Memory orbs are pre-War magical archano-tech devices used to store a pony's memories.
A complete list of all discovered memory orbs, as well as other similar recordings, can be found on the List of Recordings.
Memories are stored within the orb, and upon access, are relived in their fullest, letting the spectator experience the whole range of senses the host had produced, whilst still retaining their own conscience. The spectator feels as if they are host's body, and doing its actions. The spectator becomes unaware of their own body and their surroundings outside of the memory for its duration.
Damaged memory orbs can lead to warped, extreme, and often painful, sensory experiences.
In order to access a memory, the spectator would need to focus their magic upon the orb; it matters little what type of magic is used, though telekinesis is the most common. Due to its magical nature, only unicorns and Alicorns are able to access the memories within an orb unassisted.
Memories can be of any length, from few seconds to whole days, and the time spent viewing the memory is always the same length as the duration of the memory itself.
In order to place a memory inside of a memory orb, the memories must be extracted from the mind of a pony. This can be done in a manner that either completely removes or copies the memories from the mind of the subject.
Most historical extractions of memories have been forceful, and this was a commonly-used technique by the information-seeking agents of the Ministry of Morale against Zebras and potential Zebra Sympathizers. Littlepip voluntarily had memories removed to hide them from the Goddess, while Calamity asked to have a large amount of memories copied to be forcefully shown to the Shadowbolts.
Black opals are a unique type of memory orb that can be used to store memories recorded by recollectors. They can be accessed using a recollector or, like memory orbs, through the focus of magic.
In Other Stories
In the side story Project Horizons, some memory orbs have built in protection spells, requiring the pony attempting to view the memory to utilize a 'password'. This entails thinking of the proper thing while attempting to access the orb, failure can result in a number of negative effects, up to and including death as Goldenblood's memories were so protected.
According to the side-story the Memory-orbs were designed by a student named Spellfield 50 years before the war. They were commissioned by an organization, who promised him a lot of money for the Memory-orbs. When he realized that they can be used for ethically dubious (invasion of personal space of unwilling spell-targets) or even illegal purposes (torture by removing memories) he refused the money as long as they destroy any paper-trail linking him to them.
A Memorhedron is a tetrahedron-shaped device compatible with most terminals (like PipBucks). It can store multiple memories and plays them in the order they were inserted. Considering how long the last memory lasted, it needs to be recharged longer. It is able to safely play a Memory when the Memorhedron is not fully charged at the cost of parts of the Memory.