What you get often depends on what you've already got. In technology this is known as the legacy problem, and most people see it in their desktop computers. Yet although an old PC may boot up slowly and crash easily, its problems can usually be solved with a reboot, and no lives are at stake.

But what if the legacy technology dates back not 25 years but 75 years or even a century? What if it were vitally important to millions of people? And what if it were so outmoded that newly minted engineers could barely recognize it

That's the state of things below the streets of New York City, where time has stood still. Hardly anyone took notice until 25 January, when a fire knocked out a subway line serving large swaths of Manhattan, Brooklyn, and Queens. The fire gutted a signal room containing some 600 electromechanical relays and a rat's nest of signal wires, crucial components of a fixed-block signaling system that has kept proper headway between trains since the subway system was inaugurated. The signal method dates back to when Manhattan had barns as well as skyscrapers.

Photo: Jeff Christensen/Reuters

Subterranean Snafu: New York City's subway system slowed in January when a fire in a signal room fried relays and wires of eye-popping antiguity.

Many of the roasted relays and wires turn out to have been not technological descendants of the originals but the originals themselves, put in place for the line's first run, on 10 September 1932 [see Behind 19th-Century Technology]. That makes it one of the system's newer lines; others go back to 1904.

There were reasons to retain the relic devices. They worked, though not well; upgrades would have been lost on commuters; a new design could not be implemented without disrupting the system; and the monopoly in charge of it all had grown set in its ways.

You can find such petrified technology in subways around the world, including those in Paris, dating back to 1900; Boston (1897); Budapest, Hungary (1896); and the oldest of them all, London, whose Underground went into service on 10 January 1863. Subways tend to preserve such relics in part because the cramped working environments underground make it hard to build new systems without interfering with service.

Surprisingly, two companies, Alstom Signaling Inc., in West Henrietta, N.Y., and Union Switch and Signal, in Pittsburgh, still supply the subway with the relays. Perhaps they, too, have rooms that time forgot, where men in spats turn out paleoparts under the warm glow of a carbon-filament bulb. In any event, the companies would not open the cellar door or discuss any part of their businesses.

Equally secretive was MTA New York City Transit, which gave few details on the relay system's innards. Some doubt as to the transit authority's mastery of such details was raised immediately after the fire, when its president, Lawrence G. Reuter, startled the city and the world by saying it would take five years to restore full service.

Within a week, however, workarounds enabled nearly normal service. A spokesman for New York City Transit did a little spinning by telling IEEE Spectrum that the transit authority president had meant it would take five years to complete the design, procurement, funding, and construction of the signal room's permanent replacement.

To be fair, the transit authority has begun modernizing its subterranean traffic signals, albeit slowly. This summer, after a six-year US $288 million investment, the L line [see 21st-Century Technology], which traverses 20 of the system's 1200 kilometers and serves 24 of its 468 stations, will finally begin computerized train operations. The train will not require a conductor or train operator to maintain speed, open and close doors, or control its route.

Preliminary design work has also begun on replacing the signals and their relays on the No. 7 line, which runs across midtown Manhattan and passes Shea Stadium on its way to its terminal in Flushing, Queens.

"The two biggest obstacles to changing out the signals are funding and finding a way to install the new technology in a subway system that runs 24 hours a day, seven days a week," says Charlie Seaton, a spokesman for the transit authority.

For years the city has been loath to raise fares to pay for upgrades in the subway. By the early 1980s, when federal and state funds allowed the transit authority to make improvements, its first priority was to clean things up. Stations were refurbished, and rickety and graffiti-covered trains were replaced by air-conditioned models. Meanwhile, in the tunnels and signal rooms, it was still 1932.

Even a few billion dollars extra wouldn't solve the problem, because the subway's always-on service requirement limits the rate of work. When a company decides to replace mainframes with networked servers, it sets the new system up in parallel and shuts down the old system only after a safe period. Since subway control systems are right on the tracks, they cannot be replaced without disrupting service.

"And you wouldn't believe the pressure we were under from local politicians and advocacy groups when we shut down the L line on weekends" for the modernization, said Seaton.

To repair any part of the subway requires shutdowns, which must be done mainly at night and on weekends. To upgrade the entire system would take 35 years, the transit authority estimates. Of course, by then, it will again be out of date.

How much would a system-wide signals upgrade cost? Seaton wouldn't venture even a guess.

But any New Yorker could tell you: "Fuhgeddaboutit."