[Python-Dev] Dictionary sparseness

[Tim Peters]

[Alex Martelli]
> ...
> As CPUs and floating-point units became fast enough, more and more of
> the speed issues with so-called "CPU intensive" bottlenecks in
> mechanical-engineering CAD actually became related to memory-access
> patterns (a phenomenon I had already observed when I worked on IBM
> multi-CPU mainframes with vector-units, being sold as "supercomputers"
> but in fact still having complex and deep memory hierarchies -- Cray guys
> of the time such as Tim no doubt had it easier!-).

Indeed, Seymour Cray used to say a supercomputer is a machine that
transforms a CPU-bound program into an I/0-bound program, and didn't want
anything "in between" complicating that view.  As a result, optimizing
programs to run on Crays was, while still arbitrarily difficult, generally a
monotonic process, rarely beset by "mysterious regressions" along the way.

Now that gigabyte+ RAM boxes are becoming common, I wonder when someone will
figure out that the VM machinery is just slowing them down <0.9 wink>.