The computer's CPU can access each individual byte. It uses an address for each byte. Computer memory addresses start at zero and go up to the biggest number the computer can use. Older computers were limited in how much memory they could address. 32-bit computers can address up to 4GB of memory. Modern computers use 64 bits and could address up to 18,446,744,073,709,551,616 bytes = 16 exabytes of memory.