Basic Electronics

Say you're working on a hobby project but you're unsure how to power it. This little article from the Ethiopian Review runs down your various options. Here's an except, about linear regulation,

Wall-wart and battery voltages vary with time and load. Yet, electronic circuits generally demand tightly regulated voltage rails, often with tolerances of±5%. A voltage regulator converts a varying input voltage into a relatively static output. There are numerous regulator circuits and components. The easiest and, arguably, the most reliable solution is to use an off-the-shelf integrated linear regulator. Linear regulators convert a higher voltage to a lower voltage by dissipating the difference as heat. This is not the most efficient method, but it works well for situations of low to moderate power consumption. Linear regulators work without hassle because they do not require many external components or careful tweaking and they do not produce noise as do switching regulators.

The whole article is worth checking out!