“When it comes to monitoring your Mac’s status,such as the CPU or RAM usage, you have a couple different options. You can use menu bar applications which are often costly, or Dashboard widgets that are inconvenient to access. If neither of these sound like good options to you, monitoring your system with Activity Monitor might be a good option. It’s free, (after all, it’s built into Mac OS X), and it lets you display handy information right from the dock icon. In this video, I’ll show you how to set it up.”
via Cult of Mac:
Monitor Your Mac’s Status From The Dock [Video How-To] | Cult of Mac.