Does READ UNCOMMITTED have the same effect as AUTOCOMMIT=1?

AFAIK running transactions as READ UNCOMMITTED means that there is no lock, so every change caused by a transaction is immediately visible to other transactions. Is it correct to assume that this is the same behaviour we get with any transaction if we enable AUTOCOMMIT? AFAIK in this case, as well, the effects of any query are immediately visible to others. Of course, the two concepts are somewhat different, semantically, but is there any difference in what's actually happening? I'm interested in a general answer, though I do tend to care more about MySQL and Microsoft SQL Server.