The principle behind the curve--that 80 percent of the consequences come from 20 percent of the causes--is rooted in a 19th-century observation about the distribution of wealth. But it also illustrates the challenge for the builders of, the world's largest-selling software packages.
As they scramble to get the programs to users by the end of the year, the equation is a simple one: making software reliable for most personal computer users is relatively easy; it is another matter, in a PC universe with tens of thousands of peripherals and software applications, to defeat the remaining bugs that cause significant problems for some users.
The effort to overhaul the Windows operating system, originally code-named Longhorn and since renamed Vista, was meant to offer a transformation to a new software foundation. But several ambitious initiatives failed to materialize in time, and the project started over from scratch three years ago. The result is more an evolutionary shift, focusing on visual modernization and ease of use.
Still, the company is within a month of completing work on new versions of both Windows and Office, having apparently overcome technical hurdles that as recently as August seemed to signal a quagmire.
"It looked bleak; it was a slog, but in the end this was a technical problem, and there was a turning point," said Bharat Shyam, 37, a computer scientist who is director of Windows program management. "We've confounded the analysts and the press."
As October arrived, a vote of confidence came from Wall Street when a Goldman Sachs analyst, Richard G. Sherlund,. "The Vista development organization has made rapid progress delivering improvements to Vista's performance, reliability, and compatibility," he said.
(On Friday, the company released what it said would be, named Release Candidate 2. If the response from testers is positive, the software will go into production by the end of the month.)
The debugging process has been urgent, with Microsoft scheduled to introduce Windows Vista and Office 2007 to corporate customers by the end of the year, and to home users early next year.
This coordinated introduction is a multibillion-dollar proposition for Microsoft, which has Windows running on some 845 million computers worldwide and Office on more than 450 million, according to the market research firm Gartner.
Indeed, it was the vast scale of the Windows testing program that saved the software development projects. Over the summer, the company began an extraordinary bug-tracking effort, abetted by volunteers and corporate partners who ran free copies of both Windows and Office designed to send data detailing each crash back to Microsoft computers.
The Office package, for example, has been tested by more than 3.5 million users; last month alone, more than 700,000 PCs were running the software, generating more than 46 million separate work sessions. At Microsoft, 53,000 employee computers are running test versions.
Vista has also been tested extensively. More than half a million computer users have installed Vista test software, and 450,000 of the systems have sent crash data back to Microsoft.
Such data supplements the company's own testing in a center for Office referred to as the Big Button Room, for the array of switches, lights and other apparatus that fill the space. (A similar Vista room has a less interesting name--Windows Test Technologies.)
This is where special software automatically exercises programs rapidly while looking for errors.
The testing effort for Windows Vista has been led by Mario Garzia, Microsoft's director of Windows reliability. A former Bell Labs software engineer, Garzia says the complexity of the Vista and Office effort dwarfs anything he undertook for the nation's telephone network.
"Everything is easy if you do it for a limited number of things," he said. "When I was at Bell Labs, the problems were complex, but nothing compared to this."