Atari ST series Technical Reference Manual page 122

Table 6-2. Format for Directory Entry
Bytes
0-7 Eight-character primary name (ASCII text) (if file is deleted,
first character is $E5)
8-10 Three-character extension (ASCII text)
11 Attribute byte, contains following bit flags
Bit 0 = read-only file (can't be deleted or written to)
Bit 1 = hidden file (excluded from normal directory
Bit 2 = system file (excluded from normal directory
Bit 3 = volume label (can only exist in root)
Bit 4 = subdirectory
Bit 5 = archive bit
Bit 6 = reserved
Bit 7 = reserved
12-21 Reserved for future use
22-23 Date of creation
Bits 0-4 = Day of month (1-31)
Bits 5-8 = Month (1-12)
Bits 9-15 = Year (-1980)
24-25 Time of creation
Bits 0-4 = Seconds divided by 2 (0-29)
Bits 5-10 = Minutes (0-59)
Bits 11-15 = Hours (0-23)
26-27 Starting cluster number (in 8088 order, low-byte first)
28-31 File length in bytes (in 8088 order, low-byte first)
Subdirectories are structured as files that contain direc­
tory entries. Since these files may expand in size like any
other data files, there is no limit to the number of entries in a
subdirectory, as there is with the root directory. The first two
entries in a subdirectory are always dot ( . ), which stands
for the current directory and dot-dot ( .. ), whose entry
points to the first cluster in the parent directory (or is 0 if the
parent is the root directory).
File Allocation Tables (FATs)
The last internal data structure used by GEMDOS is known
as the File Allocation Table, or FAT. The FAT is used to keep
track of which clusters belong to which file. The system
works like this: For each cluster on the disk, there's a corre­
sponding FAT entry. The directory entry for each file con-
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CHAPTER 6
Contents
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