Paul Stewart of PacketU comments:

We cover all sorts of different topics on this site. Today, we are starting a multipart series on subnetting. These concepts  are fundamental building blocks for network administrators, engineers and architects. The  subnetting topics outlined in this series  should be well understood prior to moving into advanced design or configuration topics. Moreover, the underlying technical concepts of this subject should be understood prior to utilizing  any  shortcuts to calculate subnet addresses and useable address space.

A great introduction to subnets for those that need to brush up on it before taking a networking exam.

Read more at: IP Subnetting Part 1: What is a Subnet?