When an input file is opened, what are the possible errors that may occur?

- 1st condition may be that the file is protected against access, here it terminates abruptly.

- 2nd condition may be that file exists, then we need to create the output file.

- If file with the same name exists then it may be deleted or program may be aborted.

- In another case the system may ask the user to replace the existing file or abort the program.

Explain PCB.

- PCB, process control block, is also called as the task control block.

- It contains information about the process state like new, ready, running, waiting and halt.

- It also includes the information regarding the process priority and pointers to scheduling queues .

- Its counter indicates the address of the next instruction to be executed for the process.

- It basically serves as the storage for any information that may vary from process to process.