FileCore Disc Addresses (changes)
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FileCore
» Technical Details
» Disc Addresses
Disc Addresses
Definitions used
| Term | Meaning |
|---|---|
| object | Used to define a single file or a directory |
| disc object | Used to define a logical group of fragments on a new map disc, that may contain one or more objects |
Types of Disc Addressing
There are two different types of disc address that FileCore currently uses. They are:
| Type | Description |
|---|---|
| Physical | Uses actual physical address disc address of the disc, using |
| Internal | Used by new map discs, |
Physical Disc Addresses
Because Physical Disc Addressing uses an offset given in bytes sectors from the start of the disc to determine the disc address to read/write. To calculate the physical disc address of a byte you need the know several pieces information about the disc. They are:
| Identifier | Description |
|---|---|
| h | Head number |
| t | Track number |
| s | Sector number |
| b | Number of bytes into the sector |
| H | Number of heads on the Drive |
| S | Number of sectors per track |
| b | Number of bytes per sector |
| x | Number of defective sectors earlier on the disc. Note: only applicable for old map hard discs. Use zero for old map floppy discs or new map discs |
Calculating Physical Disc Addresses
Address = ((t × H × h) × S + s – x) × B + b
Tracks, heads and sectors are all counted from zero.
This formula can be used for any disc format (except an L-format one).
Internal Disc Addresses
Internal disc addresses are not used by the old disc map, only new map discs. An object's internal disc address is in the following binary form:
ddd00000 0fffffff ffffffff ssssssss
| Identifier | Description |
|---|---|
| ddd | Disc number (not used outside of FileCore itself) |
| fffffff ffffffff | Fragment Id |
| ssssssss | Offset within the object in units of 2share_size. Where share_size comes from the large disc record. |
You must ensure that if you format a disc, share_size is sufficiently large for the following to be true:
smallest fragment size ≤ (254 × 2log2secsize × 2share_size)
This ensures that FileCore can then share all the space within a shared disc object.
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