"MUS" is not a recognized operating system abbreviation in common use. Operating systems are software programs that manage computer hardware and provide services for computer programs. Examples of well-known operating systems include Windows, macOS, Linux, and Unix. "MUS" does not correspond to any widely used operating system.

Integrated circuits (ICs) were first introduced during the third generation of computers. The third generation of computers, which emerged in the 1960s, saw the development and widespread use of integrated circuits. These tiny electronic circuits contained multiple transistors, resistors, and capacitors on a single semiconductor chip. The use of integrated circuits significantly reduced the size of computers, increased their processing speed, and improved their reliability, marking a significant advancement in computer technology.

1. DOS is not an example of a mobile operating system.

2. Android Android (Android Droid) and Apple iOS (Apple iOS) is a mobile operating system.

3. Mobile operating systems are operating systems that run on mobile devices such as smartphones, tablets, and smartwatches.