All numbers are little-endian. All references to KB, MB, TB, GB, PB, EB, etc. refer to power-of-2 numbers because I am a programmer and I don’t like *iB.
What good is a filesystem without a partition on which to store it? The OCGPT (for OpenComputers General Partition Table) partition table spans sectors 2-9 of the disk and supports up to 56 partitions. A disk may be up to 8 EB in size.
+------------------------------------------------+
| OCGPT Superblock Format |
+------------------------------------------------+
| Bytes | Description |
+------------------------------------------------+
| 1-8 | Signature - '\27[OCGPTm'. Modeled |
| | after a VT100 escape code. |
+------------------------------------------------+
| 9-16 | Size of the bootloader contained after|
| | sector 9, in sectors. 0 for OCUEFI |
| | disks. |
+------------------------------------------------+
| 17-512 | Unused. A use may be found |
| | eventually. |
+------------------------------------------------+
+------------------------------------------------+
| OCGPT Partition Table Format |
+-------+----------------------------------------+
| Bytes | Description |
+-------+----------------------------------------+
| | Type of the filesystem the partition |
| 1 | contains. See RESERVED PARTITION TYPES |
| | below. |
+-------+----------------------------------------+
| 2-4 | Partition flags. See PARTITION FLAGS. |
+-------+----------------------------------------+
| | Partition GUID - 8-byte string, each |
| 5-12 | character ranging from 0-255. Randomly |
| | generated on partition creation. |
+-------+----------------------------------------+
| | Partition label, 36 bytes. If not |
| 13-48 | specified, should be a UUID similar to |
| | components. |
+-------+----------------------------------------+
| 49-56 | Partition starting sector, 8 bytes for |
| | future proofing. |
+-------+----------------------------------------+
| 57-64 | Partitioon ending sector, 8 bytes. |
+-------+----------------------------------------+
Unrecognized partition types should be ignored.
Request a filesystem reservation and I’ll add it here. Otherwise, your filesystem may not be correctly recognized!
+------------------------------------------------+
| Reserved Partition Types |
+-------+----------------------------------------+
| ID | Filesystem Name |
+-------+----------------------------------------+
| 0x01 | OCFS |
+-------+----------------------------------------+
| 0x02 | OpenFS |
+-------+----------------------------------------+
| 0x03 | FoxFS |
+-------+----------------------------------------+
| 0x04 | ZebraFS |
+-------+----------------------------------------+
| 0x05 | NitroFS |
+-------+----------------------------------------+
| 0x06 | BROFS |
+-------+----------------------------------------+
These flags hold information about the partition.
+------------------------------------------------+
| Partition Flags |
+-------+----------------------------------------+
| Flag | Meaning |
+-------+----------------------------------------+
| 0x01 | The partition is bootable. |
+-------+----------------------------------------+
| 0x02 | The partition should emulate a managed |
| | filesystem. |
+-------+----------------------------------------+
| 0x04 | The BIOS, if following OCUEFI, should |
| | load bootloader.lua from this |
| | partition. Only guaranteed to be valid |
| | for BROFS as many other filesystems |
| | are too complex to reasonably fit their |
| | drivers into an EEPROM. |
+-------+----------------------------------------+
The BIOS should load and execute the first 512 bytes of the disk as the stage one bootloader. If the disk is NOT bootable, this should simply display the text Non-System Disk or Disk Error., wait for a keypress, and restart. If the disk IS bootable, the boot loader should load and execute sectors 10 through 32 of the disk.
The stage two boot loader should be stored between sectors 10 and 32 of the disk - a total of 11 KB of space. The rest of the disk should be dedicated to partitions.
The recommended filesystem for storage of bootloader data, such as filesystem drivers, is the Bootloader Read-Only File System documented here.
OCGPT provides a method for booting disks using a method similar to EFI: OCUEFI, or the OpenComputers Unmanaged Extensible Firmware Interface.
Given the simplicity of BROFS, a basic read-only driver can be implemented in a very small space such as an EEPROM. The BIOS stored in EEPROM may load a boot script as bootloader.lua from the BROFS partition to act as the bootloader, rather than the bootloader being stored as raw data on the disk.
OCUEFI bootloaders differ slightly from BIOS-style bootloaders.
On initialization, an OCUEFI bootloader should parse the OCGPT and load any necessary drivers from the BROFS partition. If applicable, the bootloader should present a menu for selection of a boot device; if not applicable, the bootloader should either proceed to boot from the configured partition, display a panic message, or present a command line.