Why is logical space in a 32-bit system specified in bytes rather than bits?

Question

It is claimed in my textbook that in a 32-bit system, The instruction LDR r4,[r6] lets you address a logical space of 4GB.I know where the 4GB comes from, It is simply 2^32 / (1024 x 1024 x 1024). However, My question is why is it bytes and not bits? Why when we raise 2^32, we should talk about bits and not bytes.

Answer 1

Look at it like this :

1 bit can store 2^1 numbers (0 and 1)

2 bits can store 2^2 numbers (00, 01, 10, 11)

3 bits can store 2^3 numbers (000, 001, 010, 011, 100, 101, 110, 111)

and so on

so 32 bits can store 2^32 numbers (0 thru (2^32 - 1))

So if an address is 32 bits wide, you can potentially address 2^32 locations. An addressable location is a byte - its not a bit. We cannot have address of bit but the smallest addressable unit of memory is a single byte. Hence the 4GB.