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Configure Compression

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

To more efficiently use available bandwidth, it is advisable to enable IIS's HTTP compression feature. HTTP compression provides faster transmission time between compression-enabled browsers and IIS regardless of whether your content is served from local storage or a UNC resource. You can compress static files only, application response files only, or both static files and application response files. Compressing application response files is usually called dynamic compression.

By default, enabling static file compression compresses .htm, .html, and .txt files. Enabling dynamic compression compresses .asp, .dll, and .exe files. You can customize the file types that are compressed. See Customizing the File Types IIS Compresses for more information.

Enabling compression of static files in IIS always results in more efficient utilization of bandwidth and faster Web site performance. Enabling dynamic compression always results in more efficient utilization of bandwidth, but if your server's processor utilization is already extremely high, the CPU load imposed by dynamic compression might make your site perform more slowly.

If you already have a network-based compression solution installed, enabling compression in IIS might not result in bandwidth utilization or performance improvements, depending on whether the network-based compression and IIS-based compression are redundant. See Optimizing IIS 6.0 Performance for detailed information about the many compression configuration options available.

Requirements

  • Mode: This feature of IIS 6.0 is available whether IIS is running in worker process isolation mode or IIS 5 compatibility mode.

  • Credentials: Membership in the Administrators group on the local computer.

  • Tools: Iis.msc.

Procedures

To enable server-wide HTTP compression

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

  2. Click the Service tab, and in the HTTP compression section, select the Compress application files check box to enable dynamic compression.

  3. Select the Compress static files check box to compress static files.

  4. In the Temporary directory box, type the path to a local directory or click Browse to locate a directory. Once a static file is compressed, it is cached in this temporary directory until it expires, or the content changes. The temporary directory must be on a local drive on an NTFS-formatted partition. The directory cannot be compressed, and should not be shared.

  5. Under Maximum temporary directory size, click a folder size option. If you click the Limited to (in megabytes) option and enter a number in the text box next to it, IIS automatically cleans up the temporary directory according to a least recently used rule when the set limit is reached.

  6. Click Apply, and then click OK.

Note

If you notice a performance loss specific to serving dynamic content, disable compression of dynamic content.