understand, but I very intentionally leave placeholders when working with five-year-olds.

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