EGCB; Sub-Divisional Engineer (ICT) Exam: 28.01.2023 (BUET)প্রশ্ন ও সমাধান

A process moves through several states during its lifetime, managed by the OS scheduler.

stateDiagram-v2
[*] --> New
New --> Ready: admitted
Ready --> Running: dispatched by scheduler
Running --> Ready: interrupt / time-slice expired
Running --> Waiting: I/O or event wait
Waiting --> Ready: I/O or event completed
Running --> Terminated: process finishes
Terminated --> [*]

• New — the process is being created; its Process Control Block (PCB) is being set up.
• Ready — loaded in memory, waiting for CPU time in the ready queue.
• Running — instructions are actively executed by the CPU (only one process per core at a time).
• Waiting (Blocked) — cannot proceed until an event occurs (I/O completion, semaphore signal, etc.).
• Terminated (Exit) — execution has finished; the OS reclaims its resources.

Each process is tracked via its Process Control Block (PCB), holding its current state, program counter, CPU register values, memory limits, and scheduling information, updated at every state transition.

Exam takeaway: five canonical states — New → Ready → Running → (Waiting ↔ Ready) → Terminated; only the scheduler moves a process from Ready to Running, and only an I/O/event completion moves it from Waiting back to Ready.

The TCP/IP model (Internet Protocol Suite) is the practical 4-layer networking model underlying the modern Internet, describing how data is packaged, addressed, transmitted, routed, and received between devices.

graph TD
A[4. Application - HTTP, FTP, DNS, SMTP] --> B[3. Transport - TCP, UDP]
B --> C[2. Internet - IP, ICMP, ARP]
C --> D[1. Network Access / Link - Ethernet, Wi-Fi]

Layer (top to bottom)	Role	Example protocols
Application	User-facing services, data formatting, sessions	HTTP, FTP, DNS, SMTP, Telnet
Transport	End-to-end delivery, reliability, port numbers	TCP (reliable), UDP (fast, unreliable)
Internet	Logical addressing and routing between networks	IP, ICMP, ARP
Network Access (Link)	Physical transmission on the local network	Ethernet, Wi-Fi, PPP

• Maps roughly onto OSI's 7 layers — Application covers OSI's Application + Presentation + Session; Network Access covers OSI's Data Link + Physical.
• Each layer adds its own header as data moves down (encapsulation), and strips it as data moves up at the receiver (decapsulation).

Exam takeaway: TCP/IP = 4 layers (Application, Transport, Internet, Network Access) — the model that actually runs the Internet, versus OSI's 7-layer theoretical/teaching reference model.