Let's say a person has an 8 bit adder; They enter 255 (11111111), and save it to ram somehow. Next, a person subtracts 0 - 1, and gets 11111111 (Assuming overflow is ignored, like in many conventional subtractors), and they save it to ram. If the computer is read back moments later, the two numbers will be indiscernible. So, how would a person store (Or, even differentiate) negative and positive numbers?