3 ms·

I think you might be underestimating the importance of RAM proximity to the CPU. The speed of electricity over copper is listed as being 299,792,458 meters per

I think you might be underestimating the importance of RAM proximity to the CPU. The speed of electricity over copper is listed as being 299,792,458 meters per second. A meter is 39.3701 inches, so that would be 11,802,859,050 (11.8 billion) inches per second. Now imagine a CPU trying to send a round trip electrical signal 4 billion times per second over the the RAM, over the distance of two inches (a 4 inch round trip). That's literally 16 billion inches of distance that you are asking the electrical signal to cover in the space of a second, but we know that the electricity can only physically cover 11.8 billion inches in that second, so we would essentially have a bottleneck due to the physical restrictions of the speed of light. Now imagine if you could cut that distance down from inches to cm or even millimeters... This is the benefit of having everything together on an integrated chip.

wtallis 6y ago
Speed of light delay due to trace length really is not that important to DRAM. Adding ~6cm to the round-trip path would add about 0.3ns to DRAM latency, which is already over 30ns. So we're looking at less than 1% difference between on-package vs on the motherboard. This is a much less important concern than signal integrity and drive strength necessary to maintain bandwidth when moving DRAM further from the CPU. Your argument would be much closer to relevant if we were discussing SRAM caches.