A fast and easily customised operating system
for ARM devices
FileCore Disc Descriptor
Programmer's Reference Manuals
» Part 4 – Using Filing Systems
» FileCore
» Technical Details
» FileCore Disc Descriptor
FileCore Disc Descriptor
File Disc Descriptor (small Disc1)
| Offset | Name | Meaning |
|---|---|---|
| +0 | Log2Secsize | Log2 of sector size (Sector size = 2^x) |
| +1 | Secspertrack | Number of sectors per track |
| +2 | Heads | Number of disc heads, if interleaved otherwise -1 (1 for old directories) |
| +3 | Density | Disc density |
| +4 | IDlen | Length of id field of a map fragment (in bits) |
| +5 | Log2Bpmp | Log2 of number of bytes per map bits |
| +6 | Skew | Track to track sector skew for random access file allocation |
| +7 | Bootoption | Boot option (as in *Opt 4,n) |
| +8 | Lowsector | Lowest numbered sector + disc description flags |
| +9 | Nzones | Number of zones in the map |
| +A-B | Zone_Spare | Number of non-allocation bits between zones |
| +C-F | Root | Disc address of root directory |
| +10-13 | Disc_Size | Disc size in bytes |
| +14-15 | Disc_Id | Disc cycle ID |
| +16-1F | Disc_Name | Disc name (spaced to 10 chars, no terminator) |
| +20-23 | Disctype | Filetype given to disc |
| +24-3F | Reserved, must be 0 |
File Disc Descriptor (Large Disc2)
| Offset | Name | Meaning |
|---|---|---|
| +0 | Log2Secsize | Log2 of sector size (Sector size = 2^x) |
| +1 | Secspertrack | Number of sectors per track |
| +2 | Heads | Number of disc heads, if interleaved otherwise -1 (1 for old directories) |
| +3 | Density | Disc density |
| +4 | IDlen | Length of id field of a map fragment (in bits) |
| +5 | Log2Bpmp | Log2 of number of bytes per map bits |
| +6 | Skew | Track to track sector skew for random access file allocation |
| +7 | Bootoption | Boot option (as in *Opt 4,n) |
| +8 | Lowsector | Lowest numbered sector + disc description flags |
| +9 | Nzones | Number of zones in the map |
| +A-B | Zone_Spare | Number of non-allocation bits between zones |
| +C-F | Root | Disc address of root directory |
| +10-13 | Disc_Size | Disc size in bytes |
| +14-15 | Disc_Id | Disc cycle ID |
| +16-1F | Disc_Name | Disc name (spaced to 10 chars, no terminator) |
| +20-23 | Disctype | Filetype given to disc |
| +24-27 | Disc_size2 | High word of disc size |
| +28 | Share_size | Share Size Information |
| +29 | Big_flag | 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