What exactly does Attach() do in Entity Framework?

Possible Duplicate:
Entity Framework 4 - AddObject vs Attach

I've seen the use of attach a few times, especially when manipulating models.

using (var context = new MyEntities())
{
    context.Attach(client);
    context.SaveChanges();
}

From the context it looks like it just runs an UPDATE against a record in EntityFrameworks, but I also see it used in DELETE statements. So I can only assume it just gets a pointer to the database?

Could someone point me in the right direction, I've googled it for a while and whilst I don't come up empty, I can't find any good explinations of what it does (from an overview, and internally).