CS01-09 Computer Science Coming soon
Negative numbers and two's complement
CS01-09
This lesson is coming soon.
In this lesson
Explain how a computer represents unsigned and two's complement signed integers, and convert between denary and 8-bit two's complement across the range -128 to +127.
What it covers
- Unsigned 8-bit holds 0 to 255; signed 8-bit holds -128 to +127
- The most significant bit as the sign bit: 0 positive, 1 negative
- Converting a positive denary value to 8-bit two's complement
- Converting a negative denary value: write the positive, flip every bit, add 1
- Reading a two's complement pattern back to denary
- Why the range is asymmetric - there is one more negative than positive
Key words
For: Edexcel GCSE 1CP2
On the specification
| Board | Spec | Statement |
|---|---|---|
| Edexcel GCSE 1CP2 | 2.1.2 | Explain how computers represent and manipulate unsigned integers and two's complement signed integers. |
For teachers
This GCSE Computer Science lesson teaches negative numbers and two's complement. By the end, students should be able to explain how a computer represents unsigned and two's complement signed integers, and convert between denary and 8-bit two's complement across the range -128 to +127. It works through three worked examples and the mistakes examiners report.