Archival data storage is a system for keeping data stored for long periods of time, often more than a few years. The primary difficulty of archival data storage is that many forms of storage media degrade or fail over time, making it difficult to store electronic information for posterity.
Magnetic media is usually the cheapest and most convenient option for backing up data, but over 10 to 30 years, the magnetic fields that hold the bits of data fade. Hard drives may also suffer mechanical failure, potentially wiping out any data stored on the platters. Optical media has a longer shelf life, as much as 50 years for low-density discs like CDs, although physical damage, humidity, mold and other problems can render discs unreadable when stored improperly. Flash memory storage may only last 5 to 15 years before any stored data becomes unreadable.
In addition to the survival of the storage media, archival storage often runs into difficulties with data compatibility. Over time, file formats change, and data stored using abandoned standards may be difficult to retrieve. In some cases, the physical connections used to access storage media change, with older IDE hard drives becoming incompatible with SATA connectors in later models.