application/x-www-form-urlencoded, the body of the http message sent to the server is essentially one giant query string -- name/value pairs are separated by the ampersand (
&), and names are separated from values by the equal symbal (
multipart/form-datadata is send in pairs too, but each pair is represented as a "part" in a mime message. Parts are separated by a particular string boundary (chosen specifically so that this boundary string does not occur in any of the "value" payloads). The value piece of each name/value pair is now the payload of each part of the mime message.
MIME message saves space, when dealing with large amounts with data, and first one - for short data.