that archive transfer will become a continuous, never-ending process. Digital rights management Maintaining digital information in an accurate and accessible format over an extended retention period also must address the requirements of the authors' digital rights. In many cases, the data may include proprietary information that should not be accessible to all, but only to a defined group of users who understand or have legally agreed to only utilize the information in limited ways so as to protect the proprietary rights of the original authoring team. Maintaining this requirement over decades can be a challenge that requires processes and tools to ensure total compliance. Reproducibility Digital information must be able to be reproduced as originally intended or available. This is significant especially where the original data was produced on technology at a lower level than currently possible. For example, archivists try to maintain the distinction between listening to a gramophone record played on a gramophone as opposed to a digitally cleaned version of the same recording through a modern hi-fi system. Given that individuals' personal data has been growing at a rapid rate in the 21st century, these archiving issues affecting professional repositories will soon be manifest in small organisations and even the home. Types of storage Solid-state memory devices Digital computers, in particular, make use of two forms of memory known as RAM or ROM and although the most common form today is RAM, designed to retain data while the computer is powered on, this was not always the case. Nor is active memory the only form used; passive memory devices are now in common use in digital cameras. Magnetic, or ferrite core, data retention is dependent on the magnetic properties of iron and its compounds. PROM, or programmable read-only memory, stores data in a fixed form during the manufacturing process, with data retention dependent on the life expectancy of the device itself. EPROM, or erasable programmable read-only memory, is similar to PROM but can be cleared by exposure to ultraviolet light. EEPROM, or electrically erasable programmable read-only memory, is the format used by flash memory devices and can be erased and rewritten electronically. These devices tend to be extraordinarily resilient; in a 2005 destructive test, a USB key survived boiling in a custard pie, being run-over by a truck and fired from a mortar at a brick wall. Although physically damaged after the final test, some deft soldering