Cloud computing allows users to access computer resources like storage and processing power over the internet rather than locally. Major cloud companies include Google, Dropbox, Apple, and others. While public clouds offer resources over the internet, private clouds operate within a company's internal network and offer more security. The cloud reduces IT costs and improves mobile access and collaboration but also raises security and compatibility concerns as information is stored externally. Virtualization is a related concept that allows multiple operating systems to run on a single machine.