Following are the functions of operating system:

1. Program Execution:

Operating systems handle many kinds of activities from user programs to system programs like printer spooler, name servers, file server, etc. Each of these activities is encapsulated as a process.

2. I/O Operation:

An I/O subsystem comprises of I/O devices and their corresponding driver software. Drivers hide the peculiarities of specific hardware devices from the users. An Operating System manages the communication between user and device drivers.

3. File System Manipulation:

A file system is normally organized into directories for easy navigation and usage. These directories may contain files and other directions. 

Following are the major activities of an operating system with respect to file management:

• Program needs to read a file or write a file.
• The operating system gives the permission to the program for operation on file.
• Permission varies from read-only, read-write, denied and so on.
• Operating system provides an interface to the user to create/delete files.
• Operating system provides an interface to the user to create/delete directories.
• Operating system provides an interface to create the backup of file system,

4. Communication:

In case of distributed systems which are a collection of processors that do not share memory, peripheral devices, or a clock, the operating system manages communications between all the processes. Multiple processes communicate with one another through communication lines in the network. 

Following are the major activities of an operating system with respect to communication:

• Two processes often require data to be transferred between them.
• Both the processes can be on one computer or on different computers, but are connected through a computer network.
• Communication may be implemented by two methods, either by Shared Memory or by Message Passing.

5. Error Detection:

An error may occur in CPU, in I/O devices or in the memory hardware.

Following are the major activities of an operating system with respect to error detection:

1. The OS constantly checks for possible errors.
2. The OS takes an appropriate action to ensure correct and consistent computing.

6. Resource Management.

In case of multi-user or multi-tasking environment, resources such as main memory, CPU cycles and files storage are to be allocated to each user or job.

Following are the major activities of an operating system with respect to resource management:

• It acts like a resource manager. The OS manages all kinds of resources using schedulers.
• CPU scheduling algorithms are used for better utilization of CPU.

7. Protection:

Protection refers to a mechanism or a way to control the access of programs, processes, or users to the resources defined by a computer system. 

Following are the major activities of an operating system with respect to protection:

• The OS ensures that all access to system resources is controlled.
• The OS ensures that external I/O devices are protected from invalid access attempts.
• The OS provides authentication features for each user by means of passwords.