(a) Process Control Block (PCB)

PCB is data structure per process maintained by kernel. Contents: Process ID, State (new/ready/running/waiting/terminated), Program Counter, CPU registers, Scheduling info (priority, queue pointers), Memory info (page tables, limits), I/O status (open files, devices), Accounting (CPU time, limits). Kernel uses PCB for context switch.

(b) Schedulers

• Long-term (Job scheduler): selects processes from job pool on disk to ready queue in memory. Controls degree of multiprogramming. Infrequent, slow. Absent in time-sharing.
• Medium-term: swapping — suspends/resumes processes to balance load, moves between memory/disk.
• Short-term (CPU scheduler): selects from ready queue to CPU frequently (ms). Must be fast; dispatcher then context-switches.
  Tradeoff: LT controls admission, MT handles memory pressure, ST ensures responsiveness.