Differences between version 4 and previous revision of FAT12.
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| Newer page: | version 4 | Last edited on Saturday, November 16, 2002 7:57:43 pm | by PerryLorier | Revert |
| Older page: | version 1 | Last edited on Saturday, November 16, 2002 6:17:03 pm | by PerryLorier | Revert |
@@ -1,9 +1,9 @@
FAT12 was Microsofts File system designed for floppies.
[FAT] is an acronym for __F__ile __A__llocation __T__able, which refers to the table which lists where on the disk files are stored.
-The reason it is called FAT12 is that each [Cluster
] is represented in the File Allocation Table by a 12 bit number. Some values:
+The reason it is called FAT12 is that each [DiskCluster
] is represented in the File Allocation Table by a 12 bit number. Some values:
|^__Value__|^__Meaning__
|>000|<The cluster is unused and available
|>FF7|<The cluster has a bad sector in it and will not be allocated
@@ -14,4 +14,8 @@
Note that FAT12 can only address up to 64mb in size, so [FAT16] was introduced.
FAT12 also has the 8.3 filename charactoristics.
+
+FAT12 uses a FirstFit method for finding which [DiskCluster] to allocate first. According to my "MS-DOS Operating System PRogrammer's Reference Manual" (for DOS 2.0!): "This permits the most efficient utilization[[sic] of disk space because clasters made available by erasing files can be allocated for new files." The problem of course of using FirstFit in this case is that file fragment a lot. Most other file systems try and spread the data around the disk so that when a file needs to be extended it has plenty of space that can be used.
+
+Defrag is a program that takes all the files on the disk and packs them to the beginning of the disk and defragmenting them. This tends to improve performance, at least for a while. After a few deletions and additions a disk that has been "packed" with defrag will show worse performance for new files. Sigh.
