When faced with "computer says no" moments in shops and banks, Jan Stuart is occasionally tempted to leap over the counter and bash the till in frustration. Just like the rest of us. But unlike the rest of us, some thumps from Stuart's fingers could do some good. Why? Because, as a Cobol programmer, she may be able to fix the problem.

The "common business-oriented language" that has provided 59-year-old Stuart with a career through to retirement age marks its 50th birthday this year. The day to celebrate is slippery - Cobol didn't just scroll on to a terminal one day and ask the user to hit "Compile" - but 1959 is the year that the language came into being.

And Cobol is still in business. According to David Stephenson, the UK manager for the software provider Micro Focus, "some 70% to 80% of UK plc business transactions are still based on Cobol".

Stephenson's company is an important player in the provision of tools to manage existing Cobol systems, not to mention building new applications, so an optimistic stance is to be expected. But are companies really relying on a half-century-old invention to handle large chunks of their dealings? Mike Madden, development service manager with the catalogue-shopping firm JD Williams, believes so.

Better known for its online stores, such as Simply Be and Fifty Plus, Madden says JD Williams remains highly dependent on Cobol applications. "We have a huge commitment to Cobol," he says. "About 50% of our mainframe systems use it."

Why? "Simple - we haven't found anything faster than Cobol for batch-processing," Madden says. "We use other languages, such as Java, for customer-facing websites, but Cobol is for order processing. The code matches business logic, unlike other languages."

Matching underwear

So, knicker-buying Simply Be customers are greeted by a pretty-in-pink Java interface, but when the order reaches the backroom, charcoal-grey Cobol code takes over the processing grunt work.

Stuart is familiar with this set-up. Many of her organisation's data-processing systems remain reliant on Cobol, she says. "When Windows arrived, our executives all wanted their computers to look that way," says Stuart, "so front ends changed. But behind the scenes, the Cobol systems remain."

Stuart asked for her company not to be named, though it is a well-known financial institution. We also contacted the major UK banks, but none would talk publicly about what technology drives their backrooms, with most citing security concerns.

However, while Cobol is evidently still at large in business, a term used repeatedly to describe such systems is "legacy".

"Legacy code supports our business model," says Madden. "We have around 2,500 programs running in Cobol and 60 of the 100 staff in our department are focused on legacy systems."

Mike Gilpin, from the market research company Forrester, says that the company's most recent related survey found that 32% of enterprises say they still use Cobol for development or maintenance. But it's worth pointing out that in the same survey, in which multiple answers were permitted and no breakdown of "development" and "maintenance" was specified, Microsoft Visual Basic, .Net and Java top the languages-used charts, at 65% apiece.

A lot of this maintenance and development takes place on IBM products. The company's software group director of product delivery and strategy, Charles Chu, says that he doesn't think "legacy" is pejorative. "Business constantly evolves," he adds, "but there are 250bn lines of Cobol code working well worldwide. Why would companies replace systems that are working well?"

The impression is that Cobol is to business what the internal-combustion engine is to motoring: it's been around for so long, and is installed in so many places, with so much supporting infrastructure, that doing something different - even if the end result could be better - would be impossibly costly.

Obviously, Cobol hasn't stood still for 50 years. Older Cobol systems have been updated to integrate with today's modish object-oriented programming languages. Barely a year ago, for instance, IBM updated its Enterprise Cobol to version 4.1, and further revisions are on the way.

Is there a new generation of programmers ready to grab the Cobol cudgels? Michael Coughlan, a lecturer at the University of Limerick, thinks so. The institution's computer science student intake tailed off 10 years ago. The course evolved and Coughlan says that around half his fourth-year students now take the elective modules where Cobol is used.

Bugs mean business

Of course, a decade ago, folks got worked up about something called the millennium bug. The debate over how serious was the threat that seemed to detonate with a "phut" has been played out, but Cobol code was high on the offender list, resulting in a mini-boom for Cobol developers. Then it all went quiet, the web entered the ascendant and Cobol got forgotten again. Well, by the outside world at least.

Stuart holds that Cobol cobblers remain in demand, and she estimates that those prepared to travel can expect to earn up to £80,000 a year. Moreover, despite imminent retirement, Stuart isn't about to issue the End-Perform command on her work just yet: "I'll continue doing bits and pieces. Cobol is just a great language for business and it isn't going away."

And business, it appears, agrees.

Begin: drinking 99 bottles

According to Michael Coughlan, a lecturer at the University of Limerick, one of Cobol's perceived drawbacks is its verbosity. But he reckons that's also one of its strengths. "It's not just a write-only language," he says. "You can come back years later and understand the code."

This opinion is shared by Mike Gilpin, of Forrester, who is an ex-Cobol programmer. "Cobol is one of the few languages written in the last 50 years that's readable and understandable," he says. And he's scathing about the readability of more fashionable languages, such as PHP and Java: "Modern programming languages are ridiculously hard to understand."

True? Well, judge for yourself at the 99 Bottles Of Beer project website. What began in 1994 as a geek joke to save bandwidth by turning the song lyrics into six lines of code in the Basic language has grown to versions of the program in 1,259 (and counting) different programming languages. Don't miss the Lolcode version!