OS X Mavericks

Choose About this Mac from the Apple menu, click on More Info, and check the model identifier against the following, which are the earliest Macs of each type that can run Mountain Lion and Mavericks:

iMac7,1

MacBook5,1

MacBookPro3,1

MacBookAir2,1

Macmini3,1

MacPro3,1

Xserve3,1

A computer incapable of running Mountain Lion which has a Core 2 Duo(not Core Duo) or better CPU and at least 2GB of RAM can run Lion 10.7, which is available by clicking here. Neither Mavericks nor Lion support PowerPC software such as Microsoft Office 2004.

Is your Mac Pro 2008 or later ? > OS X Mavericks: System Requirements

OS X Mavericks: System Requirements

Learn about the system requirements for OS X Mavericks.

To install Mavericks, you need one of these Macs:

• iMac (Mid-2007 or later)
• MacBook (13-inch Aluminum, Late 2008), (13-inch, Early 2009 or later)
• MacBook Pro (13-inch, Mid-2009 or later),
• MacBook Pro (15-inch or 17-inch, Mid/Late 2007 or later)
• MacBook Air (Late 2008 or later)
• Mac mini (Early 2009 or later)
• Mac Pro (Early 2008 or later)
• Xserve (Early 2009)

Your Mac also needs:

• OS X Mountain Lion, Lion, or Snow Leopard v10.6.8 already installed
• 2 GB or more of memory
• 8 GB or more of available space