guys I wanna make a pseudo-OS in the browser

why? Imagine you had "try Debian" or "try Ubuntu" sites like you have for tryerlang and other programming languages
so my question is, can javascript write and read files from the user? even if only limited to a folder like %appdata%
or will I have to use something like Flash?

I'm tired of the browser. I have an operating system for a reason. Sooner or later, some blowhard will replace the operating system with the browser, and we will have to start from scratch.

It's already happened, its called MOZILLA FIREFOX OS