Gradual uploading is a process where the mind of a biological sophont is incrementally transferred from a biological to an electronic substrate.
Before destructive uploading was developed, a form of partial, imperfect gradual uploading emerged in the Interplanetary Age. The widespread use of external hardware and software connected directly and indirectly to the user's brain allowed a slow transfer of consciousness out of the biological substrate and into external databases.
This technology allowed the user to "outsource" much of eir mentality and memory storage to external substrates which were separate from the sophont's own brain, until finally most of the sophont's thoughts, perceptions, memories, identity, etc. take place outside and away from the mass of grey matter the sophont initially came equipped with. Early attempts at gradual uploading into an exoself were made during the 250s. Even in the Current Era some bionts choose to upload in this fashion.
The external hardware which gradually comes to hold more and more of the individual's personality is known as the exocortex, while the software which runs on this equipment is known as the Exoself.
It is possible to copy most of a biont's extended consciousness by this method, since many of the most competent processes of intellection now occur outside the skull in the exocortex. As with most evolutionary processes, it is difficult to tell exactly where one entity ended and another began. Algorithms within the exocortex model the biological mind of the user quite efficiently, and from all this information a reasonably good emulation of the original biont's mind can be reconstructed.
In the current era, the use of transapientech reconstruction techniques means that the resulting emulation can be remarkably accurate.
Gradual neuron replacement
A reasonably advanced form of destructive uploading which was developed during the Nanotech Age of Old Earth; the first successful uploads of this kind were achieved in 330 A.T..
Gradual neuron replacement occurs over a prolonged period of time, as the individual neurons of the sophont's mind are replaced one by one by functionally-equivalent devices. The brain continues to operate throughout the process, and if carried out correctly, the subject will experience no discontinuity as eir brain slowly becomes replaced by electronic components.
Early attempts at gradual uploading required the sophont's skull to be removed almost completely, as the artificial neuron replacement devices were larger than biological neurons and required active cooling; during the replacement process the brain would become considerably larger in size than before. Later refinements of the process allowed the uploading to occur entirely within the skull, so that the sophont remained unchanged externally but now had an electronic brain inside the skull. Such hybrid beings were sometimes called Changelings, and were often the subject of distrust and discrimination.
Eventually the technology for non-destructive uploading was developed, a process where the neurons are scanned in-situ by nanoscale probes and the information content replicated elsewhere. However gradual neuron replacement is still practiced in a number of independent polities, especially in the Outer Volumes.