Web Design in a Nutshell, 3rd Edition

HTTP response header

Once the server locates the file, it sends the contents of that file back to the browser, preceded by some HTTP response headers. The headers provide the browser with information about the arriving file, including its media type (also known as its content type or MIME type). Usually, the server determines the format from the file’s suffix; for example, a file with the suffix .gif is taken to be an image file.

The browser reads the header information and determines how to handle the file, either displaying it in the window or launching the appropriate helper application or plug-in. MIME types are discussed further at the end of this chapter.