IIS Glossary

IIS 6.0

This topic describes the technological vocabulary used in the IIS SDK. Many of these terms are familiar to developers, but have new or altered definitions in the IIS environment. If you are looking for a term that is not defined here, please see the glossary in the IIS User Documentation that comes with IIS Manager, or see the glossary in the IIS Resource Kit.



abstract class

In Windows Management Instrumentation (WMI), a class from which you cannot create an instance because it does not have a full implementation. An abstract class serves as a base class from which other classes can inherit properties and methods. Also see concrete class.

Active Directory Service Interfaces (ADSI)

A directory service model and a set of Component Object Model (COM) interfaces. ADSI enables Windows applications and Active Directory clients to access several network directory services, including Active Directory. ADSI is supplied as a software development kit (SDK). Also see Windows Management Instrumentation (WMI).

Active Server Pages (ASP)

A Web-oriented technology developed by Microsoft that is designed to enable server-side (as opposed to client-side) scripting. Active Server Pages are text files that can contain not only text and HTML tags as in standard Web documents, but also commands written in a scripting language (such as VBScript or JavaScript), that can be carried out on the server.

Admin Base Objects (ABO)

A distributed COM (DCOM) object that implements the IMSAdminBase interface methods that enable an application to manipulate IIS metabase. ABO is often confused with admin objects.

admin objects

Used with ADSI and WMI. There exists an admin object for each type of configuration entity, for example, the IIsWebService admin object represents the Web service for the purposes of configuration, and the IIsWebVirtualDir admin object represents any virtual directory. Individual virtual directories are differentiated by their Location property, for example, /LM/WSVC/1/Root/vdir1 and /LM/WSVC/1/Root/vdir2 are both defined as IIsWebVirtualDir objects, but they are different virtual directories defined at different nodes in the metabase. Admin objects are often confused with Admin Base Objects (ABO).


application isolation

The separation of applications by process boundaries that prevent the applications from affecting one another. Application isolation is configured differently for each of the two Internet Information Services (IIS) isolation modes on IIS 6.0: IIS 5.0 isolation mode and worker process isolation mode. See also in-process, out-of-process, pooled-process.

application pool

A grouping of one or more URLs (or Web sites as they are represented in IIS) served by a worker process.

IIS 4.0, IIS 5.0, IIS 5.1: Application pools do not apply.

See also worker process isolation mode.




Common Gateway Interface (CGI)

An interface that is used by executable files that handle specific requests. An IIS server can execute a CGI, exchange data with the client via stdin and stdout, and get IIS server variables through environment variables.

Common Information Model (CIM)

An industry standard technique to represent systems, applications, networks, devices, and other managed components in an enterprise environment. Used by Windows Management Instrumentation (WMI) to access management information in an enterprise environment.

compatibility mode

Component Object Model (COM)

The object-oriented programming model that defines how objects interact within a single application or between applications. In COM, client software accesses an object through a pointer to an interface on the object.

concrete class

In Windows Management Instrumentation (WMI), a class from which you can create an instance because it has a full implementation. See also abstract class.

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Distributed COM (DCOM)

A wire protocol that enables software components to communicate directly over a network.

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high isolation

Also called out-of-process.See out-of-process.

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IIS 5.0 isolation mode

In IIS 6.0, an isolation mode that simulates the IIS 5.0 Web process model. Also called compatibility mode. See also application isolation, worker process isolation mode.


Internet Server API (ISAPI) extensions or ASP files that are hosted in the same process as IIS. Application modes can be set on the virtual directories that contain the ISAPI DLLs or ASP files. ISAPI filters always run in-process which means they run in the W3wp.exe process on IIS 6.0 in worker process isolation mode, and they run in the Inetinfo.exe process on IIS 4.0, IIS 5.0, IIS 5.1, and on IIS 6.0 in IIS 5.0 isolation mode. Also called low isolation. See also application isolation, out-of-process, pooled-process.

inheritable property

A metabase property in a parent node that trickles down to child nodes without having to be specifically set at the child nodes. Specifically setting the same property at a child node over-writes the inherited value. Also see inherited property.

inherited property

A metabase property in a child node that was inherited from its parent node. Inherited properties do not show up as being specifically set at the child node. Specifically setting the property at a child node over-writes the inherited value. Also see inheritable property.


See in-process.

Internet Server API (ISAPI)

An interface that resides on an IIS server for the purpose of initiating software services that are tuned for the Windows operating system. ISAPI is an API for developing extensions to Internet Information Services (IIS) and other Hypertext Transfer Protocol (HTTP) services that support the ISAPI interface. When an ISAPI DLL is used to generate content to display to a client, it executes faster than an ASP page (which is not compiled code) or a COM component. However, since ISAPI DLLs can only be written in C/C++, they are more difficult to develop.


ISAPI extension

An ISAPI DLL that handles a specific incoming request to the IIS server. ASP.dll and ASPNET_ISAPI.dll are examples of Microsoft?-provided ISAPI extensions. Extensions are loaded when first needed and kept in memory until the host process shuts down. Also known as ISAPIs.

ISAPI filter

An ISAPI DLL registered with Internet Information Services (IIS) that modifies the behaviour of the server. URLScan.dll is an example of a Microsoft?-provided ISAPI filter. Filters are loaded when the worker process starts and unloaded when the worker process shuts down. Also known as filters.

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In the IIS metabase: See node as defined for the IIS metabase.

In the Windows registry: A node in the registry. A key can contain subkeys and entries, for example, Environment is a key of HKEY_CURRENT_USER.

In IP security (IPSec): A value used in combination with an algorithm to encrypt or decrypt data. Key settings for IPSec are configurable to provide greater security.

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See node as defined for the IIS metabase.

low isolation

medium isolation


A hierarchical store of configuration information and schema that is used to configure IIS. The metabase performs some of the same functions as the system registry, but it uses less disk space.

IIS 6.0: In physical terms, the metabase is a combination of the MetaBase.xml and MBSchema.xml files. IIS works from an in-memory metabase that periodically generates the physical files.

IIS 5.1 and earlier: In physical terms, the metabase is a binary-formatted file.

Also see node.

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In the IIS metabase: A hierarchical container in the IIS metabase. Each node allows a specific set of properties to be configured at that location or path. For example, at the Web service node, identified by the IIsWebService admin object at the /LM/WSVC path in the metabase, certain properties like AppRoot can be set which affect the IIS Web service. A node is a child of another node if its path includes the path of the parent, for example, /LM/WSVC/1 is a child node of /LM/WSVC. A node in the metabase is also referred to as a key.

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Internet Server API (ISAPI) extensions or ASP files that are hosted in a separate process than IIS. On IIS 4.0, IIS 5.0, IIS 5.1, and on IIS 6.0 in IIS 5.0 isolation mode, ISAPI DLLs and ASP files run in a surrogate process called DLLHOST.exe, which is managed by COM+. Also called high isolation. See also application isolation, in-process, pooled-process.

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In the IIS metabase: See node.



On IIS 4.0, IIS 5.0, IIS 5.1, and on IIS 6.0 in IIS 5.0 isolation mode, a special Web Application Manager (WAM) package that hosts all out-of-process Internet Server API (ISAPI) extensions and ASP files that are set to medium isolation within the same DLLHOST.exe process, which is managed by COM+. Also called pooled out-of-process (POOL), or medium isolation. See also application isolation, in-process, out-of-process.

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A representation of the structure of something. Classes in Visual Basic and C++ can be said to be schemas of objects, and objects are instances of classes. In IIS, the metabase schema represents the structure of the metabase configuration file.

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Uniform Resource Locator (URL)

A naming convention that uniquely identifies the location of a computer, directory, or file on the Internet. A URL also specifies the appropriate Internet protocol, such as Hypertext Transfer Protocol (HTTP) or File Transfer Protocol (FTP). An example of a URL is http://www.microsoft.com.


URL mapping

The process of associating a Uniform Resource Locator (URL) with a physical directory. Also see virtual directory.

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virtual directory

A directory name, used in a URL (or Web) address, that corresponds to a physical directory on the server. In the URL http://www.microsoft.com/widgets, widgets is the virtual directory which is mapped to a physical directory on one of the http://www.microsoft.com servers. Sometimes called a URL mapping or a vdir.

virtual server

In Windows: In a server cluster, a collection of services that appear to clients as a physical Windows-based server but are not associated with a specific server. A virtual server is typically a resource group that contains all of the resources needed to run a particular application and that can be failed over like any other resource group. All virtual servers must include a Network Name resource and an IP Address resource.

In IIS: See Web site.

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Web Application Manager (WAM)

On IIS 4.0, IIS 5.0, IIS 5.1, and on IIS 6.0 in IIS 5.0 isolation mode, a COM+ application package that works with DLLHOST.exe to host out-of-process ISAPI extensions and ASP files. Provides communication between DLLHOST.exe and INETINFO.exe. See also application isolation, pooled-process, out-of-process.

Web site

A collection of content files or applications that can be viewed in an Internet browser (like Internet Explorer) when you type in a Uniform Resource Locator (URL) like http://www.microsoft.com. A Web site can contain many virtual directories. Also called a virtual server.

Web service extension restriction list

A list of ISAPIs and CGIs used by applications on the Web server, including their location, descriptive information, and a flag for determining whether the Web service extension is enabled or disabled.

IIS 5.0 and earlier: This feature is not available.

Windows Management Instrumentation (WMI)

The Microsoft implementation of Web-Based Enterprise Management (WBEM), which is an industry-wide standard technology for accessing management information about systems in an enterprise environment. WMI uses the Common Information Model (CIM) industry standard to represent managed components in a system. A system developer can develop a WMI interface that allows programmatic access to a system, so that users can write command-line administration scripts and tools. Also see Active Directory Service Interfaces (ADSI).


worker process

The implementation of the core Web server in IIS 6.0. Worker processes run in W3wp.exe. See also worker process isolation mode.

worker process isolation mode

The new Web process model for IIS 6.0 which allows for application pools. See also application isolation, IIS 5.0 isolation mode.