A software product license grants you the legal right to run or access a software program. A license agreement governs the use of licensed software.

Microsoft licenses software in three primary ways:

• Full Packaged Product - Retail
  Full Packaged Product (FPP) is boxed, shrink-wrapped software. Licenses for this type of software are acquired through retail outlets or through an online vendor.
  
  This type of software is best suited to personal or low-volume needs. For users running software on five or more machines, a volume licensing solution can save you both time and money.
• Original Equipment Manufacturer (OEM)
  OEM software, such as any Windows operating system, comes pre-installed on your new computer. Operating systems and other software applications are available through the OEM channel.
• Volume Licensing
  Microsoft Volume Licensing programs offer companies of all sizes a great way to buy and manage multiple software licenses - from five to thousands of licenses for software.
  
  Microsoft Volume Licensing programs provide potentially substantial savings, ease of deployment, flexible acquisition, numerous payment options, and other benefits such as Software Assurance.

CAL Guide

If your company’s workstations are networked, you will utilize a network server and the workstations on the network will access that server(s) software to perform certain functions such as file and print sharing.

In order to legally access this server software, a client access license or CAL may be required. A CAL is not a software product; rather it is a license that gives a user the right to access the services of the server.

Due to the technical nature of server products, CAL licensing can be a complicated area. Also, different types of CAL licenses are offered with different Microsoft Server products.

• Per seat
• Per server
• Per processor licensing
• Per mailbox licensing (education customers only)

Read more about how CALs apply to Microsoft Server products.