4 ms·

> On most x86 cores the limit is around 6 GB/s and about 20 GB/s for Apple M chips. What makes M-series have 3x the bandwidth (per core), over x86?

by tiffanyh 10mo ago

MindSpunk 10mo ago
M-series have a substantially wider memory bus allowing much higher throughput. It's not really an x86/M-series thing, rather it's a packaging limitation. Apple integrates the memory into the same package as the CPU, the vast majority of x86 CPUs are socketed with socketed memory. Apple are able to push a wider bus at higher frequencies because they aren't limited by signal integrity problems you encounter trying to do the same over sockets and motherboard traces. x86 CPUs like the Ryzen AI Max 395+, when packaged without socketed memory, are able to push equally wide busses at high frequencies.
Analemma_ 10mo ago
The sibling comment has the correct, more detailed answer, but the high-level answer is that the M-series chips are SoCs with all the RAM on-die. That lets you push way more data than you can over a bus out to socketed memory. The tradeoff is that it's non-upgradeable, but (contra some people who claim this is only a cash-grab by Apple to prevent RAM upgrades) it's worth it for the bandwidth.
- Scaevolus 10mo ago
  Apple had soldered DDR ram for a long time that was no faster than any other laptop. It's only with the Apple Silicon M1 that it started being notably higher bandwidth.
  - vlovich123 10mo ago
    There were always technical benefits like lower power consumption iirc
- eru 10mo ago
  > The tradeoff is that it's non-upgradeable, but (contra some people who claim this is only a cash-grab by Apple to prevent RAM upgrades) it's worth it for the bandwidth. That, and if you come at it from the phone / tablet or even laptop angle: most people are quite ok just buying their computing devices pre-assembled and not worrying about upgrading them. You just buy a new one when the old one fails or you want an upgrade. Similar to how cars these days are harder to repair for the layman, but they also need much less maintenance. The guy who was always tinkering away with his car in old American sitcoms wasn't just a trope, he was truth-in-television. Approximately no one has to do that anymore with modern cars.
- fanf2 10mo ago
  It isn’t on-die, the ram is separate chips in the same package. See the pics about halfway down https://www.apple.com/de/newsroom/2023/10/apple-unveils-m3-m3-pro-and-m3-max-the-most-advanced-chips-for-a-personal-computer/ https://www.apple.com/de/newsroom/2023/10/apple-unveils-m3-m...
- 15155 10mo ago
  The memory is in-package, not on-die - on-die would mean that the DRAM is being manufactured on the same 1-2-3-4-whatever nanometer process - DDR is much larger.

> On most x86 cores the limit is around 6 GB/s and about 20 GB/s for Apple M chips. What makes M-series have 3x the bandwidth (per core), over x86?

MindSpunk 10mo ago

M-series have a substantially wider memory bus allowing much higher throughput. It's not really an x86/M-series thing, rather it's a packaging limitation. Apple integrates the memory into the same package as the CPU, the vast majority of x86 CPUs are socketed with socketed memory. Apple are able to push a wider bus at higher frequencies because they aren't limited by signal integrity problems you encounter trying to do the same over sockets and motherboard traces. x86 CPUs like the Ryzen AI Max 395+, when packaged without socketed memory, are able to push equally wide busses at high frequencies.

Analemma_ 10mo ago

The sibling comment has the correct, more detailed answer, but the high-level answer is that the M-series chips are SoCs with all the RAM on-die. That lets you push way more data than you can over a bus out to socketed memory. The tradeoff is that it's non-upgradeable, but (contra some people who claim this is only a cash-grab by Apple to prevent RAM upgrades) it's worth it for the bandwidth.

Scaevolus 10mo ago
Apple had soldered DDR ram for a long time that was no faster than any other laptop. It's only with the Apple Silicon M1 that it started being notably higher bandwidth.
- vlovich123 10mo ago
  There were always technical benefits like lower power consumption iirc
eru 10mo ago
> The tradeoff is that it's non-upgradeable, but (contra some people who claim this is only a cash-grab by Apple to prevent RAM upgrades) it's worth it for the bandwidth. That, and if you come at it from the phone / tablet or even laptop angle: most people are quite ok just buying their computing devices pre-assembled and not worrying about upgrading them. You just buy a new one when the old one fails or you want an upgrade. Similar to how cars these days are harder to repair for the layman, but they also need much less maintenance. The guy who was always tinkering away with his car in old American sitcoms wasn't just a trope, he was truth-in-television. Approximately no one has to do that anymore with modern cars.
fanf2 10mo ago
It isn’t on-die, the ram is separate chips in the same package. See the pics about halfway down https://www.apple.com/de/newsroom/2023/10/apple-unveils-m3-m3-pro-and-m3-max-the-most-advanced-chips-for-a-personal-computer/ https://www.apple.com/de/newsroom/2023/10/apple-unveils-m3-m...
15155 10mo ago
The memory is in-package, not on-die - on-die would mean that the DRAM is being manufactured on the same 1-2-3-4-whatever nanometer process - DDR is much larger.