What is the difference between a preservation master copy and an access copy, and why do archives keep both?

When archives digitize or capture records, they typically create more than one version of each file. Two of the most important are the preservation master copy and the access copy. They serve different purposes, and keeping both is a deliberate strategy for protecting records over the long term while still making them usable.

The preservation master copy

The preservation master (sometimes called the archival master) is the highest-quality, most faithful version of a record. It is created to capture as much detail as possible and to last for decades or longer.

Key characteristics:

• High fidelity — captured at high resolution, with full color or tonal depth, to preserve detail that may be needed in the future.
• Uncompressed or losslessly compressed — avoids the quality loss that comes from discarding data, so nothing is permanently degraded.
• Stable, well-documented formats — favored because they are widely supported and likely to remain readable.
• Restricted handling — the master is stored securely and rarely touched, reducing the risk of accidental change or loss.

The master is the authoritative source from which other versions are made. If a future need arises, archivists can return to it.

The access copy

The access copy is a smaller, more convenient version made from the master, intended for everyday use by researchers and the public.

Key characteristics:

• Smaller file size — compressed and lower in resolution so it loads quickly and streams or downloads easily.
• Common, user-friendly formats — opens in ordinary software and browsers.
• Freely handled — viewed, copied, and shared without endangering the original.

Why archives keep both

The two-copy model separates preservation from use:

• The master safeguards authenticity and quality for the long term, even as technology and formats change.
• The access copy meets immediate demand without exposing the master to wear, accidental edits, or loss.
• If an access copy is damaged, lost, or needs to be remade in a new format, the master remains the trusted source for regeneration.

This approach reflects established digital preservation and digitization practice. For more on capture standards, see the FADGI digitization guidelines and the Library of Congress digital preservation resources, and explore related material on the archives and preservation hub.