Client access license

A client access license (CAL) is a commercial software license that allow clients to use server software services. Most commercial client apps are licensed so that payment is required for each installation. However, some server products, which are accessed by multiple devices or users concurrently, are licensed so that payment is required for each concurrent use. Thus, each concurrent use is authorized with a client access license. For example, an instance of Windows Server 2003 for which ten CALs are purchased allows 10 concurrent connections.


Commercial apps are licensed to end users or businesses: in a legally binding agreement between the proprietor of the software (the "licensor") and the end user or business (the "licensee"), the licensor gives permission to the licensee to use the app under certain limitations, which are set forth in the license agreement. In case of Microsoft, the consumer retail or "off-the-shelf" products generally use very similar licence agreements, allowing the licensee to use the software on one computer, subject to the usual terms and conditions. For businesses however, Microsoft offers several types of licensing schemes for a range of their products, which are designed to be cost effective, flexible, or both. [1]

Commercial server software, such as Windows Server 2003 and SQL Server 2005 require licenses that are more expensive than those which are purchased for desktop software like Windows Vista. All clients that connect to these server products must have a license to connect in order to use their services. These special purpose licenses come in the form of a CAL.