asp tutorials, tutorials, sample code, and Microsoft news from 15Seconds
Data Access  |   Troubleshooting  |   Security  |   Performance  |   ADSI  |   Upload  |   Email  |   Control Building  |   Component Building  |   Forms  |   XML  |   Web Services  |   ASP.NET  |   .NET Features  |   .NET 2.0  |   App Development  |   App Architecture  |   IIS  |   Wireless
Pioneering Active Server
 Power Search

Subscribe Now!
Free Newsletter
Code Samples
DL Archives
List Servers
Mailing List
Tech Jobs
15 Seconds
Site Map
Privacy Policy
Internet News
Small Business
Personal Technology

Corporate Info
Tech Jobs
E-mail Offers

Compare products, prices, and stores at Hardware Central!

Web Site Compression
By Wayne Berry
Rating: 4.1 out of 5
Rate this article

  • email this article to a colleague
  • suggest an article


    As IT professionals try to reduce the cost of operating their Web sites, they should consider reducing the amount of bandwidth usage. Current compression technologies can do this; however, their implementation is limited by current bugs in both the browser and the server. Learn how to successfully compress your HTML output and save money on your monthly bandwidth.


    Depending on the file type, you can get up to a 90% compression ratio, and the overall average bandwidth saving is two to three times. This means if you are paying $300 per mega byte per second for your bandwidth with a monthly bill of $1200, you can reduce your bill to $400 per month. Interestingly enough Internet Service Providers can provide the same service while reducing their overhead using HTTP compression.

    How It Works

    Internet Explorer 4.0 and above and Netscape 3.0 and above have the ability to decompress responses from Web servers that send a compressed response. This decompression feature is built directly into the browser, doesn't require a plug-in, and is enabled by default. Browsers with this feature signal the Web server by sending a request header called "Accept-Encoding:". Internet Explorer sends the header as "Accept-Encoding: gzip, deflate" and Netscape sends the header as "Accept-Encoding: deflate". Each indicates the type of compression that they can decompress.

    Deflate is a format of data that represents the compressed page. It is not a compression technique. Different compression techniques can create different outputs; however, they usually produce the outputs in the deflate format. GZip is a format of wrapping the compressed page for transmission which include a ten byte header, followed by the compressed bytes, in a deflate format, usually followed by a checksum and original files size. Interestingly enough the first two bytes of any gzip file are the same, 0x1f followed by 0x8b. The third byte is the compression format (0x08 is deflate).

    Figure 1 : GZip Format

    When the Web server handles a request with a request header of "Accept-Encoding:" it has a choice, either to send a compressed page or a standard non-compressed page. If the Web server decides to send a compressed page, it responds with a response header called "Content-Encoded:" and the type of encoding as the value. For example, "Content-Encoded: gzip". The browser uses this header to determine if the content is encoded and decompresses it before rendering it to the user.

    Figure 2 : Compressed HTTP Request/Response

    Web Server Load

    In order for the server to respond with a compressed page, the page needs to be compressed. Compression happens in two distinct ways: for static requests, the page can be compressed ahead of time and served to multiple requests. For dynamic pages, like Active Server pages or Cold Fusion pages, the response has to be compressed on every request, since the output is different for every request.

    Since compression takes time, roughly 100 - 1000 milliseconds for every page depending on size and compression quality, compressing static pages ahead of time and severing them to multiple requests saves CPU cycles and makes for faster responses. Compressing dynamic pages is harder on the server, since all requests need compression and none can be done ahead of time.

    File Types

    Different types of file compress differently. Files that are already compressed or that have a random set of bits do not compress well, while files that have a lot of white space or text compress very well.

    For example, jpgs and gifs are already compressed, so compressing those files do not save any space. However, HTML can be compressed up to 90%. You can't compress PDF, because the Adobe Acrobat reader can not handled compressed file, see "The Bad News" below.

    IIS 5.0

    IIS 5.0 allows you to compress static pages, dynamic pages, or both. The compression option is turned off by default. To turn it on follow these instructions:

    1. Open The IIS Manager
    2. Navigate To the Computer Node
    3. Right Click and Choose Properties
    4. Click On the Edit for Master Properties
    5. Choose the Server Tab.
    6. At the bottom there is a HTTP Compression Group
    7. Check the "Compress Application Files" to get the Active Server Pages or Cold Fusion Pages Compressed
    8. Check the "Compress Static Files" to get your HTML files compressed.

    Figure 3 : Setting Up IIS Compression

    IIS 5.0 implements its compression via an ISAPI Filter called C:\WINNT\System32\inetsrv\compfilt.dll that is installed at the computer level. This means compression is activated for all of the web sites that this machine is hosting. If the HTTP Compression group in this tab is grayed out you might be missing the compression filter. To reinstall it see: Manual Installation of Compression Filter Fails (Q223176).

    By default, IIS 5.0 Compression will only compress files with an extension of "htm," "html," and "txt," since these files have the most potential for compression. However, you can tell IIS to compress requests with other extensions.

    Here is how:

    1. Open a Command Prompt session.
    2. Change the directory to your \InetPub\AdminScripts folder.
    3. Enter the following commands:

      CSCRIPT.EXE ADSUTIL.VBS SET W3Svc/Filters/Compression/GZIP/HcFileExtensions "htm" "html" "txt" "doc" "ppt" "xls"

      CSCRIPT.EXE ADSUTIL.VBS SET W3Svc/Filters/Compression/DEFLATE/HcFileExtensions "htm" "html" "txt" "doc" "ppt" "xls"

    5. Close the Command Prompt session.

    For more information read: How to Specify Additional Document Types for HTTP Compression (Q234497).

    When you turn on static compression, the IIS filter writes all the compressed files to a temporary location, by default it is: C:\WINNT\IIS Temporary Compressed Files, these files are reused until the origin file changes. This prevents static files from having to be recompressed for every request and save CPU cycles. However the default option is to use unlimited space on your C: drive. This is not recommended since it will run your drive out of space. Make sure to change this setting to something reasonable for your system.

    The Bad News

    Both Internet Explorer 5.5 and Internet Explorer 6.0 have a bug with decompression that affects some users. This bug is documented in: the Microsoft knowledge Base articles, Q312496 is for IE 6.0 (Not Yet Published), the Q313712 is for IE 5.5. Basically Internet Explorer doesn't decompress the response before it sends it to plug-ins like Adobe Photoshop. This means that Adobe Photoshop sometime crashes Internet Explorer if it gets a compressed page. Microsoft is offering a fix for this problem, to get it you need to call Microsoft product support and reference Q313712.

    Even though Microsoft has documented the problem and issued a fix this is very little help, since millions of people are running these browsers with this problem and are unwilling to install this fix. It would really be nice if Microsoft issued a fix for the server side.

    The Good News

    Though this is a bug with the browser, there is a server side solution that will work around the browser problem. If the server passes the HTTP response headers in a different way, the browser plug-ins will not get the compressed data, and the browser will decompress and render the pages successfully. However, currently there is no fix for IIS 5.0 compression filter.

    There are other compression filters that are made by 3rd parties that will do HTTP compression. These filters have more features and workaround the IE browser problem. XCache is one of these. XCache can be applied to single or multiple web sites and it will cache the static files in RAM as well as on disk without the worry of running out of disk space. With XCache you can choose which files you want to compress and what file types.


    Deflate Compression Format:
    GZip File Format:
    Using HTTP Compression On Your IIS 5.0 Web Site:
    HTTP Compression Speeds up the Web:

    About the Author

    Wayne Berry is the architect of XCache Technologies' XCache and XTune. He is a former Microsoft design engineer, founder of 15 Seconds, and one of the top Active Server Page developers in the country. Berry's expertise includes software design, performance consulting, development, marketing, and online business. Berry served as a software development engineer at Microsoft and as editor of 15 Seconds prior to founding XCache Technologies. A popular speaker, Berry has been invited to speak to international ASP developers' conferences, BackOffice Conference, and Internet World. He has authored several technical books, including ActiveX Programming Unleashed, Windows NT Registry Guide, and Special Edition Using Microsoft Internet Information Server 4.0, as well as many articles in print and online trade publications. Berry holds a B.S. in computer science from Western Washington University. Email him at

  • Rate This Article
    Not HelpfulMost Helpful
    1 2 3 4 5
    Supporting Products/Tools
    XCache combines dynamic content caching technology with content delivery network (CDN) support options, file compression and a whole lot of manageability features to help e-businesses deliver superior web site performance and reliability. You'll appreciate the administrative ease, your visitors will appreciate increased page delivery speed.
    XCompress works by compressing outgoing text between the Web server and the client. Page response times may improve by a factor of three or more while overall bandwidth use can drop by two thirds or more.

    XCompress runs on Windows 2000 and Windows NT 4.0 and is tightly integrated with Microsoft Internet Information Server (IIS) with MMC and COM interfaces.

    XTune 2.0 is the most powerful tuning application for IIS 4 or IIS 5 ever conceived. Indispensable to the enterprise and straightforward, this web tuning tool allows you to configure hidden operating system, network, Active Server Pages and Internet Information Server settings for better performance, without any additional hardware or software.

    This version scans your system more deeply, offering more performance-enhancing recommendations and greater insight into your web architecture. The Performance Wizard guides and teaches you throughout the complete tuning process, so you can learn while making your box run better than ever.

    Purchase here.

    Other Articles
    Aug 25, 2005 - Performance Monitoring in SharePoint Portal Server 2003
    Performance monitoring helps organizations identify performance bottlenecks. The problem is that with so many performance numbers available, how do you know which ones to watch? This article helps you identify which are the critical performance counters in a SharePoint Portal Server environment and explains how to monitor them. By monitoring performance regularly, organizations can recognize performance trends as they develop and prevent problems before they get out of hand.
    [Read This Article]  [Top]
    Aug 12, 2004 - Middle-Tier Hosting: Enterprise Services, IIS, DCOM, Web Services, and Remoting
    There is broad-reaching debate about remoting, Web services, Enterprise Services, and DCOM. In short, it is a debate about the best technology to use when implementing client/server communication in .NET. Rocky Lhotka shares his thoughts on the issue while offering clear explanations of basic application architecture terminology.
    [Read This Article]  [Top]
    May 18, 2004 - ASP.NET 2.0 Caching Features
    This article examines some of the new and exciting caching features in ASP.NET 2.0 and shows how to implement them in Web applications.
    [Read This Article]  [Top]
    Feb 12, 2004 - Case Study:
    When it came time to find a technology for its massive upgrade, chose .NET. Has the online dating service's partnership with Microsoft been as successful as the relationships it has established for many of its millions of members? Read on ...
    [Read This Article]  [Top]
    Jan 15, 2004 - Database Performance Philosophy
    Longtime 15Seconds discussion list member Tore Bostrup offers valuable advice on designing databases and applications for efficient querying.
    [Read This Article]  [Top]
    Dec 29, 2003 - Caching Oracle Data for ASP.NET Applications
    Narayan Veeramani shows how ASP.NET developers can improve application performance by caching data stored in an Oracle database and keeping the cached data in sync with the data in the Oracle database.
    [Read This Article]  [Top]
    Dec 2, 2003 - Leveraging MSMQ in ASP.NET Applications
    Ever developed a Web application that requires extensive processing? Ever had long running Web pages that often time out in the browser? Greg Huber reveals a simple technique that uses Microsoft Message Queuing (MSMQ) and the System.Messaging framework to handle long running Web processes.
    [Read This Article]  [Top]
    Feb 6, 2002 - The Just Two Theory on Web Servers
    Maintaining a large Web farm is both costly and unnecessary. Learn how to reduce your Web farm to just two servers in this controversial article by Wayne Berry.
    [Read This Article]  [Top]
    Aug 14, 2001 - NT Authentication's Impact on Connection Pooling
    Steve Witkop examines OLE DB and ODBC connection pooling when used with Microsoft NT LAN Manager Web server authentication.
    [Read This Article]  [Top]
    Jul 16, 2001 - Removing Duplicates in a String List
    Members of the 15 Seconds discussion list put together a couple of scripts to benchmark methods for removing duplicate items in a string list.
    [Read This Article]  [Top]
    Mailing List
    Want to receive email when the next article is published? Just Click Here to sign up.

    Support the Active Server Industry