BARI — Assistant Maintenance Engineer — Exam: 10.05.2024প্রশ্ন ও সমাধান

A multithreading system allows a single process to run multiple threads concurrently, sharing the same memory space (code, data, and open files) while each thread keeps its own program counter, register set, and stack.

graph TD
    P[Process] --> T1[Thread 1]
    P --> T2[Thread 2]
    P --> T3[Thread 3]
    T1 -.shares.- M[(Shared Memory - Code, Data, Files)]
    T2 -.shares.- M
    T3 -.shares.- M

• Why it matters: threads are much cheaper to create and switch between than whole processes (no separate address space to set up), so multithreading gives concurrency with lower overhead.
• Types: User-level threads (managed by a library, unaware to the kernel) vs Kernel-level threads (managed and scheduled directly by the OS, can truly run in parallel on multiple cores).
• Example: a web browser uses separate threads for rendering the page, handling user input, and downloading resources — all simultaneously, within one process.
• Challenges: shared memory means threads must coordinate access to shared data (via mutexes/semaphores) to avoid race conditions.

Exam takeaway: multithreading = multiple lightweight threads within one process sharing memory — enables concurrency at lower cost than multiprocessing, but requires synchronisation to avoid race conditions.

Answer: 12 collision domains — one per switch port.

A collision domain is a network segment where only one device can transmit at a time without its signal colliding with another's. Unlike a hub, which forwards every incoming signal to all ports (creating one single shared collision domain for the whole hub), a switch intelligently forwards frames only to the correct destination port and maintains a separate collision domain per port.

graph TD
    S[12-port Switch] --> P1[Port 1 - own collision domain]
    S --> P2[Port 2 - own collision domain]
    S --> P3[Port 3 - own collision domain]
    S --> Pdots[... continues to Port 12]

Number of collision domains = number of switch ports = 12

Device	Collision domains created
Hub (N ports)	1 (shared by all ports)
Switch (N ports)	N (one per port)
Router	1 per interface (also separates broadcast domains, unlike a switch)

• Note the important distinction: a switch multiplies collision domains (one per port) but does not separate broadcast domains — all switch ports remain in the same broadcast domain unless VLANs are configured.

Exam takeaway: every switch port = its own collision domain (a hub has just one for the whole device); a 12-port switch therefore creates 12 collision domains.