MGMCL (Maddhapara Granite Mining Company Limited) Assistant Manager (ICT) Exam: 20.05.2022 (BUET)প্রশ্ন ও সমাধান

HTTP (HyperText Transfer Protocol) transmits data between browser and server in plain text, so anyone intercepting the traffic can read it. HTTPS (HTTP Secure) is HTTP layered over TLS/SSL encryption, so data is encrypted in transit and the server's identity is verified via a digital certificate.

Aspect	HTTP	HTTPS
Security	No encryption, plain text	Encrypted (TLS/SSL)
Default port	80	443
Data integrity	Vulnerable to tampering (man-in-the-middle)	Protected — tampering is detectable
Server identity	Not verified	Verified via an SSL certificate
Browser trust/SEO	Marked "Not Secure" by browsers	Shows a padlock icon, preferred by search engines
Performance	Slightly faster (no encryption overhead)	Minor overhead, negligible on modern hardware

Exam takeaway: HTTPS equals HTTP plus TLS/SSL — it adds encryption, data integrity, and server authentication, which is why it is mandatory for any site handling passwords, payments, or personal data.

Context switching is the mechanism by which the CPU switches from executing one process (or thread) to another, saving the state of the current process so it can be resumed exactly where it left off later.

Steps:

1. An interrupt, system call, or scheduler decision occurs while process P1 is running.
2. The OS saves P1's current context (program counter, registers, stack pointer) into P1's PCB (Process Control Block).
3. P1's PCB is moved to the appropriate queue (ready or waiting).
4. The scheduler selects the next process, P2, from the ready queue.
5. The OS loads P2's saved context from P2's PCB into the CPU registers.
6. The CPU resumes executing P2 from exactly where it had previously stopped.

sequenceDiagram
  participant CPU
  participant PCB1 as PCB (P1)
  participant PCB2 as PCB (P2)
  Note over CPU: P1 Running
  CPU->>PCB1: Save P1's context (interrupt occurs)
  CPU->>PCB2: Load P2's context
  Note over CPU: P2 Running
  CPU->>PCB2: Save P2's context (interrupt occurs)
  CPU->>PCB1: Reload P1's context
  Note over CPU: P1 resumes running

Context switching enables multitasking, but it is pure overhead — no useful computation happens during the switch itself, so an OS aims to minimize both the frequency and the cost of context switches.

Exam takeaway: a context switch saves the current process's state to its PCB and loads the next process's state from its PCB — essential for multiprogramming, but a performance cost, since the CPU does no useful work during the switch itself.