(1) Any attribute, phenomenon or event that can have different qualitative or quantitative values. Typically, a form of metadata goes with the variable, there is a variable definition that describes what is varying and there is a value for the variable. Variables are typically assessed in a clinical trial.
When you click a link for an email address or website, your Mac opens the app you've set for that kind of link. Mail is the default email app and Safari is the default web browser on your Mac. If you install other email apps or web browsers, you might want to set them to open when you click an email link or web link. Open the Mail app.
MacBook Pro models running Mac OS X 10.5 Leopard or Mac OS X 10.6 Snow Leopard are capable of running essentially all Mac software written for Intel-based Macs and the vast majority of Mac OS X applications written for PowerPC-based systems using the Rosetta Universal Binary Translator.ll Unibody MacBook Pro models shipped with Mac OS X 10.5 Leopard or later which provides no support for Mac OS 9/Classic applications. If you have a mission critical application that only runs on Mac OS 9, you likely would be best served by maintaining a PowerPC-based Mac.