Chapter 3, is "architecture" referring to CPU or OS?

[StefanSalewski]

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When reading that section some weeks ago, I marked it as it was not quite clear:

Additionally, the isize and usize types depend on the architecture of the computer your program is running on, which is denoted in the table as “arch”: 64 bits if you’re on a 64-bit architecture and 32 bits if you’re on a 32-bit architecture.

As I am still unsure, I just asked GPT-4:

Is here, and generally, "architecture" referring to the hardware (CPU) or to the operating system? As we can run a 32-bit Windows on a 64-bit CPU.

See, and please clarify in the book:

https://chat.openai.com/share/3671d87f-458e-405b-a97f-87a91574cd95