Angus Duggan HDFS

Angus Duggan's HDFS shares the same basic file structure as Acorn's DFS.

Sector 1 byte 6 bit 3 is set for HDFS with but 2 clear for single-sided and set for double-sided disks.

HDFS subdirectories follow the same format as the main catalogue.

This is the structure of the catalogue header:

Byte	Track 0 Sector 0								Track 0 Sector 1
Byte	7	6	5	4	3	2	1	0	7	6	5	4	3	2	1	0
0	10Sect	First 8 characters of volume title padded with NULs or spaces								Last 4 characters of volume title padded with NULs or spaces
1
2
3
4									BCD catalogue cycle number
5									Number of files
6											Boot Opts		1	Sides	98
7									7	Sectors in volume						0
8	10Sect	File name padded with spaces							7	Load address						0	Last file
9	18Len								15	Load address						8
10									7	Execution address						0
11	IsDir								15	Execution address						8
12	Read								7	File length						0
13	Write								15	File length						8
14	Exec								17 16 Exec		17 16		17 16 Load		9 8
15	Lk.	Directory							7	Start sector						0
16	10Sect	File name padded with spaces							7	Load address						0	Second to last file
17	18Len								15	Load address						8
18									7	Execution address						0
19	IsDir								15	Execution address						8
20	Read								7	File length						0
21	Write								15	File length						8
22	Exec								17 16 Exec		17 16		17 16 Load		9 8
23	Lk.	Directory							7	Start sector						0

For the volume header, bytes 0…7 of both sectors:
- Track 0 sector 0 byte 0 bit 7 is bit 10 of the number of sectors in the volume.
- Track 0 sector 1 byte 6 bit 3 is set. Bit 2 is the number of sides-1, 0=single sided, 1=double sided.
For file entries:
- Sect is bit 10 of the start sector.
- Len is bit 18 of the file length.
- IsDir defines if the entry is a file or a subdirectory.
- If the Read, Write or Exec attributes are set then the file can not be read, written or executed respectively.
For a directory entry, the directory has the same layout as the main Catalog, except the volume title becomes the directory name^{[Citation needed]}.

This section is based loosely on the following:

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