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Is the full memory bandwidth actually available to the CPU on M-series CPUs? Because that would seem like a waste of silicon to me, to have 200+ GB/s of past-LL
by formerly_proven 2y ago
Is the full memory bandwidth actually available to the CPU on M-series CPUs? Because that would seem like a waste of silicon to me, to have 200+ GB/s of past-LLC bandwidth for eight cores or so.
- adrian_b 2y agoI do not know for the latest models, but at least in M1 the CPU was limited to a fraction of the total memory throughput, IIRC to about 100 GB/s.
- inkyoto 2y ago100 Gb/sec per a CPU core. 200+ Gb/sec (IIRC Anandtech measured 240 Gb/sec) per a cluster. Pro is one cluster, Max is two clusters and Ultra is four clusters, so the accumulative bandwidth is 200, 400 and 800 Gb/sec respectively[*]. The bandwidth is also shared with GPU and NPU cores within the same cluster, so on combined loads it is plausible that the memory bus may become fully saturated. [*] Starting with M3, Apple has pivoted Pro models into more Pro and less Pro versions that have differing memory bus widths.