I think it's mostly the memory bandwidth though that makes the GPUs so fast with LLMs. My card does about 1TB/s. CPU RAM won't come near that. I'm sure a lot of optimisations can be had but I think GPUs will still be significantly ahead.
Macs are so good at it because Apple solder the memory on top of the SoC for a really wide and low latency connection.
This is a good and valid comment. It is difficult to predict the future, but I would be curious what the best case theoretical performance of an LLM on a typical x86 or ARM system with DDR4 or DDR5 RAM. My uneducated guess is that it can be very good, perhaps 50% the speed of a specialized GPU/RAM device. In practical terms, the CPU approach is required for very large contexts, up to as large as the lifetime of all interactions you have with your LLM.
Macs are so good at it because Apple solder the memory on top of the SoC for a really wide and low latency connection.