5 Comments In the last week’s part 1 of my FAT and SD tutorial, we got as far as reading the file entries in root directory, and peeking into a file with hex editor. Now we’ll cover the file allocation table itself to enable reading longer files, and adapt the code into a small footprint FAT16 library!
File allocation table in FAT16
In the previous part, we learned that the data on a FAT-formatted disk is stored in clusters. In our test image, the cluster size was 32 sectors, i.e. 16 kiB (16 384 bytes). Let’s imagine a newly formatted disk with 100 free clusters, with the clusters numbered from 2 (the first cluster at the beginning of data area) to 101 (the very last cluster). Now let’s copy some files there:
| File operation | File allocation |
|---|---|
| Copy HAMLET.TXT (193 082 bytes) to disk | Clusters 2-13 allocated for the file (196 608 bytes) |
| Copy README.TXT (353 bytes) to disk | Cluster 14 allocated for the file |
| Create SUBDIR on disk | Cluster 15 allocated for the directory file entries |
| Create 1.TXT in SUBDIR | Cluster 16 allocated for the file, a new file entry written to SUBDIR (beginning of cluster 15) |
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