# Directory Track

Directory track 18

The directory track is contained totally on track 18. Sectors 1…18 contain the directory entries whilst sector 0 contains the BAM (Block Availability Map) and disk name/ID.

Since the directory is only 18 sectors large (19 less one for the BAM), and each sector can contain only 8 entries (32 bytes per entry), the maximum number of directory entries is 18 * 8 = 144.

The first directory sector is always 18/1, even though the t/s pointer at 18/0 (first two bytes) might point somewhere else.

It then follows the same chain structure as a normal file, using a sector interleave of 3. This makes the chain links go 18/1, 18/4, 18/7 etc.

Byte Content
7 6 5 4 3 2 1 0
00 15 Location of next directory sector, 0x0000=end 8 First Directory entry
01 7 0
02 Closed Locked Save 30File Type
03 15 Location of first sector of file 8
04 7 0
05 Filename in PETASCII padded with 0xA0
06
07
08
09
0A
0B
0C
0D
0E
0F
10
11
12
13
14
15 15 Location of first side-sector block 8
16 7 0
17 REL file record length, max value 254
18 Unused in CBM DOS, GEOS only
19
1A
1B
1C
1D
1E 7 File size in sectors 0
1F 15 8
20 Must be set to 0x0000 Second Directory entry
21
22 Closed Locked Save 30File Type
23 15 Location of first sector of file 8
24 7 0
25 Filename in PETASCII padded with 0xA0
26
27
28
29
2A
2B
2C
2D
2E
2F
30
31
32
33
34
35 15 Location of first side-sector block 8
36 7 0
37 REL file record length, max value 254
38 Unused in CBM DOS, GEOS only
39
3A
3B
3C
3D
3E 7 File size in sectors 0
3F 15 8

### Sector pointers

The sector pointers at offset 0x00, 0x03 & 0x15 are Track/Sector values.

The track number is in the first byte, sector number in the second.

#### Next directory sector pointer

The next directory sector pointer at offset 0 points to the next directory sector in the chain. If it's the last entry in the chain then it is set to 0x0000.

It is only valid for the first directory entry. On file entries other than the first one in the sector this pointer is unused & is set to 0x0000.

### File Type

7 3 2 1 0 Name File Type
00000Scratched, deleted file entry
10000DELDeleted
10001SEQSequential
10010PRGProgram
10011USRUser
10100RELRel

All other values are illegal and will produce strange results.

Some routines use all 4 lower bits, some ignore bit 3.

All file types require the Closed flag (bit 7) to be set. Only DEL is valid with Closed cleared when it indicates a deleted file entry.

### File length

The file length is a little endian value with the lsb first, msb last. It is a sector count, not the file count.

### REL files

Bytes with offset 0x15…0x17 are only used for REL files.

Last modified November 1, 2021: Add GEOS extensions (5b03c67)