Best explanation with illustrations that I've come across....

Over the years I have come to describe Test Driven Development in terms of three simple rules. They are:

1. You are not allowed to write any production code unless it is to make a failing unit test pass.
2. You are not allowed to write any more of a unit test than is sufficient to fail; and compilation failures are failures.
3. You are not allowed to write any more production code than is sufficient to pass the one failing unit test.

You must begin by writing a unit test for the functionality that you intend to write. But by rule 2, you can't write very much of that unit test. As soon as the unit test code fails to compile, or fails an assertion, you must stop and write production code. But by rule 3 you can only write the production code that makes the test compile or pass, and no more.

Ellison says he has already stopped the carnage at Sun, less than four months after the sale closed in January. "Their management made some very bad decisions that damaged their business and allowed us to buy them for a bargain price," he told Reuters. He added that he expects profit from Sun's operations to boost Oracle's earnings in the current quarter, which ends May 31.

The integration has proceeded swiftly, says Ellison, because a protracted antitrust review in Europe gave Oracle time to draw up an exhaustive plan for resuscitating Sun. In typical Ellison fashion, he took a hands-on approach to the integration, choosing to meet directly with technical managers at Sun as often as four days a week to diagnose its problems, rather than delegating the work to underlings.

There are no super programming languages, only super programmers. And they tend to be super jerks. I should know – I used to be one. What would really make a programming language be super powered is the ability to be used by normal people.

Please click through to read the entire post... It's worth the read.

“There are a whole other group of folks who play this game,” Mr. Tabb said. “They put low limit orders into the market for this exact purpose — for when the markets go into free fall.”
...

Unfortunately for those investors, the exchanges have rules in place to cancel or rescind any trades that are associated with erroneous or unusual trading activity.

“If there is an order that gets printed and it is so far away from the market that it was clearly wrong, the exchanges have the right to break it and, in fact, they do it fairly often,” Mr. Tabb said. “It just doesn’t happen with this magnitude.”

On Friday, the Nasdaq market said it would cancel all trades that had occurred in the 20-minute period between 2:40 p.m. and 3 p.m. on Thursday that were 60 percent higher or lower than the last trade at 2:40. “This decision,” the exchange noted on its Web site, “cannot be appealed.”

About 4,000 trades were broken on Thursday after being identified as clearly erroneous as per exchange rules, Mr. Niederauer said, and the wild fluctuations were certain to prompt more scrutiny of high-frequency trading from regulators.

"We as an industry have to say how much is too much of this technology," Mr. Niederauer said.

"This was a massive liquidation panic," said Bill Strazzullo, chief market strategist for Bell Curve Trading, a Freehold, N.J., technical-research firm.

As the losses accelerated, there were little to no "buy" orders left in many stocks and other assets, causing a plunge that saw some securities spiral to near zero. "You just blew through everything," he said.

A number of high-frequency firms closing down in the midst of a sharp market drop can "widen markets out substantially," said Jamie Selway, managing director of New York broker White Cap Trading.

High-frequency firms have in recent years become central to how the market operates, growing to account for about two-thirds of daily market volume, according to industry estimates.

The firms use high-powered computers to send "buy" and "sell" orders to the market at rapid speeds. High-frequency traders have said part of the value they add to markets is the liquidity they bring—being at the ready to swiftly complete a trade. Some of these firms have said that, were it not for them, the 2008 market declines would have been worse.

When I started my second company, in 1988, also in Silicon Valley -- the industry was approaching a level of maturity that, in tech, warns of a looming implosion. I was too young and inexperienced to know this, but the signs were everywhere. A few years before if you had a good idea, you could ship a product, promote it, build a user base, and find liquidity. Now the dominant companies had grown so big they were starting to choke the ecosystem. And the entrepreneurs who were showing up were less the bright-eyed engineers with big ideas, and more of the carpetbagging MBAs with pyramid schemes. Gotta say the VCs typically went for the MBAs. The era of the engineer, if it wasn't over, was certainly waning.