Notes for the Lifebox, the Seashell, and the Soul - Rudy Rucker

Notes for The Lifebox, the Seashell, and the Soul, by Rudy Rucker
depending on how much RAM the particular machine has. The “random access” aspect of
the memory has to do with the fact that each memory cell has an address, and the processor is
able to read or write the contents of a cell at any desired address without having to traverse
all of the intermediate cells. If necessary, a computer can actually use more memory than it
has in its RAM by reading and writing to extra disk, which function as a slower kind of
RAM. (To read something off a disk, you need to physically move a read head to a certain
address position. Reading from a given location on a RAM chip is more like pulsing a signal
into an address wire and getting an answer back right away.)
***
How does the processor know how to carry out instructions? This is handled by a
tiny program, known as microcode, that is coded right into the processor. Microcode
interprets strings of bits as instructions to do things with the registers. The microcode lets the
processor behave as if a certain sequence of bits means, say, “add the contents of register BX
to the contents of register AX.” The physical logic of the etched-in circuitry has tiny adding
machines, multipliers, logic gates, and the like.
Confession of Anxiety in Chapter One
Right now, writing this, I feel uneasy. I want The Lifebox, the Seashell, and the Soul
to be a fun book, and here I am talking about arithmetic. And now, as if that’s not boring
enough, I’ve got to start in on tax forms? Jesus wept.
Rap about Halting Being Bad
Your experience with pencil-and-paper computations, such as multiplying numbers,
may have left you with the impression that a computation has to terminate with an answer.
But this need not be true. A computation can be ongoing, with no specific termination time
contemplated — think of a flowing river or of a computer screen-saver. Each of the
successive states is an output linked to a moment in time.
Speaking of time, how long does a computation continue? We won’t impose any
bound at all. Certain kinds of computation will indeed signal when they’ve arrived at a
desired result ⎯ for instance by beeping or by printing a result ⎯ and then halt in the sense
of no longer changing their states. But there’s a sense in which such computational processes
continue after their halting point. It’s just that after they halt they remain in a constant state.
For a computer that’s supposed to calculate a number halting, is usually viewed as a
good thing, but for a living being ⎯ which is also a kind of computation ⎯ halting has the
bad connotation of death. Most naturally occurring computational processes are things that
we like to keep going as long as possible.
Feasibility is Relative
Feasibility is relative concept. To say a computation is feasible, you not only need to
specify both the hardware and software of the computer system M that you plan to use as
well as the amount of time T that you would be willing to wait for an answer. It would be
more precise to speak of M-T-feasibility than simply of feasibility. Just to be precise, let’s
say that if I speak of feasibility, I’m normally thinking of M as being as good an electronic
computer as currently exists on Earth, loaded with the best software algorithms we currently
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