Explanation:

- Software routines:

- The correct answer is software routines. An operating system is primarily a collection of software routines that manage the hardware resources, provides an interface for user interaction, and serves as a platform for running applications.

- Input-output devices:

- These are hardware components that the operating system manages. The OS itself is not a collection of these devices.

- Hardware components:

- Hardware components are managed by the operating system but do not form the OS itself.

- All of these:

- This is incorrect, as an operating system specifically refers to software routines, not hardware or I/O devices.