Why does a 32-bit OS support 4 GB of RAM?

Question

Just reading some notes in a purdue lecture about OSs, and it says:

A program sees memory as an array of bytes that goes from address 0 to 2^32-1 (0

Answer 1

1. 32bits can represent numbers 0..2^32 = 0..4,294,967,296
2. 32bits can address up to 2^32Bytes (assuming Byte-size blocks)
3. 2^32Bytes is the max size

2^32B = 4,194,304KiB = 4,194MiB = 4GiB