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I regularly get criticism from detractors who object
to my arguments in favor of
adopting a non-algorithmic, signal-based, synchronous software model. The following
is a compiled list of objections followed by my rebuttals. I will add
new items to the list as they come to my attention.
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| 1. Hardware is more reliable than software because
correcting flaws in hardware is very difficult and expensive, so
they get it right the first time. |
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| Correcting flaws in mission-critical software is
equally expensive. Just ask any manufacturer who has had to recall
thousands of products due to a defect in the software. Ask NASA or
the FAA how expensive and dangerous malfunctioning software can
be. Mission and safety critical software goes through the same
stringent testing as hardware. The fact remains that algorithmic software
is still more prone to failure than hardware regardless of how
careful the designers and testers are. |
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| 2. Hardware has just as many bugs as software.
Just look at the errata sheets for a new chip. |
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| Nobody is claiming that there are no bugs in
hardware. The claim is that almost all bugs in hardware are found,
corrected and documented during the testing process. Once released, an
integrated circuit will almost never fail except for physical
reasons. By contrast, there are almost always hidden bugs in
released software that the quality control process invariably fails to
catch during testing. In addition, most hardware bugs are due to
physical defects introduced during manufacturing or the result
of bad physical layout. |
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| 3. Hardware is more reliable than software because
it is less complex. |
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| Not true for two reasons. First, if
one compares hardware and software of roughly equal complexity,
the hardware is invariably orders of magnitude more stable than
the software. Second, when most people talk about hardware, they
usually think of a single IC chip or function. They overlook the
fact that a chip is more comparable to one or more subroutines or
objects in a software application. A hardware system, such as a
computer, usually consists of
multiple chips working together in very complex ways. Combining
any number of chips to form large systems is not known to increase
their logical failure rate after release. Likewise, combining many functions on a single chip does not degrade the quality of
the finished product. By contrast, combining subroutines to create
larger programs is known to increase the likelihood of failure
in deployed software systems. |
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| 4. The brain is
asynchronous, not synchronous as you claim. |
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| This is not supported by
research in neurobiology. One of the most amazing aspects of the
brain that has come to light in the last half century is the
existence of synchronizing oscillations mostly in the 10 to 120
Hertz range. |
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| 5. Contrary to your claims, the
human brain is a very unreliable system. It continually makes
mistakes, creates memories of events that never happened and
often makes irrational decisions.
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| Unlike our current computer
systems, the brain is self-correcting, that is to say, it uses a
trial and error process to modify itself. Making and correcting
mistakes is what it is programmed to do. To expect a child to
ride a bicycle without falling or running into obstacles is like
faulting a chess program for not playing tic-tac-toe. Barring a
physical failure, the brain always does what it is programmed to
do, flawlessly, even if it turns out to be a mistake.
In
order to survive in an uncertain and chaotic environment, the
brain uses a technique known as pattern completion to fill in
missing or unknown information. This mechanism makes it possible
for us to understand a garbled conversation in a noisy room or
recognize a partially occluded face. It also makes it possible
for animals to recognize danger in the wild even when the
predator is hidden from view. Certainly, the mechanism often
leads to false assumptions but this must not be equated with
failure on the part of the brain. This is the way it is supposed
to work. Anything else would lead to extinction. As an aside,
our
future intelligent robots will behave in a very similar manner.
The super rational, logical and unerring Mr. Spock is a modern
myth.
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| 6. What about the famous
Pentium FDIV bug? Isn't that a case of hardware failing after
release? |
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| No. The Pentium floating point
processor did exactly what it was supposed to do, which was
to fetch a value from a location in a table in on-chip memory.
It just so happened that the table was wrong. This Pentium
division bug is a perfect example of blaming hardware for a
fault in the embedded software. For whatever reason, the quality
control department had failed to test a portion of the design.
The promise of the synchronous model is not to eliminate design
mistakes, although it can go a long way toward that goal (see
this news item). The promise
is this: once a design is tested to behave a certain way, it
will continue to behave in the same way barring a physical
failure. One cannot fault a chess program for not playing
tic-tac-toe. |
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Send all comments to Louis
Savain
©2006 Louis Savain
Copy and distribute freely
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