A Level Computer Science OCR Practice Exam

How does 'Sign and Magnitude' represent negative numbers in binary?

1. By using a separate byte for the sign

2. By flipping the sign and adding 1

3. Using the first bit for sign, and the rest for magnitude

4. By using all bits for the magnitude

The correct answer is: Using the first bit for sign, and the rest for magnitude

In 'Sign and Magnitude' representation, negative numbers are expressed by designating the first bit (also known as the most significant bit) to indicate the sign of the number. If this first bit is set to 0, it signifies that the number is positive, while a 1 indicates that the number is negative. The remaining bits represent the magnitude of the number, which is the actual size of the value disregarding its sign. This method allows for a clear distinction between positive and negative values within a binary system, making it easier to interpret the data. The approach is straightforward because it essentially separates the sign from the actual value, maintaining a clear representation of both components. The other options do not accurately describe the 'Sign and Magnitude' method. For instance, using a separate byte for the sign or flipping the sign and adding 1 refers more closely to different methods of negative representation in binary, such as 'One's Complement' or 'Two's Complement', respectively. Lastly, using all bits for the magnitude would not allow for any representation of sign, which is a fundamental aspect of 'Sign and Magnitude'.