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Apple's "unified memory" marketing is so strong that even tech literate people seem to have this misconception! They have managed to pull this sort of thing of
by fooker 14d ago
Apple's "unified memory" marketing is so strong that even tech literate people seem to have this misconception!
They have managed to pull this sort of thing off many many times. https://en.wikipedia.org/wiki/Reality_distortion_field https://en.wikipedia.org/wiki/Reality_distortion_field
- Rohansi 14d agoYup, the only reason Macs have higher memory bandwidth is because they use more memory channels, which gives them a wider bus. Both Intel and AMD only allow more than dual channel memory on server class processors these days.
- kstrauser 14d agoThe “Apple only does X better because they do Y” thing has been a meme for ages. I remember dismissals like “PowerPC is only faster at math because it has more integer units” or something along those lines, and thinking, uh, isn’t that a good thing?
- JohnBooty 14d ago"You're only better than me at sports because you practice more and try harder!"
- pixl97 14d agoDepends on the expense trade off. If I get 10% more performance for 50% more cost it really depends on one's needs, for example.
- Rohansi 14d agoI am just saying it's not magic and x86 is capable of doing the same. Quad channel memory used to be more common in consumer hardware but now it looks like you don't even have the option anymore for desktops. AMD's Strix Halo was the first sign to reversing that (it has quad channel memory!) and hopefully we see more of that in the future.
- colejohnson66 14d agoAMD does market segmentation and limits consumer chips to dual-channel. You need to cough up the dough and get Threadripper for quad-channel. Or even more for Threadripper Pro to get octa-channel.
- Rohansi 14d agoAs I mentioned above AMD's Strix Halo has quad channel memory and is consumer level. But yes, other than that everything is segmented away.
- torginus 14d agoAfaik steam deck is quad channel, despite it being a pretty low end chip (with a decent GPU though)
- Rohansi 14d agoKind of but not really. DDR5 splits your typical 64-bit channel into two 32-bit subchannels meaning the bus width is not increased. These subchannels are not always advertised because it's a just a feature of DDR5. Actually adding more channels increases bus width, which is what meaningfully improves memory bandwidth.
- pdpi 14d agoThere's a qualitative difference between "they're doing a different thing" and "they're doing the same thing, tuned differently". GP is saying that this is a case of "they just tuned it differently". This distinction doesn't change what the performance numbers look like today, but it does inform what changes would be necessary for those numbers to look different tomorrow. E.g. Apple Silicon isn't fundamentally orders of magnitude more efficient than x86, they just used smaller features. Newer Intel and AMD chips made on equivalent processes _also_ get similar efficiency gains.
- sroussey 14d agoThere are AMD and Intel devices on similar process (not talking about A20Pro or M6 which are set to ship later this week), and they do not get the same gains. And honestly, they have historically had different markets. When the design is for only one customer, you don't need to generalize things, and those things you generalize to give different customers different options has costs. AMD will soon be a larger customer for TSMC than Apple (NVIDIA is already there) so Apple's pre-booking new processes is likely to be gone in the near future.
- Dylan16807 13d agoThe point is that "unified architecture" is a buzzword unrelated to what actually makes things fast.
- Rohansi 13d agoIt does make some things faster because you can share memory between CPU, GPU, etc. without copying. But not everything.
- Kon5ole 14d agoThe memory bandwidth is a small thing compared to the massive win you get by not having to move data between two memory pools at all.
- Rohansi 14d agoDepends on your workload. And AMD has supported unified memory long before Apple Silicon existed anyway.
- fooker 14d agoOften you don't move memory around as a programmer, but that's exactly what happens in the background. It's the address space that's unified, not always the physical hardware. The data movement (when needed) is handled transparently in the background by page faults and other tricks.
- Rohansi 14d agoMoving memory around is a bottleneck. Non-unified memory usually means copying over the PCIe bus which is way slower than RAM (and way way slower than VRAM). Actually unified memory means you don't need to copy anything at all though which is the absolute best case for performance.
- deleted 13d ago[deleted]
- throwaway85825 14d agoExcept strix halo.
- PunchyHamster 14d agoThreadripper have that extra bandwidth and M5 still is faster
- Dylan16807 14d agoCan you link a specific benchmark? Keep in mind that non-Pro threadripper is still only 256 bits wide and Pro is 512. And the memory is 30% slower than with an M5. So an M5 Ultra has 3x the memory bandwidth of the best threadripper.
- Melatonic 14d agoDon't some AMD full server CPUs have 12 memory channels ?
- Dylan16807 13d agoYes, some do. So similar bandwidth to a Max but with lots of slower cores. Half as much as an Ultra.
- Kon5ole 14d agoHaving unified memory is a real advantage though, it's not a reality distortion.
- davrosthedalek 14d agoThe price is that you essentially glue CPU and GPU together, which limits total compute, from a size and thermal perspective. This is really not a limit because of unified memory -- in principle, PCIe GPUs could read/write main memory without the CPU. But it's a limit for /fast/ unified memory, because fast means close. So unified memory is great as long as the integrated GPU is strong enough. Then it has two advantages: a) probably faster transfer CPU<->GPU (but that's an implementation choice for the non-unified case b) If you either need a lot of memory for the CPU or the GPU, but not for both at the same time, you pay for memory only once.
- nvme0n1p1 14d agoAgreed. That's why it's a good thing all computers made in the past 15 years have unified memory, not just macs. https://x.com/Lina_Hoshino/status/1820947147312820497 https://x.com/Lina_Hoshino/status/1820947147312820497
- stymaar 14d agoIs that Marcan's vtuber persona (Asahi Lina) that changed name since Marcan doesn't work on Asahi Linux anymore?
- Kon5ole 14d agoIn theory perhaps but the benefit is not as relevant with a weak iGPU. In practice all PC's with performance ambitions had a dGPU until Strix Halo and Panther Lake.
- fooker 14d agoIt is a real advantage. The reality distortion is that people seem to believe it's HBM, or somehow it gives you extraordinary amounts of vram. Neither are really true.
- 14d ago
- nutjob2 13d agoNo I just failed to check before I posted, I thought it was HBM. I don't have any interest in Apple hardware so wasn't properly informed, and have been duly crucified.