Operating Systems

Step 1: Understanding system calls.
System calls provide an interface between user programs and the operating system kernel, allowing controlled access to system resources.
Step 2: How system calls are triggered.
User programs cannot directly execute kernel-level instructions. Instead, they trigger a controlled transfer of control to the kernel.
Step 3: Role of software interrupts.
This transfer is typically achieved using a software interrupt or trap instruction, which switches the CPU from user mode to kernel mode.
Step 4: Final conclusion.
Hence, system calls are usually invoked using software interrupts.

Step 1: Understanding context switching.
A context switch occurs when the CPU switches from executing one process to another. To resume execution later, the state of the current process must be saved.
Step 2: Identifying what must be saved.
The CPU state includes the program counter, stack pointer, and general-purpose registers, as these are essential to resume the process correctly.
Step 3: Role of the Translation Look-aside Buffer (TLB).
The TLB is a hardware cache used to speed up virtual-to-physical address translation. Its contents are not part of the process state and are often flushed or overwritten during a context switch.
Step 4: Final conclusion.
Therefore, the Translation Look-aside Buffer is not necessarily saved during a context switch.

Step 1: Understanding process states.
In an operating system, a process can be in states such as Ready, Running, Blocked (Waiting), or Terminated. Each state represents the current activity or condition of the process.
Step 2: Analyzing the I/O operation.
When a process performs an I/O operation, it cannot continue execution until the I/O operation is completed. Therefore, it must wait for the I/O device to finish its task.
Step 3: Identifying the correct state.
A process that is waiting for an I/O operation to complete is placed in the Blocked (or Waiting) state. It is neither Ready nor Running during this time.
Step 4: Final conclusion.
Hence, a process performing I/O must be in the Blocked state.