3.  Progress in miniaturization and computing
power in recent decades has been impressive.
But there are physical limits to the ways
electrons can be shunted around tiny circuits
in a wafer of silicon.
 For this reason, researchers have been looking
into alternative technologies that might
someday deliver performance unthinkable
with traditional semiconductors.
4.  Some of the most interesting approaches deal
with the very small—the world of molecules
and the even more minuscule subatomic realm
where the strange laws of quantum mechanics
come into play.
Molecules:
 Among molecules with a high profile in
computer- technology research, the two most
intriguing are the carbon nanotube
and DNA(deoxyribonucleic acid), the basic
vehicle of heredity in the biological world.
5.
6.
7.  Engineers have already developed carbon nanotube
transistors that can carry as much as 1,000 times the
current accommodated by the copper wires used in
silicon chips.
 Today’s computer processors, however, may have a
billion transistors or more. Still to be solved are the
problems of how to make similarly enormous numbers
of high-quality nanotubes and how to arrange them in
circuits—while keeping costs down.
 Nanotubes’ potential is enormous.
8.  Their use in computer storage and memory devices
raises the prospect of ultra-high capacity hard drives
as well as fast random-access memory (RAM) that,
unlike today’s RAM chips, would not lose its contents
when the power is turned off.
 Such storage devices could make possible instant-
booting computers, handheld computers with upwards
of 10 gigabytes of memory, and MP3 players that hold
exponentially more songs than today’s devices.
9.
10.
11.  Meanwhile, in 2003 a pair of U.S. scientists
developed the first interactive DNA computing
system, an enzyme-driven device called MAYA
that played unbeatable tic-tac toe.
 Its human opponent made moves by putting
DNA into little wells making up the game board;
each well contained enzymes that acted as “logic
gates” controlling the device’s response to the
input data.
12.
13.  Today’s encryption systems for protecting information
transmitted via such channels as the Internet tend to rely on
mathematical problems that would take an enormous —
hopefully unfeasible —amount of time and effort to solve.
 For example, one of the most popular encryption methods,
called RSA (from the initials of its inventors), depends on
the fact that it is very hard to find the prime factors of a
very large number—that is, the prime numbers that
produce the number when multiplied by each other.
 This approach works for now, but what if mathematicians
make a breakthrough? As it happens, one of the most
celebrated unsolved problems in mathematics, the so-called
Riemann hypothesis, deals with the pattern that might lurk
behind the seeming randomness of prime numbers.
14.  The keys required for encrypting and
decrypting messages are represented in this
instance by a pattern
of particles of light, or photons, with
certain characteristics.
 Interception by an eavesdropper will leave
obvious traces, revealing that the key has
been detected.