Client access licenses
A Client Access License (CAL) is a kind of software license that legally permits client computers to connect to Microsoft server software. They usually come in the form of a certificate of authenticity (CoA) and a license key, which is sometimes attached to the certificate itself. The various editions of most of Microsoft’s server software usually include a small number of CALs, and this allows the software to be used by either a few users or a few computers, depending on the CAL licensing mode. If more connections to the server are needed, then additional CALs must be purchased.
Some Microsoft Server products require one CAL per concurrent connection, whereby one CAL is required for each unique client connection at any point in time. For example, consider a small business network where the computers are used by ten people, but there are never more than five people on site using the computers at any one time. In this scenario, only five CALs are needed. However, some of Microsoft’s products and licensing modes require a CAL for each unique client regardless of how many will be connecting at any single point in time. Some of Microsoft’s server software programs do not require CALs at all, as is the case of Windows Server Web Edition.