Text 12. Software Reliability

An important facet of software quality is software reliability. With the advent of the computer age, computers, as well as the software running on them, are playing a vital role in our daily lives. We may not have noticed, but appliances such as washing machines, telephones, TVs and watches, are having their analog and mechanical parts replaced by CPUs and software. The computer industry is booming.

Software does not age, rust, wear-out, deform or crack. Furthermore, software has no shape, color, material, mass. It can not be seen or touched, but it has a physical existence and is crucial to system functionality.

Optimists would think that once the software can run correctly, it will be correct forever. A series of tragedies and chaos caused by software proves this to be wrong. Software can make decisions, but can be just as unreliable as human beings. The British destroyer Sheffield was sunk because the radar system identified an incoming missile as “friendly”.

Soft ware errors cost the U.S. economy $60 billion annually in rework (переделка), lost productivity and actual damages (реальные убытки): Hartford Coliseum Collapse (1978, Connecticut, USA) cost $70 million plus another $20 million damage to the local economy. Just hours after thousands of fans had left the Hartford Coliseum, the steel-latticed roof (стальная решетчатая крыша) collapsed under the weight of wet snow. What was the cause? The programmer of the CAD (САПР) software used to design the Coliseum, incorrectly assumed the steel roof supports (опора) would only face pure compression. But when one of the supports unexpectedly buckled (подкосилась) from the snow, it set off a chain reaction that brought down (сбила) the other roof sections like dominoes.

In 1999 the U.K. Passport Agency implemented a new Siemens com-

puter system, which failed to issue passports on time for a half million British citizens. The Agency had to pay millions in compensation, staff overtime and umbrellas for people queuing in the rain for passports. It cost the Agency £12, 600 million and caused mass inconvenience. The cause was that the passport Agency rolled out its new computer system without adequately testing it or training its staff. At the same time, a law change required all children under 16 travelling abroad to obtain a passport, resulting in a huge spike (всплеск) in passport demand that overwhelmed (захлестнул) the buggy (глючная) new computer system.

Software can also have small unnoticeable errors or drifts that can culminate into a disaster. On February 25, 1991, during the Gulf war, a software rounding system (ошибка округления) incorrectly calculated the time, causing the Patriot system to ignore the incoming Scud missile. The missile destroyed an American Army barracks. 28 soldiers died, 100 were injured.

There are more scary stories to tell. This makes us wondering whether software is reliable at all. You can hardly ruin your clothes if the embedded software in your washing machine issues erroneous commands; but in airplanes, radiation therapy machines, a software error can easily claim people’s lives. The reliability of software is simply a matter of life and death.