Question

4) If the partitions are fixed and a new job arrives requiring 52 blocks of
main memory, show memory after using each of the following partition
selection approaches.
a) First fit
b) Best fit
c) Worst fit
operating system
process 1
Empty 60 blocks
process 2
process 3
Empty 52 blocks
Empty 100 blocks

Answer 1

To visualize how memory will be allocated for a new job requiring 52 blocks of main memory using different partition selection approaches, let’s assume we have the following partitions:

- Partition 1: 60 blocks (Empty)
- Partition 2: 52 blocks (Empty)
- Partition 3: 100 blocks (Empty)

Now, let’s analyze each memory allocation approach:

### a) First Fit
**First Fit** allocates the first block of memory that is large enough to satisfy the request.

1. The job requires **52 blocks**.
2. We check the partitions in order:
- Partition 1 (60 blocks): **Fits** (Allocated here)
- Partition 2 (52 blocks): Not checked, as the job has already been allocated.

After using the **First Fit** method, the memory layout will be:
```
Partition 1: Process 1 (52 blocks allocated)
Partition 1: Empty (8 blocks remaining)
Partition 2: Empty (52 blocks)
Partition 3: Empty (100 blocks)
```

### b) Best Fit
**Best Fit** allocates the smallest available partition that is large enough to satisfy the request.

1. The job requires **52 blocks**.
2. We check the available partitions:
- Partition 1 (60 blocks): Can accommodate the request.
- Partition 2 (52 blocks): Exactly matches the request.
- Partition 3 (100 blocks): Can accommodate the request.
3. **Best Fit** chooses Partition 2 since it has the exact size.

After using the **Best Fit** method, the memory layout will be:
```
Partition 1: Empty (60 blocks)
Partition 2: Process 1 (52 blocks allocated)
Partition 2: Empty (0 blocks remaining)
Partition 3: Empty (100 blocks)
```

### c) Worst Fit
**Worst Fit** allocates the largest available partition to satisfy the request.

1. The job requires **52 blocks**.
2. We check the available partitions:
- Partition 1 (60 blocks): Can accommodate the request.
- Partition 2 (52 blocks): Can accommodate the request.
- Partition 3 (100 blocks): Can accommodate the request.
3. **Worst Fit** chooses Partition 3 since it has the largest size.

After using the **Worst Fit** method, the memory layout will be:
```
Partition 1: Empty (60 blocks)
Partition 2: Empty (52 blocks)
Partition 3: Process 1 (52 blocks allocated)
Partition 3: Empty (48 blocks remaining)
```

### Summary:
- **First Fit** allocates to Partition 1, leaving 8 blocks remaining in that partition.
- **Best Fit** allocates to Partition 2, leaving that partition fully occupied.
- **Worst Fit** allocates to Partition 3, leaving 48 blocks remaining in that partition.