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Microsoft KB Archive/151307

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Knowledge Base

Client Access License (CAL)

Article ID: 151307

Article Last Modified on 2/21/2007


  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Server 3.5
  • Microsoft Windows NT Server 3.51
  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft File and Print Services for Netware 3.51

This article was previously published under Q151307


This article describes issues related to client access license.


There are two different licensing models that customers can choose, either a per server or per seat. The per server licensing (concurrent licensing) will cause Windows NT to implement a concurrency check to only allow the number of concurrent file/print users as configured in license manager. Per seat licensing does not implement the license manager check, though the customer must still purchase a client access license (CAL) for such clients.

The following uses require a CAL:

  • Server Message Block (SMB) file & print (Windows NT Server)
  • NCP file & print (FPNW)
  • Remote Access Service (RAS)
  • Services for Macintosh (SFM)

Examples of SMB connections are: connecting to a Windows NT server file share or printer share through Windows for Workgroups 3.11, a Microsoft Network client, a LAN manager client, or a Windows 95 client. A NetWare client access FPNW requires a separate CAL.

Note the following general exception to Windows CAL requirements. Windows CALs are not required when access to the server software is unauthenticated and conducted through the Internet. Authenticated access is defined as an exchange of user or application credentials between the server software and a user or device. An example of this exception is if unidentified users browse your public Web site. Windows CALs are not required for those users.

For information about Microsoft Windows Server 2003 client access licensing, visit the following Microsoft Web site:

Additional query words: CAL

Keywords: KB151307