> Really, 1TB/s of memory bandwidth to and from system memory?

5x is false, it's more like 4x. Apple doesn't use memory sticks, they use on-SoC dram ICs.

The M3 Ultra has 8 memory channels at 128-bit per channel for a total of 1024-bit memory bus. It uses LPDDR5-6400 so it has 1024-bit * 6400000000 bits = 819.2 gigabytes per second of memory bandwidth.

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menaerus 2 days ago | parent [-]

You're deceiving yourself and falling for Apple marketing. Regardless of a stick or SoC memory, which has been the case with pretty much SoC in 2010's (nowadays I have no idea), it is not possible to drive the memory with such high speeds.

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rowanG077 2 days ago | parent [-]

This is definitely citation needed. I very much expect a combined GPU/CPU/NPU load to saturate the memory channels if necessary. This is not some marketing fluff. The channels are real, the number of RAM ICs are physically there and connected.

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menaerus a day ago | parent | next [-]

We are talking about the memory bandwidth available to the CPU cores and not all the co-processors/accelerators present in the SoC so you're pulling in the argument that is not valid.

https://web.archive.org/web/20240902200818/https://www.anand...

> While 243GB/s is massive, and overshadows any other design in the industry, it’s still quite far from the 409GB/s the chip is capable of.

> That begs the question, why does the M1 Max have such massive bandwidth? The GPU naturally comes to mind, however in my testing, I’ve had extreme trouble to find workloads that would stress the GPU sufficiently to take advantage of the available bandwidth.

> Granted, this is also an issue of lacking workloads, but for actual 3D rendering and benchmarks, I haven’t seen the GPU use more than 90GB/s (measured via system performance counters)

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inkyoto a day ago | parent | next [-]

The cited article is pretty clear: the M1 Max maxes out at (approximately) 100 Gb/sec per a single CPU core, 243 Gb/sec per a CPU cluster, and 409 Gb/sec per the entire SOC.

They did not (or, rather, could not) measure the theoretical peak GPU core saturation for the M1 Max SOC because such benchmarks did not exist at the time due to the sheer novelty of such wide hardware.

	▲	menaerus a day ago \| parent [-]
		> The cited article is pretty clear: the M1 Max maxes out at (approximately) 100 Gb/sec per a single CPU core, 243 Gb/sec per a CPU cluster, and 409 Gb/sec per the entire SOC. So, which part of "We are talking about the memory bandwidth available to the CPU cores and not all the co-processors/accelerators present in the SoC" you didn't understand?

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rowanG077 a day ago | parent | prev [-]

Well I think we talked about memory channels and the maximum speed reachable. And you claimed it was marketing fluff. I don't think it's unreasonable to say that if that speed is reachable using some workload it's not marketing fluff. It was not clear at all to me you limited your claims to CPU speed only. Seems like a classic motte-and-bailey to me.

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Rohansi a day ago | parent | prev [-]

https://web.archive.org/web/20250125040351/anandtech.com/sho...

You're realistically going to reach power/thermal limits before you saturate the memory bandwidth. Otherwise I'd like to hear about a workload that'll make use of the CPU, GPU, NPU, etc. to make use of Apple's marketing point.