.NET Platform Interview Questions

🎯 Focus Areas

CLR internals, GC, JIT, assemblies, .NET versions. These appear in every senior .NET interview.

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Q1: What is CLR?

Common Language Runtime — the engine that runs .NET code.
Responsibilities:
  - JIT compilation (IL → native code)
  - Memory management and Garbage Collection
  - Exception handling
  - Thread management
  - Type safety verification
  - Security

Q2: What is IL / MSIL / CIL?

Intermediate Language — CPU-independent bytecode produced by the C# compiler.
Same IL runs on Windows, Linux, Mac → CLR converts to native code at runtime via JIT.

Q3: What is JIT compilation?

Just-In-Time — CLR compiles IL to native machine code on first method call.
Result cached — second call uses native code directly (fast).
Alternative: AOT (Ahead-of-Time) — compile at publish time, faster startup.

Q4: What is the difference between .NET Framework and .NET Core/.NET 5+?

.NET Framework → Windows only, closed source, v4.8 is final version
.NET Core       → Cross-platform, open source, high performance
.NET 5+         → Unified platform (Core + Framework merged), current standard

Rule: All new projects use .NET 8 (LTS). Framework only for legacy maintenance.

Q5: What is Garbage Collection and its generations?

GC automatically frees heap memory when objects have no references.
Gen 0 → short-lived (collected most often, ~every few seconds)
Gen 1 → survived Gen 0 (buffer between 0 and 2)
Gen 2 → long-lived static/cached objects (collected rarely)
LOH   → Large Object Heap — objects > 85KB

GC does NOT handle: file handles, DB connections, unmanaged resources
→ Use IDisposable + using for those.

Q6: What is the difference between managed and unmanaged code?

Managed   → runs under CLR, GC handles memory, type-safe (C#, VB.NET, F#)
Unmanaged → runs directly on OS, manual memory, no GC (C, C++, COM)
P/Invoke  → call unmanaged code from C# managed code

Q7: What is an Assembly?

.dll or .exe file containing:
  - IL code (compiled C#)
  - Metadata (type info, method signatures)
  - Manifest (name, version, dependencies)
  - Resources

.exe → has entry point, can run directly (console apps)
.dll → no entry point, referenced by other assemblies

Q8: What is a Namespace?

Organizes types to avoid naming conflicts.
SchoolManagement.Models.Student
SchoolManagement.Services.StudentService

using SchoolManagement.Models;  // import namespace
var s = new Student();          // no full path needed

Q9: What is LTS vs STS in .NET?

LTS (Long Term Support) → 3 years support (even versions: 6, 8, 10)
STS (Standard Term)     → 18 months support (odd versions: 7, 9, 11)

Use LTS for production. .NET 8 LTS (Nov 2023 – Nov 2026).

Q10: What is NuGet?

Package manager for .NET (like npm for Node.js, pip for Python).
Hosts 300,000+ packages at nuget.org.
dotnet add package Microsoft.EntityFrameworkCore.SqlServer

💡 Most Asked .NET Platform Questions

1. CLR responsibilities — memorize all 6
2. .NET Framework vs .NET Core — always asked
3. GC generations — Gen 0/1/2 and LOH
4. Managed vs Unmanaged code
5. What is an Assembly and what does it contain

🤖Use AI to Learn Faster

Use ChatGPT, Claude, or Copilot to go deeper on .NET platform interview questions. Try these prompts:

• "Ask me 10 .NET platform interview questions and evaluate my answers"
• "Explain CLR and JIT compilation like I am explaining it in an interview"
• "What .NET internals questions do companies ask for senior .NET roles?"
• "Quiz me on .NET versions — ask which version introduced which feature"

💡 Tip: After reading this article, paste your own code into AI and ask "What could go wrong here and why?" — fastest way to find edge cases and deepen understanding.