Simply put, the labels 16-bit, 32-bit, or 64-bit, when applied to a microprocessor, characterize the processor’s data stream. You may have heard the term 64-bit code; this designates code that operates on 64-bit data.
In more specific terms, the labels 64-bit, 32-bit, and so on designate the number of bits that each of the processor’s general-purpose registers (GPRs) can hold. So when someone uses the term 64-bit processor, what they mean is a processor with GPRs that store 64-bit numbers. And in the same vein, a 64-bit instruction is an instruction that operates on 64-bit numbers that are stored in 64-bit GPRs.
Figure 9-1 shows two computers, one a 32-bit computer and the other a 64-bit computer.
In Figure 9-1, I’ve tried ...