Massively parallel computers (MPCs), characterized by their scalable architectures, are a viable platform on which to solve the so-called grand-challenge problems. These distributed-memory systems are expandable and can achieve a proportional performance increase without changing the basic architecture. In order to take full advantage of scalable hardware, the application software must also be scalable to exploit the increased computing capacity.

Even those who understand something like this may find themselves wishing they didn't. Shewchuk offers a second example for the benefit of those who know the subject so well that any information "grandmothered" in an introduction will be known to the audience instinctively. So you see two opposite evils to watch out for in telling your audience what it knows already.

On the other hand, there are cases when your audience will be made comfortable by what they've heard before:

• they've forgotten all or part of the information
• a slightly different perspective may jog their memories or present a new idea
• they might not be sure they're in the right place :-)
• like Hobbits, they find comfort in the familiar

Even if any or all of these are true, you have to make sure that when you're grandmothering your audience, you're comprehensible and you don't take too long at it. :-)

References

Shewchuk, J. "Three Sins of Authors in Computer Science and Math." http://www.cs.cmu.edu/~jrs/sins.html
Tolkien, J. R. R. The Hobbit and the Lord of the Rings. Boston: Houghton-Mifflin, 1998. ISBN 0-61800-225-1