GNU GZip is a popular data compression program used to compress web pages before they are transmitted from the web server to the visitor’s browser.  The smaller, compressed data results in a much quicker delivery to the browser.  Compression is a simple and effective way to save bandwidth and speed up your Zen Cart store.

Once GZip compression is turned on, it all happens in the background.  The visitor’s browser sends a header telling the web server that it accepts compressed content.  The web server then sends a response if the content is actually compressed.  For example, that the data has been compressed by GZip.  Turning on GZip can make your store pages more than 70% smaller.

Before turning on the GZip Compression setting in Zen Cart though, we need to check if your store pages are already compressed via a setting on your web server.  The Zen Cart setting should be set to Off in this case as compressing already compressed data may cause additional errors.

Check your web server compression setting

There are a couple of ways of checking if your web host’s configuration includes compression. 

Zen Cart Admin

1. Log in to your Zen Cart store Admin
2. From the Tools menu, select Server/Version Info.
   
3. Check the setting for Output Buffering.
    

HTTP compression check

1. Visit http://www.whatsmyip.org/http_compression/.
2. Type in your store address and click the Test button.
   
3. The results will be displayed.
   

Setting GZip Compression in Zen Cart

If the above tests show that your web server is already configured for http compression, leave your Zen Cart settings as the default (Off).

If, however, you find that your store pages are not currently being compressed (as in the results above), then turning on GZip Compression will result in significantly smaller data sizes being delivered to your store visitor’s browser.

To turn on GZip Compression for your Zen Cart store:

1. Log in to your Zen Cart store Admin
2. From the Configuration menu, select GZip Compression.
   
3. Click on Edit to enable GZip Compression.  Select 1 to turn on GZip Compression and then click the Update button to save the setting.
   

Rerun the tests above to check that the GZip Compression has now been implemented for your store.

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