Segmentation in Operating System 

 Segmentation kya hota hai?

Segmentation ek memory management technique hai jisme Operating System process ko logical parts (segments) me divide karta hai — jaise:

• Code Segment – program ke instructions

• Data Segment – variables aur constants

• Stack Segment – function calls, return addresses, etc.

Har segment alag-alag size ka hota hai, kyunki unka kaam aur data alag hota hai.

Segmentation me memory ko logically divide kiya jata hai, fixed size me nahi — yeh Paging se alag hai.

 Segmentation ki zarurat kyu padti hai?

Real programs ka structure logical hota hai — unme different parts hote hain:

Agar sabko same size ke fixed blocks me rakhoge (jaise Paging me), to kuch memory waste ho sakti hai.

 Segmentation se:

• Logical grouping possible hai

• Memory ko efficiently use kiya ja sakta hai

• Har segment alag manage aur protect kiya ja sakta hai

 Paging vs Segmentation

 Segmentation kaise kaam karta hai?

 Step 1: Process ko segments me baanto

Example:

• Segment 0: Code – 1000 bytes

• Segment 1: Data – 500 bytes

• Segment 2: Stack – 300 bytes

 Step 2: Segment Table banao

Operating System ek Segment Table banata hai har process ke liye, jisme likha hota hai:

• Base = Segment RAM me kaha se start ho raha hai

• Limit = Segment ka size kitna hai

 Step 3: Address Translation (Logical to Physical)

CPU logical address bhejta hai in 2 parts:

Operating System karta hai:

1. Segment Number se Segment Table me Base aur Limit nikaalta hai

2. Check karta hai ki Offset < Limit hai ya nahi

3. Agar valid hai → Physical Address = Base + Offset

4. Agar Offset zyada ho gaya →  Segmentation Fault

 Example:

• Logical Address = Segment 1, Offset = 100

• Segment 1 ka Base = 4000

• Offset = 100
   100 < 500 (Limit)

 Physical Address = 4000 + 100 = 4100

Agar Offset = 600 hota:
  600 > 500 → Segmentation Fault (invalid memory access)

 Segmentation Flow Diagram:

 Real-Life Example 

Socho tumhara school bag (memory) hai.
Usme alag-alag compartments (segments) hain:

• Books → Code

• Stationery → Data

• Lunchbox → Stack

Har cheez ka alag segment hota hai. Tumhe pata hai kis item ko kis compartment me rakhna hai — yehi segmentation ka concept hai.

 Advantages

-> Logical program structure maintain hota hai
-> Har segment alag protect aur access control ke saath manage hota hai
-> Programmer ko memory structure clearly samajh aata hai
-> Internal fragmentation nahi hota (kyunki sizes exact hote hain)

 Disadvantages

-> External Fragmentation – Memory ke beech khaali space chhut sakti hai
-> Segment Table banana aur maintain karna complex ho sakta hai
-> Memory allocation variable hone ki wajah se OS ka kaam thoda mushkil hota hai

 Summary Table