the concept of bandwidth

Thanks bishop and solo. But how about if I host my own site using a webserver in my room ? what happen to the issue of monthly download limit ?

No download limits in this case. But if you have a high number of visitors, and your hosting video, audio, large files then speed might suffer since it depends on your ISP's UPLOAD speed. Which is usually less than the download speed (remember, user download is upload from your side).

If this is just a personal website or a small business with low expected traffic, it should be OK running it from home.

Now I am beginning to fit the pieces,it is the hosting company that implements a kind of technology to set bandwidth limit for clients, so that a particular client doesn't get bandwidth greedy. Business wise I don't think they charge people for bandwidth, the money they charge for disk space will make up for it. It might also means that big Internet businesses will prefer to host themselves for economic reasons.