4.3: Binary Addition

Exam Board:

Eduqas / WJEC


2016 + 

What is binary addition?

Binary addition is a method of adding binary values without having to convert them into denary.

How to add binary numbers:

Overflow Errors

What is an overflow error?

An overflow error occurs when a binary value is too large to be stored in the bits available.


In technical terms, an overflow error occurs if a carry (remainder) is present on the most significant bit (MSB). 

The CPU then sets the overflow flag to true.

The most significant bit (MSB) is the largest bit (always the one furthest to the left) of a binary value (e.g. 128 for an 8 bit value).

A flag is an alert signal. It is either on or off. The overflow flag is turned on by the CPU when an overflow occurs.

Questo's Questions

4.3 - Binary Addition:

1a. Describe the terms 'most significant bit' and 'flag'. [2]

1b. Using the terms from 1a, explain what an overflow error is. [2]

2. Add together the following binary values. If an overflow error occurs you must state one has occurred.

  • a. 010110012 and 010001012  [2]

  • b. 110110112 and 010111012  [2]

  • c. 001101102 and 011010112  [2]

  • d. 110110112 and 010101112  [2]

  • e. 011011012 and 110101102  [2]

© CSNewbs 2020