A Commonplace Book

Today I want to think about CPUs. A little bit of silicon moving bytes around. Pretend you are a beginning programmer. Tear away all that knowledge you've built up about programming, software, management, and get back to the lowest level Von Neumann fundamental stuff. Wipe J2EE out of your mind for a moment. Think Bytes.
Why are we doing this? I think that some of the biggest mistakes people make even at the highest architectural levels come from having a weak or broken understanding of a few simple things at the very lowest levels. You've built a marvelous palace but the foundation is a mess. Instead of a nice cement slab, you've got rubble down there. So the palace looks nice but occasionally the bathtub slides across the bathroom floor and you have no idea what's going on.

[A] clever hacker will read my code and notice that I'm only allocating 1000 bytes and hoping it will be enough, and they'll find some clever way to trick me into strcatting a 1100 byte string into my 1000 bytes of memory, thus overwriting the stack frame and changing the return address so that when this function returns, it executes some code which the hacker himself wrote. This is what they're talking about when they say that a particular program has a buffer overflow susceptibility. It was the number one cause of hacks and worms in the olden days before Microsoft Outlook made hacking easy enough for teenagers to do.

Shlemiel the painter's algorithm
Shlemiel gets a job as a street painter, painting the dotted lines down the middle of the road. On the first day he takes a can of paint out to the road and finishes 300 yards of the road. "That's pretty good!" says his boss, "you're a fast worker!" and pays him a kopeck.
The next day Shlemiel only gets 150 yards done. "Well, that's not nearly as good as yesterday, but you're still a fast worker. 150 yards is respectable," and pays him a kopeck.
The next day Shlemiel paints 30 yards of the road. "Only 30!" shouts his boss. "That's unacceptable! On the first day you did ten times that much work! What's going on?"
"I can't help it," says Shlemiel. "Every day I get farther and farther away from the paint can!"