POUGHKEEPSIE, N.Y. (AP) – They could be bigger than refrigerators. Modern laptops can run laps around them and palm-sized iPods have more memory than their central units.

But IBM’s System/360 was a big deal when it was unveiled 40 years ago on April 7, 1964. While the term mainframe had been used before the 360 series, these computers were different. All the machines could run the same software – a novel idea at the time – and they could be used to figure everything from paychecks to payloads.

Technology historians say that made the 360 one of the most influential computer rollouts ever.

“They set the standard that’s been followed for 40 years,” said Nathaniel J. Davis, professor of computer engineering at Virginia Tech.

Computer sales were good for IBM in the early 60s, although businesses upgrading their computer systems also had to buy new software. IBM feared that incompatibility could cause problems down the road.

“They had different tape attachments, different disc attachments. Nothing could be moved from one to another,” said Bob O. Evans, an IBM executive who helped develop the 360. “So the customers who bought those behemoths of the time were stuck there.”

The company’s answer: a hush-hush $5 billion research and development project sometimes described as a Manhattan Project for computers. It was a big gamble at odds with IBM’s starchy, risk-averse image.

In April 1964, the company unveiled a “family” of computer systems dubbed 360 because of its all-around compatibility with other computers in the system.

The concept revolutionized the industry; companies upgrading their systems no longer had to pay for new programs, said Davis.

IBM staged a splashy debut with dozens of news conferences nationwide and overseas. Company chairman Thomas Watson Jr. called it the most important product announcement in the company’s history. IBM chartered a train to bring New York City reporters 70 miles upriver to Poughkeepsie for the debut.

For the time, it was an impressive sight. The higher end Model 50 had a central processing unit the size of two refrigerators placed front to back, fronted by a panel of flashing lights, flip switches and time counters that looked like car odometers.

Central units could be simultaneously connected to up to 248 terminals to retrieve and upload data, which was be stored on separate tape readers or disc units.

The central units’ memory capacity topped out at about 8 megabytes (for comparison, iPod minis, at 4 gigabytes, have 500 times more memory). The Model 50 had a processor speed of 2 megahertz, compared with typical personal computers today that measure speed in gigahertz.

“Your laptop is more than this is,” said veteran IBM executive Paul Vomaska, motioning to a Model 50 on display at IBM’s Poughkeepsie plant. “I find that mind boggling.”

The initial reaction to the 360 was … quiet, at least for a couple of months, according to Evans. But once customers digested the idea, orders came in beyond expectations. Allstate, Bank of America and NASA were among the first customers.

“There was a computer industry before the IBM 360 was announced, but it was never the same after that – Honeywell, RCA, National Cash Register, Burroughs, GE – were forced to develop computer families of their own,” according to a historical report released in January by the research firm IDC.

While the designs were conservative, IBM had superior sales and service, said Dag Spicer of the Computer History Museum in Mountain View, Calif. He said IBM gave deep discounts to universities, meaning students who graduated into business world ordered – what else? – IBM.

Forty years later, IBM is still a dominant maker of mainframes. But IBM now competes in a far more complex market featuring other systems that can perform operations once the exclusive purview of mainframes. Some industry officials have declared mainframe computing as extinct as the dinosaur.

IBM responded by nicknaming its newest mainframe system, the z990, “T-Rex.” Revenues for the z-series grew 33 percent in the fourth quarter of 2003, said IDC analyst Steve Josselyn.

After a dip in the mainframe market lasting into the early 90s, they have caught on with larger users who see it as more secure, simpler and less expensive than distributed systems, Davis said.

AP-ES-04-06-04 1330EDT