Extended Cortical Stack
Cortical Stack with more memory for multiple backups
A somewhat larger cortical stack with enough memory to accommodate multiple (usually 3) time-lapsed backups of an ego. By default, set to keep a 10 minute old and a 1 hour old ego image in addition to the instantaneous backup. These values can be changed at purchase/installation of the stack but not afterwards (in order to preserve security of the stack). The stack does not have enough memory to keep any backup greater than 6 hours old.
When resleeving from the cortial stack any of the three ego images can be used, usually as specified by the backup contract (although Firewall may interrogate forks of each image before resleeving and choose the one they think is appropriate). If a time-lapse image is chosen there is a +2 Continuity Stress modifier due to the fact that the character does not have memory of how they died. This may be increased by the GM if the time-lapse ego image is aware of their imminent death.
Extending the memory of a cortical stack adds 50% to the cost. This also applies to upgrades like the Emergency Farcaster because the extra data requires more antimatter to transmit.
Extended cortical stacks are popular with sentinels who might not want to remember their death, but still want to remember the mission, choosing to resleeve with the 10 minute or 1 hour backup to maintain most of their memories. Another clever use is as a backup failsafe if infected by the Exsurgent virus, hit by a basilisk hack, or even overcome by mental trauma. In these cases irreversible mental damage would force a resleeve from a pre-mission backup. However, if caught in time, the sentinel can terminate themselves; the instantaneous backup would be infected but hopefully one of the time-lapsed images would not yet have been affected. Firewall encourages the use of extended cortical stacks, although cynical sentinels believe it is only so they can choose which backup to resleeve from, giving Firewall more control over the memories of its agents.
Extended cortical stacks work by taking a baseline ego image at a rate determined by the longest time-lapse setting and then tracking changes from that image (as determined by the instantaneous imaging) to maintain the time-lapse images. This means that really the stack contains information about the ego from the present back to the most recent baseline image (usually a 1 hour range). However, this information is heavily compressed and it is not recommended to try to reconstruct the ego corresponding to a time other than those stored by the stabilized ego images.