Keyboard

• Settings -> Keyboard -> Key repeat rate controls at what speed when pressing a key the input is sent, if you make it high, cursor will move faster when you press let's say down key etc.

Safe mode boot

• To boot in safe mode, shutdown the mac
• Keep pressing the power button till, it loads startup option
• Select the drive and continue

Directories

• ~/Library/Caches all system wide caches for applications
• ~/Library/Preferences plist files