[kamilner]

Why is it that LPDDR is recently faster than DDR of the same 'generation'? I thought LPDDR is purely a lower voltage version of DDR, so I naively would have expected worse performance. Is it because it's typically closer (physically) to the CPU?

[sliken]

I believe it's just the advantages you get from very short trace lengths. Dimm slots are usually inches away, so you end up with long traces from CPU -> dimm slot, pay the overhead of the dimm slot connection, and then traces within a dimm.

LPDDR on the other hand move the individual dimm chips as close as possible to the CPU and don't have any connector. This also makes it much easier to have wider memory. A 13" MBP can have a 512 bit wide memory system with at least 16 channels in a thin/light laptop that is quite power efficient. To get similar with DIMMs you'd have to buy a dual socket server motherboard with 8 channels per socket and would be lucky to fit that in an ATX size motherboard in a 1.75" thick chassis.

[bcrl]

DDR is typically a bus with more than 1 DIMM slot per channel. LPDDR is typically point to point. Electrically, it's a lot easier to meet signal integrity requirements on a point to point trace than it is to make a multi drop bus work properly.

[ksec]

>I thought LPDDR is purely a lower voltage version of DDR

The only similarity between LPDDR5 and DDR5 is its name. Otherwise you could think of them as completely different technology just like HBM and DDR.

[wtallis]

DDR4L is the low-voltage version of DDR4. LPDDR4(x) are very different, and have at least as much in common with GDDRx as they do with desktop DDR standards.

[dhdc]

More importantly, because of the low-power requirement, LPDDR typically have better binned dies than DDR.

[grue_some]

LPDDR uses a wider bus so, at a similar clock rate, it is faster.