Gilbert Strang is a quiet man with a rare talent: helping others understand linear algebra. He's written a half-dozen popular college textbooks, and for years a few hundred students at the elite Massachusetts Institute of Technology have been privileged to take his course.

Recently, with the growth of computer science, demand to understand linear algebra has surged. But so has the number of students Strang can teach.

An MIT initiative called "OpenCourseWare" makes virtually all the school's courses available online for free — lecture notes, readings, tests and often video lectures. Strang's Math 18.06 course is among the most popular, with visitors downloading his lectures more than 1.3 million times since June alone.

Strang's classroom is the world.

In his Istanbul dormitory, Kemal Burcak Kaplan, an undergraduate at Bogazici University, downloads Strang's lectures to try to boost his grade in a class there. Outside Calcutta, graduate student Sriram Chandrasekaran uses them to brush up on matrices for his engineering courses at the elite Indian Institute of Technology.

Many "students" are college teachers themselves, like Sheraz ali Khan at a small engineering institute in Peshawar, Pakistan, and Noorali Jiwaji, at the Open University of Tanzania. They use Strang and other MIT professors as guides in designing their own classes, and direct students to MIT's courses for help.

Others are closer to MIT's Cambridge, Mass., campus. Some are MIT students and alumni, while others have no connection at all — like Gus Whelan, a retiree on nearby Cape Cod, and Dustin Darcy, a 27-year-old video game programmer in Los Angeles who uses linear algebra regularly in his work.

"Rather than going through my old, dusty books," Darcy said, "I thought I might as well go through it from the top and see if I learn something new."

There has never been a more exciting time for the intellectually curious.

The world's top universities have come late to the world of online education, but they're arriving at last, creating an all-you-can eat online buffet of information.

And mostly, they are giving it away.

MIT's initiative is the largest, but the trend is spreading. More than 100 universities worldwide, including Johns Hopkins, Tufts and Notre Dame, have joined MIT in a consortium of schools promoting their own open courseware. You no longer need a Princeton ID to hear the prominent guests who speak regularly on campus, just an Internet connection. This month, Yale announced it would make material from seven popular courses available online, with 30 more to follow.

As with many technology trends, new services and platforms are driving change. Last spring marked the debut of "iTunes U," a section of Apple's popular music and video downloading service now publicly hosting free material from 28 colleges. Meanwhile, the University of California, Berkeley recently announced it would be the first to make full course lectures available on YouTube. Berkeley was already posting lectures, but YouTube has dramatically expanded their reach.

If there isn't yet something for everyone, it's only a matter of time. On iTunes, popular recent downloads include a climate change panel at Stanford, lectures on existentialism by Cal-Berkeley professor Hubert Dreyfus, and a performance of Mozart's requiem by the Duke Chapel Choir. Berkeley's offerings include 48 classes, from "Engineering Thermodynamics" to "Human Emotion."

"It's almost as good as being there," said Whelan, the Massachusetts retiree, of the MIT classes he has sampled. "The only thing that's lacking is the pressure." He says he usually doesn't do the homework assignments, but adds: "Now that I'm not in school, I don't have to do that anymore."

YouTube, iTunes, OpenCourseWare — none are the full college experience. You can't raise your hand and ask a question. You can't get a letter of recommendation.

And most importantly, almost everywhere, you can't get credit or earn a degree.

That caveat, however, is what has made all this possible.

When the Internet emerged, experts predicted it would revolutionize higher education, cutting its tether to a college campus. Technology could help solve one of the fundamental challenges of the 21st century: providing a mass population with higher education at a time when a college degree was increasingly essential for economic success.

Today, the Internet has indeed transformed higher education. A multibillion-dollar industry, both for-profit and nonprofit, has sprung up offering online training and degrees. Figures from the Sloan Consortium, an online learning group, report about 3.5 million students are signed up for at least one online course — or about 20 percent of all students at degree-granting institutions.

But it hasn't been as clear what role — if any — elite universities would play in what experts call the "massification" of higher education. Their finances are based on prestige, which means turning students away, not enrolling more. How could they teach the masses without diminishing the value of their degree?

But MIT's 2001 debut of OpenCourseWare epitomized a key insight: Elite universities can separate their credential from their teaching — and give at least parts of their teaching away as a public service. They aren't diminishing their reputations at all. In fact, they are expanding their reach and reputation.

It turns out there is extraordinary demand for bits and pieces of the education places like MIT provide, even without the diploma.

OpenCourseWare's site gets more than 1 million hits per month, with translated versions getting 500,000 more. About 60 percent of users are outside the United States. About 15 percent are educators, and 30 percent students at other universities. About half have no university affiliation.

"I think the fundamental realization is that distance learning will solve the problem of access to certification, but there's a larger problem, which is access to information," says Steve Carson, director of external relations for the MIT initiative.

"If you're going to work as a public health professional, you need the certification," Carson says. "If you're working in a community" — say, in Africa — "you don't need the certification. You just need access to the information."

About 7,200 miles from Cambridge, the Polytechnic of Namibia in is the kind of place eager to learn from MIT. Though barely a decade old, the school in the young African nation's capital Windhoek, is poised to play a key role in the country's development. It's one of 84 sites in Africa where MIT has shipped its course materials on hard drives for institutions to store locally on their own networks. With bandwidth costing about 1,000 times its price in the United States, patching into OpenCourseWare over the Internet would crash the school's fragile networks.

CIO Laurent Evrard says Polytechnic takes pride in standards on par with top global peers — he notes how U.S. exchange students get credit for work there — and says students like using OpenCourseWear to see how they stack up.

"Everybody here knows about MIT," he says, though it doesn't hurt that the school rector — its top official — is an alumnus.

On the opposite coast of southern Africa, Jiwaji says most of his Tanzanian students have never heard of MIT. Students use the courses "because it gives them a tool. They feel lost and they don't have good books," Jiwaji says. "They need a guide to help them."

His distance university — with 30,000 registered students — has OpenCourseWare available at centers around the capital of Dar es Salaam. There, it gets an impressive 600 hits per day, mostly in management classes.

Though it's found a wider audience, OpenCourseWare was originally intended for teachers. The idea wasn't just to show off MIT's geniuses but to share its innovative teaching methods. After examining an MIT course called "Machine Structures," Khan, the Pakistani professor, redesigned his lab assignments for a computer science class to get students more involved, asking them to design and build their own microprocessors.

"It really encourages the students to discover and try something new," he said. "Normally the stress here is on how things work, not on creating things of your own."

MIT's free offerings focus mostly on well-organized texts like syllabuses and readings, along with an expanding video lecture collection. Others, like Stanford and Bowdoin College in Maine, provide more polish, editing and features.

Berkeley, meanwhile, is focused less on bells and whistles than on ramping up its ability to roll out content with a system that automatically records and posts lectures. Berkeley's eight YouTube courses drew 1.5 million downloads in the first month, said Ben Hubbard, co-manager of the webcast.berkeley program, and the school is being inundated with requests to post more.

"That's why we're so focused on automation," he said. "Our motto is 'Fiat Lux' — 'let there be light.' We feel like this is a great way to let the light of Berkeley shine out on the world."

A big obstacle is cost. Professors are reluctant to participate unless staff are provided to help with logistics. A major expense is video camera operators, unless schools can persuade lecturers to stand still at the lectern. MIT estimates OpenCourseWear costs a hefty $20,000 per course. Money from the William and Flora Hewlett Foundation started the project, but from now on it will rely mostly on contributions from MIT's budget and endowment, and from visitor donations.

But there are direct benefits. Small schools like Bowdoin can use iTunes to show prospective students the richness of their offerings. MIT reports half its incoming students have already checked out OpenCourseWare.

Meanwhile, half of MIT alumni use OpenCourseWare, too. And alumni who stay connected with the intellectual life at their alma maters are more likely to donate.

MIT and other schools also emphasize the services benefit their paying customers — the students. On-campus use at MIT and Berkeley spikes during exams, as students review lectures. Fears that technology would hurt class attendance have proved unfounded, at least at MIT, where 96 six percent of instructors reported no decline.

Will the free offerings of elite universities ever reduce demand for the full — and full-price — experience at places like MIT? Carson doubts it. Networking, late-night arguments over pizza, back-and-forth with professors — that's where the real value lies, and even MIT's technology may never catch up with that.

For teachers like Strang, his expanded reach is no more than a minor inconvenience — occasional e-mailed questions from "students." And it's a major reward.

"My life is in teaching," he says. "To have a chance do that with a world audience is just wonderful."