Delete me: FileCore Disc Descriptor (Rev #3, changes)
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FileCore
» Technical Details
» FileCore Disc Descriptor
FileCore Disc Descriptor
File Disc Descriptor (small Disc1)
| Offset | Name | Meaning |
|---|---|---|
| +0 | Log2 of sector size (Sector size = 2^x) | |
| +1 | Number of sectors per track | |
| +2 | Number of disc heads, if interleaved otherwise -1 (1 for old directories) | |
| +3 | Disc density | |
| +4 | Length of id field of a map fragment (in bits) | |
| +5 | Log2 of number of bytes per map bits | |
| +6 | Track to track sector skew for random access file allocation | |
| +7 | Boot option (as in |
|
| +8 | Lowest numbered sector + disc description flags | |
| +9 | Number of zones in the map | |
| +A-B | Number of non-allocation bits between zones | |
| +C-F | Disc address of root directory | |
| +10-13 | Disc size in bytes | |
| +14-15 | Disc cycle ID | |
| +16-1F | Disc name (spaced to 10 chars, no terminator) | |
| +20-23 | Filetype given to disc | |
| +24-3F | Reserved, must be 0 |
File Disc Descriptor (Large Disc2)
| Offset | Name | Meaning |
|---|---|---|
| +0 | Log2 of sector size (Sector size = 2^x) | |
| +1 | Number of sectors per track | |
| +2 | Number of disc heads, if interleaved otherwise -1 (1 for old directories) | |
| +3 | Disc density | |
| +4 | Length of id field of a map fragment (in bits) | |
| +5 | Log2 of number of bytes per map bits | |
| +6 | Track to track sector skew for random access file allocation | |
| +7 | Boot option (as in |
|
| +8 | Lowest numbered sector + disc description flags | |
| +9 | Number of zones in the map | |
| +A-B | Number of non-allocation bits between zones | |
| +C-F | Disc address of root directory | |
| +10-13 | Disc size in bytes | |
| +14-15 | Disc cycle ID | |
| +16-1F | Disc name (spaced to 10 chars, no terminator) | |
| +20-23 | Filetype given to disc | |
| +24-27 | High word of disc size | |
| +28 | Share Size Information | |
| +29 | Big Flag | |
| +2A-3F | Reserved, must be 0 |
Disc Description Flags
| Bits | Meaning |
|---|---|
| 0 – 5 | Lowest numbered sector id on a track |
| 6 | Treat sides as a sequence (not interleaved), if set |
| 7 | Disc is 40 track, if set |
Share Size Information
| Bits | Meaning |
|---|---|
| 0 – 3 | Log2 share size granularity (in sectors) |
| 4 – 7 | Reserved, must be zero |
Big Flag
| Bits | Meaning |
|---|---|
| 0 | Identified as ‘Large’ disc, if set |
| 1 – 7 | Reserved, must be zero |
Disc Densities
| # | Meaning |
|---|---|
| 0 | Hard disc |
| 1 | Single density (125 Kbps FM) |
| 2 | Double density (250 kbps FM) |
| 3 | Double density (300 kbps FM), i.e. higher rotation speed DD |
| 4 | Quad density (500 kbps FM) |
| 8 | Octal density (1000 kbps FM) |
Notes
There are two different FileCore Disc descriptor formats. The earlier version only supports small hard discs, while the later version supports larger discs.
1 Small disc are returned on versions prior to RISC OS 3.60
2 Large discs are returned on RISC OS 3.60 and later
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