The different possibilities have been explored in familiar fiction and can be nested neatly in order of their descending “humanness.”

The Wizard of Oz. HAL isn’t a computer at all. He is actually an ordinary flesh-and-blood man hiding behind a techno-facade-the ultimate homun­culus, pushing buttons with ordinary fingers, pulling levers with ordinary hands, looking at internal screens and listening to internal alarm buzzers. (A variation on this theme is John Searle’s busy-fingered hand-simulation of the Chinese Room by following billions of instructions written on slips of paper.)

William (from “William and Mary,” in “Kiss Kiss” by Roald Dahl). HAL is a human brain kept alive in a “vat” by a life-support system and detached from its former body, in which it acquired a lifetime of human memory, hankerings, attitudes, and so forth. It is now harnessed to huge banks of prosthetic sense organs and effectors. (A variation on this theme is poor Yorick, the brain in a vat, in the story “Where Am I?” in my “Brainstorms.“)

Robocop, disembodied and living in a “vat.” Robocop is part-human brain, part computer. After a gruesome accident, the brain part (vehicle of some of the memory and personal identity, one gathers, of the flesh-and-blood cop who was Robocop’s youth) was reembodied with robotic arms and legs, but also (apparently) partly replaced or enhanced with special-purpose software and computer hardware. We can imagine that HAL spent some transitional time as Robocop before becoming a limbless agent.