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Based on my observations, google and probably many others are in love with websites that include the Etag and Last-modified headers along with the if-modified-since and if-none-match header checking because they contribute to higher speed browsing, however, back in the day, headers in use were namely Expires and Cache-control.

I read elsewhere that google chrome browser ignores cache-control sent by the server and uses a value of zero. Because of this, I'm going to stick with using Etag and Last-Modified headers.

My question is what are the first browsers and versions that support Etag, Last-modified, If-modified-since and If-none-match headers?

The reason why I ask is because my site for the most part is a site that displays photos but I don't want people with extremely old computers to throw them out and buy new ones just in order to view a set of pictures. I would rather build a very large set of happy guests instead.

  • Are you asking for which browsers first supported the headers individually, or together? Because if-modified-since has been around a long time. I remember back in the mid-1990s having all sorts of headaches the first time we had daylight saving in the Netscape 0.9x days, before there was 'force reload' (which told the client to not send an if-modified-since header). – Joe May 23 '15 at 0:57
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I read elsewhere that google chrome browser ignores cache-control sent by the server and uses a value of zero.

Citation please? The only reference I found of this is a SO question (June 2012) that states that Chrome will override Cache-Control if the user specifically refreshes the page - which is understandable.

This would also be strange since Google recommends Cache-Control headers in its developer guidelines. Cache-Control is the "newer standard" (although still quite old) and should take priority over other headers if present.

what are the first browsers and versions that support Etag, Last-modified, If-modified-since and If-none-match headers?

With regards to ETag / If-None_match, this question on SO (June 2011) states:

all browsers in popular use, IE5.5+, Safari, Chrome, Opera, and Firefox, all support the ETag/If-None-Match headers.

...but it will no doubt predate this list. (ETags were part of the original HTTP/1.1 spec formerly introduced in 1997.)

Last-modified / If-Modified-Since will certainly predate ETags. I would think the very early browsers would have supported these. This represents the basic fundamentals of any caching mechanism.

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