In a typical film/tv show (and many books), the local Lord/Sheriff/King etc, tends to have lots of men in chainmail/swords just hanging around, and often acting as a local police force, as well as protection of the lord/his assets.

In reality, how many people would be permanently retained as a guard in this manner? Would they also have other duties? What sort of equipment would they likely have?

Obviously this varies by region, era, and wealth of the individuals concerned. Answer by the time period/region that you are aware of answers for - knowledge of how it varies would be very interesting as well. This questions is in respect to medieval Europe, as that is the sort of fiction I am thinking of.