In SDD we need to know about three or four number systems:

Decimal number - our counting system, using numberal 0 - 9. This is our base 10 counting system that twe have used since before primary school.

Binary numbers - 0s and 1s. This is because of how computers process data, using transistors.

Hexadecimal number - base 16. We use Hex because it is a more convenient way of rendering binary. Every group of four binary digits can be rendered as a single hex digit. We see these in hex codes in Windows Error reports or memory dumps. They are also used extensively later in the topic when we discuss device drivers.

Hex number systems used integers 0-9, then A, B, C, D, E and F as the remaining single figit integers.

Octal numbers - base 8. Before CPUs could process four bits of data at a time, they processed three. This is why we still look at octal.

The presentation and video above show how to convert between these number systems.