What is Overflow?
When the result of a calculation is too large to fit in the available number of bits, an overflow error occurs. The extra bits are lost!
Example: 8-bit Overflow
8-bit can store: 0 to 255 (00000000 to 11111111)
What happens if we add 200 + 100?
11001000 (200)
+ 01100100 (100)
----------
¹¹¹¹¹¹¹ ← carries
1 00101100 (This would be 300, but...)
↑
This 9th bit doesn't fit in 8 bits!
Computer sees: 00101100 = 44 (WRONG!)
Overflow error! The carry out of the MSB is lost.
Detecting Overflow:
- Unsigned binary: Overflow if carry out of the MSB
- Real-world: Games showing "99999" max score, counters wrapping around
- Example: Pac-Man kill screen at level 256 (8-bit overflow: 255+1 = 0)
This key facts covers Overflow Errors - When Numbers Get Too Big within Binary Arithmetic for GCSE Computer Science. Revise Binary Arithmetic in 3.3 Data Representation for GCSE Computer Science with 15 exam-style questions and 18 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 4 of 11 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Binary Arithmetic
In binary addition, what is the result of 1 + 1?
Explain the effect of a logical left shift and a logical right shift on the value of a binary number.