In Controlling : Difference Between Product Cost By Order and Product Cost by Period

Hi SAP Guru's,

I'm asking Common Question to all but Actually i want Exact Difference Between Product Cost by Order and Product Cost Period, Actually  i know Product cost By Order main Cost Object is manufacture Order, in Product cost by Period Product is Cost Object also we can use mulltifull  BOM here it's Right or Wrong Please Explain me?

Also Explain With Example Easily Understood My Self and some Freshers also Understand.

Thanks and Regards,

Sriaknth