this post was submitted on 08 Nov 2023
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I'm really interested in this kinda thing, do you have sources I can read?
What I found was DDR5 runs at a max of 64 GB/s, and the M2 Pro runs at 400 GB/s. ~~I can't find anything about it being faster due to running in parallel.~~ Edit:I found it, looks like the M2 Ultra runs at 800 GB/s, cool. If I'm reading correctly, this was done by connecting two M2 Pros
Also, the PS5 allegedly has over 400GB/s bandwidth just for perspective
Note those are comparing different numbers.
The number you quoted was for a single memory channel.
A processor has as many memory channels as it feels like. So that 800 number basically means about 16 channels. The M2 plain seems to be about two channels.
For comparison, x86 desktop CPUs have long been 2 channel designs. You go up the stack and you have things like EPYC having 12 channels.
So for single socket design, apple likely has a higher max memory performance than you can do single socket in x86 (but would likely turn in lower numbers than a dual socket x86 box).
So to clarify, the M2 Ultra runs at 800 GB/s because it's utilizing multiple memory channels, which is like running dual/quad/etc. channel RAM in an x86 PC. So at the max 64 GB/s bandwidth of DDR5 ram, you could run quad channel and get 256 GB/s right? And getting up to 12 channels of DDR5 could mean a bandwidth of 768 GB/sec?
Yeah, in that case Apple is definitely over charging. To be fair, my mb can't run 12 channels of RAM but it also won't cost me an arm and a leg and a kidney to have similar performance per GB
Note that I can't think of modem four channel x86. Either they are the usual two channel (two dimms per channel is how four dimm slots are organized) or have way more (Sapphire Rapids, Bergamo)
To map the M2, the base is about the same as most x86 consumer grade, the Pro is about Threadripper, and the ultra is somewhere between single or dual socket Bergamo, at least in terms of memory bandwidth, which is a highly specific metric.
Oh gotcha, thanks for straightening me out on that. I'm still learning tech so the examples are really helpful
The PS5 uses a unified 16gb of GDDR6, which has really high bandwidth for graphics applications. Apple is full of shit about their LPDDR5.