Hardware for Uploading

The "strong" uploading position is that the mind is simply an information processor, equivalent to a Turing machine in principle (though highly parallel). If this is true, then any computer with sufficient speed and capacity can implement the mind of an uploaded person. Of course, the speed and capacity of current hardware is far below what is required, and typically more exotic components (optical or molecular) are imagined. Nonetheless, in principle even a personal computer (or a Turing machine made of tissue paper!) could support an upload if it is given sufficient storage capacity, and if one is sufficiently patient.

The "weak" uploader asserts merely that the mind can be supported by an aritificial device, but makes no assertions about the nature of that device. It may, for example, require quantum interactions and nonlocal effects which cannot be implemented in a Turing-equivalent machine. The device may have to be geometrically similar to a real brain, or have components which respond to magnetic fields, or whatever. Robert Ettinger gives a commentary on this issue in which he argues that such nonsymbolic processes are necessary for generating our subjective consciousness.

In either case, no one actually supposes that an upload would be implemented on anything resembling today's computers. The speed and storage capacity required are simply too vast. Some developments which may prove relevant include:

• Protein-Based Computers. Recent work with bacteriorhodopsin, a light-sensitive bacterial protein, has been applied to optical data storage and computing. Cubes of material can theoretically store nearly 100 trillion bits per cubic centimeter (compared to about 100 million bits per cm^2 in two-dimensional media). Furthermore, this data can be read, written, and acted on in a highly parallel manner. For an excellent introduction, see the recent Scientific American article (Birge 1995).
• Nanocomputers. In Nanosystems, Drexler describes the molecular equivalent of simple mechanical computers, with switches implemented by interacting rods and knobs. With conservative assumptions, he estimates a switch density of roughly 15 trillion switches per cubic centimeter in a CPU with a 1 GHz clock speed, processing about a billion instructions per second (1000 MIPS).
• Optical Computers. Certain materials change their optical properties based on the light passing through them; that is, light changes the way they affect light. This allows us to build optical equivalents of transistors, the basic component of computers. In principle, an optical computer might be smaller and faster than an electronic one. But the chief advantage is that such a computer can pass signals through each other without interference, allowing for much higher component density.
• Quantum Computers.. In late 1993, Seth Lloyd described a general design for a quantum computer which could, in principle, actually be built. The computer consists of a cellular automaton-like array composed of quantum dots, nuclear spins, localized electronic states in a polymer, or any other multistate quantum system which interacts with its neighbors. The units are switched from one state to another by pulses of coherent light, and read in an analogous manner. Lloyd has shown that such a computer could perform both as a parallel digital computer, and as a quantum computer in which (for example) bits can be placed in a superposition of 0 and 1 states. Technical difficulties in building such a computer include finding systems with long-lived localized quantum states, and delivering accurate pulses of light. Recent developments have been bringing quantum computers ever closer to reality; see Science Magazine articles on Quantum Computing.