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Why Desktop Multiprocessing Has Speed Limits
Computerworld (10/05/09) Vol. 43, No. 30, P. 24; Wood, Lamont

Despite the mainstreaming of multicore processors for desktops, not
every desktop application can be rewritten for multicore frameworks,
which means some bottlenecks will persist.  "If you have a task that
cannot be parallelized and you are currently on a plateau of
performance in a single-processor environment, you will not see that
task getting significantly faster in the future," says analyst Tom
Halfhill.  Adobe Systems' Russell Williams points out that performance
does not scale linearly even with parallelization on account of memory
bandwidth issues and delays dictated by interprocessor communications.
Analyst Jim Turley says that, overall, consumer operating systems
"don't do anything smart" with multicore architecture.  "We have to
reinvent computing, and get away from the fundamental premises we
inherited from von Neumann," says Microsoft technical fellow Burton
Smith.  "He assumed one instruction would be executed at a time, and
we are no longer even maintaining the appearance of one instruction at
a time." Analyst Rob Enderle notes that most applications will operate
on only a single core, which means that the benefits of a multicore
architecture only come when multiple applications are run.  "What we'd
all like is a magic compiler that takes yesterday's source code and
spreads it across multiple cores, and that is just not happening,"
says Turley.  Despite the performance issues, vendors prefer multicore
processors because they can facilitate a higher level of power
efficiency.  "Using multiple cores will let us get more performance
while staying within the power envelope," says Acer's Glenn Jystad.

http://www.computerworld.com/s/article/342870/The_Desktop_Traffic_Jam?intsrc=print_latest