Rails Server needs restart every time i make changes ? why ?

Rails Server needs restart every time i make changes ? why ?

Every time I change anything in controller's or in models, I have to
restart the server for it to take effect.But that wasn't always the case,
it used to work normally before, when I changed anything, but i don't know
what happened now ?
In my development environment file i have set config.cache_classes = false.
Please help..