What does 80 and 51 indicate in 8051 microcontroller and upon which basis the AT89S51 has been designated?

Hello YAHOO,I need to prepare for my project viva and I wish to know the entire things of microcontrollers like types,manufactuing companies,how do they designate,hidden truths,special things and etc.Could you please help me in finding those answers?Also suggest related sites or books if any.