A Level Computer Science OCR Practice Exam

What is the main purpose of Two's Complement?

1. To represent only positive numbers

2. To store negative numbers as binary digits

3. To calculate decimal numbers efficiently

4. To perform complex logic operations

The correct answer is: To store negative numbers as binary digits

The main purpose of Two's Complement is to store negative numbers as binary digits. In computing, binary representation is used for numbers, and Two's Complement provides a way to express both positive and negative integers. In the Two's Complement system, the most significant bit (MSB) acts as a sign bit, where 0 indicates a positive number and 1 indicates a negative number. This method allows for a seamless representation of negative numbers because when you take the Two's Complement of a binary number, you invert the bits and add one. This operation effectively shifts the negative value into a form that can be added with other binary numbers without special treatment or additional logic. This representation has advantages, such as allowing for straightforward arithmetic operations like addition and subtraction without needing separate circuits for handling positive and negative values. It simplifies the hardware design of arithmetic logic units (ALUs) in computers. The other choices, while relevant to binary systems, do not capture the primary function of Two's Complement. Representing only positive numbers pertains to unsigned binary formats, while calculating decimal numbers efficiently is more about how numbers are processed rather than how they are stored. Performing complex logic operations also suggests a broader scope of functionality beyond simply representing negative values.