ALTERED CARBON WORLD OVERVIEW

Altered Carbon takes place in a far future where humans have discovered a means to keep the human consciousness on devices called "cortical stacks", which are small discs that implant into the spine at the back of the neck. This technology has opened up interstellar travel through the use of "needlecasting", where people are able to transfer their minds (referred to as Digital Human Freight or DHFs) instantaneously over huge distances into other bodies (called sleeves). However, it also means that a person can technically live forever, as long as their stack is not destroyed and they have the means to have it placed in a new sleeve.

All humans have stacks implanted when they are one year old, but for the lower classes being resleeved on death is not a guarantee and can come with a whole slew of problems, like being cross-sleeved (placed in a sleeve of the incorrect gender presentation). People can also choose not to be resleeved at all. As this is usually for religious reasons, this is referred to as "religious coding" and prevents a person being "spun back up" entirely.