The correct answer is option 'C' - program status word.

Explanation:
- Program Status Word (PSW) is a register that contains the status information in a computer system.
- PSW is a special register that is used to store the current status of the processor and the operating system.
- It is also known by different names in different architectures, such as Processor Status Word (PSW), Condition Code Register (CCR), or Flag Register.
- PSW is typically a 16-bit or 32-bit register and is divided into several fields or flags that represent different aspects of the system's status.
- These flags indicate various conditions or modes of operation, such as whether the processor is in supervisor mode or user mode, whether an interrupt is pending, whether an arithmetic operation resulted in an overflow or carry, and so on.
- The PSW is updated by the processor based on the outcome of various instructions or events that occur during program execution.
- It is used by the processor to make decisions, control the execution flow, and handle exceptions or interrupts.
- The PSW can be read by the operating system or user programs to determine the current state of the system and take appropriate actions.
- For example, if a program wants to check if an arithmetic operation has resulted in an overflow, it can read the overflow flag in the PSW to determine this.
- Similarly, the operating system can use the PSW to determine the current mode of the processor and enforce access control or privilege levels.
- In summary, the PSW is a register that contains the status information in a computer system and is used by the processor and operating system to control and manage the system's execution.