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Does the RAM being closed to CPU actually matter? (lemmy.zip)

submitted 4 days ago* (last edited 4 days ago) by veloren23djk@lemmy.zip to c/askelectronics@discuss.tchncs.de

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My friend told me that macbooks have their RAMs behind the CPU (or something along those lines) and it got me wondering. Does the distance between CPU and memory really make that much difference? 🤔

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[–] dgriffith@aussie.zone 3 points 4 days ago* (last edited 4 days ago)

You can generally go with the rule of thumb of "one foot per nanosecond" for the speed of light. Signals rattle along data lines a little slower because they are contained on a circuit board and not in free space, so it's more like "150mm per nanosecond" is the metric equivalent of propagation delay. That sounds pretty fast - and it is! It's like 50-60 percent of the speed of light.

But your average 3GHz multi-core CPU is doing a half dozen instructions per nanosecond. That means if you have your RAM over here and your CPU over there on your motherboard, you're going to have wait a measurable, impactful, amount of time for data to go back and forth between the two.

So the mobile/Apple idea of sticking your RAM directly on top of your CPU has some merit.