Nothing except CPU manufacturer choices. Mac laptops use it and they're consumer products.
People will have to get used to buying a fixed amount of RAM with their CPU but thats unlikely to be a problem.
People will have to get used to buying a fixed amount of RAM with their CPU but thats unlikely to be a problem.
They have managed to pull this sort of thing off many many times. https://en.wikipedia.org/wiki/Reality_distortion_field
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.
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.
If I get 10% more performance for 50% more cost it really depends on one's needs, for example.
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.
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.
DDR is optimized for latency and stability at the cost of bandwidth whilst GDDR is optimized for bandwidth at the cost of latency and stability. GDDR is pushed so hard these days that a small percentage of errors is expected and corrected because this is still faster than running it slower but more accurate.
GDDR7 often has 10-20x the total bandwidth but 3x the latency of DDR5. Graphical workloads want as much bandwidth as possible but care relatively little for latency. Conversely, applications love low latency but don't really see any performance benefit from higher bandwidth.
So basicallyt you have workloads that are diametrically opposed and running unified memory forces you to compromise.
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.
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.
No, Mac laptops use LPDDR, currently LPDDR5X.