Process Model Modes

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1

When you install ASP.NET on a server running Windows Server 2003, ASP.NET applications are executed by IIS 6.0. IIS 6.0 runs in one of two distinct modes of operation, called application isolation modes. These are worker process isolation mode, the default, and IIS 5.0 isolation mode. IIS functions differently in the two isolation modes.

When ASP.NET runs in the worker process isolation mode, it runs in the W3wp.exe worker process and picks up the IIS 6.0 application pool process properties for its operation.

When running on IIS 6.0 in worker process isolation mode, ASP.NET uses the IIS 6.0 process model settings. For information about how to migrate ASP.NET process model configuration settings to IIS 6.0 application pool settings, see "Configuring IIS 6.0 to Host ASP.NET Applications" in Migrating IIS Web Sites to IIS 6.0.

When you configure IIS 6.0 to run in IIS 5.0 isolation mode, ASP.NET runs in its own process model, Aspnet_wp.exe, and uses its own configuration settings. These settings are stored in the computer-wide Machine.config configuration file.

In almost all situations, ASP.NET applications running on Windows Server 2003 should be run in worker process isolation mode. If your application uses read raw data filters, you should use IIS 5.0 isolation mode instead.

When installed on servers running Windows XP or Windows 2000 Server, ASP.NET runs in IIS 5.1 or IIS 5.0, respectively, and runs in the Aspnet_wp.exe process by default. The ASP.NET process model provides process recycling, health detection, and support for affinities between worker processes and particular CPUs on a server with multiple CPUs. For more information, see Using the ASP.NET Process Model.


You must be a member of the Administrators group on the local computer to perform the following procedure or procedures. As a security best practice, log on to your computer by using an account that is not in the Administrators group, and then use the runas command to run IIS Manager as an administrator. At a command prompt, type runas /User:Administrative_AccountName "mmc %systemroot%\system32\inetsrv\iis.msc".


To configure IIS 6.0 for IIS 5.0 isolation mode

  1. In IIS Manager, double-click the local computer, right-click Web Sites, and then click Properties.

  2. On the Service tab, select the Run WWW service in IIS 5.0 isolation mode check box, and then click OK. The Internet Services Manager dialog box appears.

  3. To start the Web service, click Yes.


When you have completed this procedure, you must restart the Web service, which will temporarily interrupt the service.