What is differences b/w Catalyst switches and IOS switch?

Catalyst Switches : Catalyst is a brand which intially sell it's swtiches to  users and use it's own operating system known as CAT OS instead of Cisco IOS.

IOS : CISCO has named it's operating system as Internetworking Operating System ( IOS ) .

In Past Decade Cisco has purchased many companies and one of them is Catalyst Brand . Then Cisco had just renamed their switches and sell it with their own name like cisco catalyst 1900,2800,2900,3550,3750 etc. and cisco had just installed their own operating system that is Cisco IOS ( Internetworking Operating System ) in them and they are also called as IOS Switch.