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> Memory interface width of modern CPUs is 64-bit (DDR4) and 32+32 (DDR5). Sure, per channel. PCs have 2x64 bit or 4x32 bit memory channels. Not sure I get your point, yes PCs have 64 bit cache lines and apple uses 128. I wouldn't expect any noticeable difference because of this. Generally cache miss is sent to a single memory channel and result in a wait of 50-100ns, then you get 4 or 8 bytes per cycle at whatever memory clock speed you have. So apple gets twice the bytes per cache line miss, but the value of those extra bytes is low in most cases. Other bigger differences is that apple has a larger page size (16KB vs 4KB) and arm supports a looser memory model, which makes it easier to reach a large fraction of peak memory bandwidth. However, I don't see any relationship between Apple and PCs as far as DIMMS. Both Apple and PCs can (and do) solder dram chips directly to the motherboard, normally on thin/light laptops. The big difference between Apple and PC is that apple supports 128, 256, and 512 bit wide memory on laptops and 1024 bit on the studio (a bit bigger than most SFFs). To get more than 128 bits with a PC that means no laptops, no SFFs, generally large workstations with Xeon, Threadrippers, or Epyc with substantial airflow and power requirements |
Also important to consider that the RTX 4090 has a relatively tiny 384-bit memory bus. Smaller than the M1 Max's 512-bit bus. But the RTX 4090 has 1 TB/s bandwidth and significantly more compute power available to make use of that bandwidth.