**Segmentation in OS-**

Before you go through this article, make sure that you have gone through the previous article on **Segmentation in OS**.

We have discussed-

- Like
**Paging**, Segmentation is another non-contiguous memory allocation technique. - Segmentation divides the process into meaningful segments.
- Segment table stores the information about each segment of the process.

In this article, we will discuss a practice problem based on segmentation.

**PRACTICE PROBLEM BASED ON SEGMENTATION-**

**Problem-**

Consider the following segment table-

Segment No. | Base | Length |

0 | 1219 | 700 |

1 | 2300 | 14 |

2 | 90 | 100 |

3 | 1327 | 580 |

4 | 1952 | 96 |

Which of the following logical address will produce trap addressing error?

- 0, 430
- 1, 11
- 2, 100
- 3, 425
- 4, 95

Calculate the physical address if no trap is produced.

**Solution-**

In a segmentation scheme, the generated logical address consists of two parts-

- Segment Number
- Segment Offset

We know-

- Segment Offset must always lie in the range [0, limit-1].
- If segment offset becomes greater than or equal to the limit of segment, then trap addressing error is produced.

**Option-A: 0, 430-**

Here,

- Segment Number = 0
- Segment Offset = 430

We have,

- In the segment table, limit of segment-0 is 700.
- Thus, segment offset must always lie in the range = [0, 700-1] = [0, 699]

Now,

- Since generated segment offset lies in the above range, so request generated is valid.
- Therefore, no trap will be produced.
- Physical Address = 1219 + 430 = 1649

**Option-B: 1, 11-**

Here,

- Segment Number = 1
- Segment Offset = 11

We have,

- In the segment table, limit of segment-1 is 14.
- Thus, segment offset must always lie in the range = [0, 14-1] = [0, 13]

Now,

- Since generated segment offset lies in the above range, so request generated is valid.
- Therefore, no trap will be produced.
- Physical Address = 2300 + 11 = 2311

**Option-C: 2, 100-**

Here,

- Segment Number = 2
- Segment Offset = 100

We have,

- In the segment table, limit of segment-2 is 100.
- Thus, segment offset must always lie in the range = [0, 100-1] = [0, 99]

Now,

- Since generated segment offset does not lie in the above range, so request generated is invalid.
- Therefore, trap will be produced.

**Option-D: 3, 425-**

Here,

- Segment Number = 3
- Segment Offset = 425

We have,

- In the segment table, limit of segment-3 is 580.
- Thus, segment offset must always lie in the range = [0, 580-1] = [0, 579]

Now,

- Since generated segment offset lies in the above range, so request generated is valid.
- Therefore, no trap will be produced.
- Physical Address = 1327 + 425 = 1752

**Option-E: 4, 95-**

Here,

- Segment Number = 4
- Segment Offset = 95

We have,

- In the segment table, limit of segment-4 is 96.
- Thus, segment offset must always lie in the range = [0, 96-1] = [0, 95]

Now,

- Since generated segment offset lies in the above range, so request generated is valid.
- Therefore, no trap will be produced.
- Physical Address = 1952 + 95 = 2047

Thus, Option-(C) is correct.

To watch video solution and practice other problems,

**Next Article-** **Segmented Paging in OS**

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