Operating Systems flashcards, generated for you.

Software that manages hardware resources and provides services to applications. Acts as intermediary between users/programs and physical hardware (CPU, memory, disk, I/O).

Preemptive: OS can forcibly remove a running process to give CPU to another (context switching). Non-preemptive: process runs until it voluntarily yields control. Preemptive is fairer but has higher overhead.

Switching CPU execution from one process to another by saving/restoring registers and memory state. Costs: CPU cache invalidation, TLB flushes, memory overhead—all waste CPU cycles doing no useful work.

Excessive page faults where OS spends most time swapping pages to/from disk instead of executing processes. Occurs when working set exceeds physical memory—system becomes CPU-starved.

Isolation (separate address spaces) prevents one process crashing others but requires expensive IPC (pipes, sockets, shared memory). Tight coupling (shared memory) is fast but one fault can cascade. Most OS choose isolation for stability.

Process: independent execution unit with own memory space, file descriptors, heap, stack. Thread: lightweight execution unit within a process sharing memory/resources. Threads are faster to create/switch but share memory (race condition risk).

Ensuring only one process/thread accesses a critical section at a time, preventing data corruption. Primitives: mutex (mutual exclusion lock), semaphore, monitor, atomic operations—all prevent concurrent access.

Circular wait where processes hold resources and block waiting for resources held by others—system halts. Four conditions: mutual exclusion, hold-and-wait, no preemption, circular wait. All must be true; break one to prevent deadlock.

Small pages: fine granularity, less internal fragmentation, more page table entries (memory overhead). Large pages: coarser granularity, more internal fragmentation, smaller page tables. Interviewers want: larger pages reduce overhead but waste memory.

User mode: restricted CPU state, processes cannot execute privileged instructions or access hardware directly. Kernel mode: full CPU access, OS code runs here. Transition via system calls—expensive due to context switch and security checks.