Segmentation in OS | Practice Problems

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?

1. 0, 430
2. 1, 11
3. 2, 100
4. 3, 425
5. 4, 95

 

Calculate the physical address if no trap is produced.

 

Solution-

 

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

1. Segment Number
2. 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,

Watch this Video Lecture

 

Next Article- Segmented Paging in OS

 

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