Folio, one fold

Folio assumes a Linux host with a real filesystem and memory mapping. The artefact is mapped rather than loaded, so resident memory stays small while the whole index remains addressable. Mean fanout is 2.60, so a lookup is one to three reads.

This is the format for a server, a workstation, or an appliance with a disk. If your target has a disk and an MMU, there is no reason to run anything smaller.

Because storage is not the binding constraint, fingerprints run at full width and the silent false accept rate stops being a design consideration. Every other format is a negotiation with that number; Folio is not.

A printer’s folio is a sheet folded once: the largest page you can make from the stock. The metaphor is load-bearing rather than decorative. A fold is a physical constraint on a sheet, not a grade of quality, and the format names the hardware floor rather than the competence.