Difference bitween Html and Html5

DOCTYPE is much longer as HTML4 is based on SGML-based.
DOCTYPE is required to enable standards mode for HTML documents.
<!DOCTYPE html>
Audio and Video are not part of HTML4 specification Audio and Videos are integral part of HTML5 specifications e.g. <audio> and <video> tags
Vector Graphics is possible with the help of technologies such as VML, Silverlight, Flash etc. Vector graphics is integral part of HTML5 e.g. SVG and canvas
It is almost impossible to get true GeoLocation of user browsing any website especially if it comes to mobile devices. JS GeoLocation API in HTML5 helps identify location of user browsing any website (provided user allows it)
Browser cache can be used as temporary storage. Application Cache, Web SQL database and Web storage is available as client side storage. Accessible using JavaScript interface in HTML5 compliant browsers.
Web Sockets are not available. Generally used mechanisms are long polling and streaming. Full duplex communication channels can be established with Server using Web Sockets. Accessible using JavaScript interface in HTML5 compliant browsers.
Works with all old browsers Most of modern browser have started supporting HTML5 specification e.g. Firefox, Mozilla, Opera, Chrome, Safari  etc.
Does not allow JavaScript to run in browser. JS runs in same thread as browser interface. Allows JavaScript to run in background. This is possible due to JS Web worker API in HTML5