Teach Computing

Revision notes, activities, lesson plans, teaching ideas, and other resources for GCSE, A-Level, and IB Computer Science teachers and students.

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CommandPoint CAD

CommandPoint by Northrop Grumman offers a range of CAD systems for various ...

CAD+911 System

TriTech Software Systems is a company that specialises in Computer Aided Di...

London Ambulance CAD failure

The 1992 London Ambulance Service CAD failure is probably the most notoriou...

Washington State 911 Failure

A 911 emergency telephone system in Washington State and Oregon shut down f...

London ambulance failure (2017)

A 2017 failure of a London ambulance dispatch system is believed to have le...

Computer Aided Dispatch outage

A 911 system failure left emergency calls unanswered and is said to have co...

Load balancing videos

This short article and the associated video explain 5 load balancing algori...

Intergraph Computer-Aided Dispatch (I/CAD

Intergraph Computer-Aided Dispatch (I/CAD) is a system offering many of the...

Boolean logic worksheet pack

These three Boolean logic worksheets have exam style questions on logic sta...

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Binary Number System

Click here for recommended AQA A-Level Computer Science textbooks.

Unsigned binary

Binary to decimal

Binary-Decimal Conversions

This video contains lots of examples of converting binary numbers to decimal numbers, and vice versa. A good revision guide.


Updated: 2018-02-17

Unsigned binary arithmetic

Binary addition

Binary Addition & Overflow

Another excellent video from ComputerPhile with their usual clear explanations and worked examples. This video recaps binary numbers and then explains how to perform binary addition. It also deals with the potential problem of overflow and how it can be handled.


Updated: 2015-04-29

Signed binary using two’s complement

Two's Complement

Why we use Two's Complement

This video explains how to represent negative numbers in binary. It explains why we can't use a simple sign bit to represent positive or negative numbers, and then looks at how one's complement solves this problem. Finally it explained how two's complement works and why it is used. Although the beginning of the video goes into a lot of detail, it is useful to understand exactly why two's complement is needed and used.


Updated: 2015-04-29

Numbers with a fractional part

AQA A Level computer science

A-Level appendix unit - PG Online

Floating point numbers, adders, D-type flip flops are covered in this free lesson resource unit from PG Online. The presentations and activities are designed for the AQA AS and A-Level courses, but the content is relevant to other A-Level courses too.


Updated: 2017-10-17

A-Level only content

Rounding errors

Absolute and relative errors

Range and precision

Normalisation of floating point form

Underflow and overflow