The effect is called giant magnetoresistance, but it enables amazing things at the miniature level. Two European scientists won the 2007 Nobel Prize in physics yesterday for their discoveries of the phenomenon, which spurred some of computing’s most astonishing developments, from video-playing handheld devices to PCs whose storage capacity now seems all but limitless.

France’s Albert Fert and Germany’s Peter Grünberg independently described giant magnetoresistance in 1988, then saw the electronics industry apply it in disks with large amounts of storage.

“I can hardly think of an application that has a bigger bang than the magnetic hard drive industry,” Phil Schewe, a physicist and spokesman for the American Institute of Physics, said. “Every one of us probably owns three or four or five devices, probably more, that depend on billions of bits of information stored on something the size of a dime.”

Mr. Fert, 69, is scientific director of the Mixed Unit for Physics at CNRS/Thales in Orsay, France, while Mr. Grünberg, 68, is a professor at the Institute of Solid State Research in Jülich, Germany. They will share the $1.5 million prize. Mr. Grünberg told reporters he was not too surprised to win the Nobel. “Because I have received a lot of awards, I was often asked, ‘When will the big award come?'” Mr. Grünberg said.

Asked if he’d thought his discovery would have such wide application, Mr. Fert told the Associated Press: “You can never predict in physics. … These days, when I go to my grocer and see him type on a computer, I say, ‘Wow, he’s using something I put together in my mind.’ It’s wonderful.”

Here’s how it works: As a metal disk spins inside a hard drive, an arm with a sensitive electromagnetic head at its tip hovers over the disk, somewhat like the needle on a record player (though it doesn’t make contact). This head reads bits of data by registering the magnetic bearing of individual particles; it writes data by changing that magnetic orientation.

For disk drives to increase in capacity, those magnetic particles must become smaller, so more can be packed into the same amount of space. But these ever-tinier materials produce fainter magnetic signals, which means the read-write head in the disk drive has to become more sensitive.

What Messrs. Fert and Grünberg independently discovered was that extremely thin layers of alternating metals could detect remarkably weak changes in magnetism — and translate them into “giant” changes in electrical resistance.

In other words, the particles used in data storage could get much denser and still produce the electrical signals that computers read as ones or zeros as they do their business.

It took until 1997 for giant magnetoresistance to get translated from Messrs. Fert and Grünberg’s raw science into a product for the disk market. That was led by IBM Corp., where researcher Stuart Parkin developed a way to incorporate Messrs. Fert and Grünberg’s findings into the cost-effective manufacturing process already used to produce disk drives. One result can be measured in disk-drive density — the number of bits that can be squeezed into a given area. In the ’90s, disk density was improving about 60% a year. But GMR sparked a few years in which density doubled — a 100% rise — and costs still fell.