Software Security The following question involves the following Table 5.6, which

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Software Security

The following question involves the following Table 5.6, which contains part of a File Allocation Table. The “Cluster” column contains cluster numbers; the “Pointer” column contains the corre­sponding FAT entry.

The FAT entry contains one of the following: 0 to indicate a free cluster, 9999 to indicate the end of file, and any value in between indicates the next cluster in the file.

The following directory entries apply to these FAT entries:

-    Name: F1, Starting Cluster: 100

-    Name: F2, Starting Cluster: 106

-    Name: F3, Starting Cluster: 120

-    Name: F4, Starting Cluster: 126

Table 5.6: Part of a file allocation table:

2) For each file listed above, give the number of clusters in the file.

Cluster PointerClusterPointerCluster Pointer 100 10I 102 103 104 105 110 10I 102 103 104 105 106 120 121 122 123 124 121 122 123 124 112 112 113 114 115 116 113 125 107 108 109 116 126 107 108 109 127 128 129 110 118 127 128 129 118 119 119

Explanation / Answer

In above Table Cluster and pointers are given. We know Poiinter column specify the Empty Cluster i.e. 0, End of File 9999 and cluster number for prsence of cluster in the file.

Now We have four files each file contains the starting cluster and we have to find the number of cluster in the file. To find the number of cluster we need to track the starting cluster to next pointer (cluster) until we reached to end of file.

Now File F1 starts from Cluster 100 so we need to start by finding the next cluster number

It traversed as 100 -> 101, 101->102, 102->103, 103->104, 104 -> 105, 105 -> 9999(end of file) So there are 5 Cluster in the file F1.

Similarly File F2 can be traversed, which starts from Cluster 106

106->107, 107->108 ,108->109, 109->116, 116->119, 119-> 9999 (End of File) thus in this file there are 5 Clusters in F2

In same manner we can find the number of cluster in file F3 and F4.

F3 start with cluster 120 so we can traverse it as

120->121,121->122,122->123,123->124, 124->9999 (End of File) thus in this file there are 4 Clusters.

F4 start with cluster 126 so we can traverse it as

126->127, 127->128,128->129,129->110, 110->111, 111->112, 112->113, 113->9999 (End of File)

Hence in this file there are 7 Clusters.

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