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Re:5.5 mm in 1.25 nanoseconds by krupan on Thursday January 13, 2022 @12:14PM (#29923418)
In chips because of the layers of conductors and insulators you are actually charging a capacitor, not just sending a signal down a lone wire.
Re:5.5 mm in 1.25 nanoseconds by kens on Thursday January 13, 2022 @01:33PM (#29924645)
Yes, a long bus is like a resistor-capacitor delay circuit. You can speed it up by using a bigger driver for more current, but that takes up more space and adds its own delay. I expect that the bus in the Xbox is split in two, with a second driver in the middle. This makes the first half faster, but the second half of the bus probably takes another clock cycle, which would explain the observed behavior.
Re:5.5 mm in 1.25 nanoseconds by AshamedCaptain on Thursday January 13, 2022 @12:22PM (#29923568)
That's how all conductors work, not just "in chips due to layers of conductors and insulators". The thing is that in most situations you just model the conductor away as a "perfect ideal wire" and everything usually just works since you don't care about these small delays and/or you have very high power. But when you enter sub-nanosecond and/or sub-mW territory...
Re:5.5 mm in 1.25 nanoseconds by tom-thistime on Thursday January 13, 2022 @02:01PM (#29925089)
You're always driving a waveguide that has inductance and capacitance per unit length. But when resistance is high enough you are just charging a big distributed capacitor. It's a different regime from the high-conductivity situation (which looks like a transmission line). Either picture could apply at sub-ns speeds, it depends mainly on the resistance.
Re:5.5 mm in 1.25 nanoseconds by jhgb on Thursday January 13, 2022 @01:31PM (#29924619)
But IC interconnects have a very small cross section, so for them this problem is much more pressing.