Notes on Hardware
Disks
Disk structures
Unlike *X systems and Windows, OpenVMS does not require specific 'formatting' of a disk. It uses tha basic, low-level formatting that is present on ANY disk. That's why there is no FORMAT command - the disks are already formatted....OpenVMS uses the OnDiskStructure - hence: ODS. INITIALIZE however, is needed. There is a number of administrative files and areas that need to be prepared. Most notable are 000000.DIR - the root directory of the disk, and INDEXF.SYS: the master file directory, that holds attribute- and access data for every file on disk. There are more required files, all used by specific OpenVMS functionality that is normally used by layers and components in the OS. It's here that the major differences are handled, and NOT on the disk itself. The orginal system was, obviously, named ODS-1. It had huge limitations, to today's standards: Filenames were limietd to 8 characters, the file extension to 3. Theer was no, or a very limited directory-structure. This structure was introduced on the PDP under RSX - and today's RMS still bears quite some marks of it's 16-bit history.... ODS-2, the next phase, introduced mych longer filenames and extensions: bouth could hold 39 characters, but limited to A..Z, 0..9, "$", "-" and "_". Directory-depth was originally limited to 8 but in later days this limitation was lifted. The latest leave on the tree is ODS-5. Physically the same as ODS-2, but it allows filenames up to 255 characters, upper and lowercase characters, and all those that ODS-2 did not accept - though 'escaped' by the caret ("^") in display - you dont have to type them to access a file. Just the special characters "*"and "?" cannot be used. These are used to mark wildcards.
Modern packages can sometimes be installed on ODS-2 disks, their naming convention should adhere to it's limitations: Names consisting of the limited (uppercase) characterset, within a 39.39 format. But most packages require the "modern" characterset: All but a few characters allowed; multiple dot, even in a directory name; mixed case... This means it can only be sored on an ODS-5 disk.
To be able to use these facilities, your process needs the EXTENDED parse-style. Some logicals couild be needed as well.
Moving from OS-2 to ODS-5 is simple, but requires the disk to be mounted privately. Moving the other way round is far more work: it can only be achieved by backup and restore, and could cause problems.