1. GCSE Computing#BristolMet Session Objectives#8 MUST add two 8-bit binary integers SHOULD explain overflow errors COULD provide solutions to limit overflow errors

2. GCSE Computing#BristolMet Adding binary numbers Adding binary numbers uses the same method as addition in Base10 where you carry 1 across e.g 3 6 7 + 2 8 4 6 5 1 Carry 1 1 However, in binary remember: Base 10 Binary 1 0 1 2 1 0 3 1 1 Therefore in 4 bit binary: 1 0 1 1 + 1 1 0 1 1 1 0 0 0 Carry 1 1 1 1 Requires another bit

3. GCSE Computing#BristolMet Overflow Overflow – when a number becomes too large to fit into the number of bits allocated it is said to ‘overflow’ and some bits are ‘lost’ leaving an incorrect value. For example: 1 1 0 0 0 0 1 0 + 1 0 1 1 1 0 1 0 0 1 1 1 1 1 0 0 Carry 1 1 In this case we need a 9 th column and if the computer only stored 8 bits to store numbers this would the carry from the 8 th column would be lost. This is called overflow – the calculation has overflowed the available space. REVISION: What is the largest number we can store in 8 bit binary?

4. GCSE Computing#BristolMet Adding binary examples TASK: Complete addition questions worksheet and test your answers using decimals ANSWERS Q1 Q2