[sparkie]

> By the time the 64-bit era rolled around, the "64-bits" definitely referred to address space.. The original Pentium had a 64-bit data path and had instructions (MMX, eg PADDQ) that could operate on 64-bit numbers - no one would call it 64-bit. By the early 2000s with the big push to mainstreaming 64-bit, it was all breaking out of the 4GB address space limitation - not the width of data.

We're ~20 years down the line and none of these "64-bit" processors support 64-bit addressing yet. Most support up to 48-bits of addressing, with some newer intel chips supporting 57-bit addresses with 5-level paging.

I always took the bit-ness of the processor to refer to the data bus size between the cpu and main memory, aka, the size of a machine word.