The original note, as written at the time
In order to store information digitally for retrieval several years ahead you need first and foremost to document the way the technology works and how to build a machine that can read the digital storage device you are creating. This documentation should be primarily stored in a physical form — preferably a book and a set of stone tablets, maybe etchings in concrete. After this, the storage device can be created.
Ongoing development
To store information digitally for retrieval several years ahead, you must first document how the technology works and how to build a machine that can read the storage device you are creating. That documentation should be primarily physical — preferably a book, and a set of stone tablets, or etchings in concrete. Only then is the storage device made.
This is the most far-sighted idea in the whole collection and almost nobody does it.
The archive question is usually framed as durability: will the bits survive. The real question is legibility: will anyone, in fifty or a hundred years, be able to read them. A perfectly preserved disk with no drive, no file system specification and no schematic is a very durable object with no information in it.
So the specification must be stored in a medium that requires no technology to read. Paper first, because paper is readable with the eye and there is a great deal of it, and because a book survives neglect better than most people think. Stone or concrete second, because the failure mode of paper is fire and the failure mode of concrete is time, and those are different risks.
The order matters more than the choice. Document first, then build the device. If you build first, you will write the documentation from memory afterwards, and you will write the things you know rather than the things a stranger needs. Every great software project has learned this and every great software project has learned it too late.
And the document must assume ignorance, not intelligence. Not “use the standard reader” but a schematic, a parts list, and a description of what the machine is for. The reader should be assumed to be a competent person with no context, which is the most likely and the most useful assumption.
Civilisations are not remembered by their storage. They are remembered by their instructions.