How long should a piece of software last – a couple of months, a few years or several decades?

It is a complicated question, and likely to be met with another query: how long is a piece of string?

Different applications are written for different functions – some tools are written with short-term aims in mind, others with lasting objectives to integrate systems and departments. But long-term or short-term, IT professionals are well aware that any application is capable of overstaying its welcome.

The financial services industry, for example, is famed for its use of legacy systems, the replacement of which can be an excruciating process.

IT managers forced to replace such systems regularly roll out the phrase: ‘It was only meant to last a few months, but ended up being used for quite a few years.’

Gannod and Cheng – writing in an academic journal in 1993 – suggest software maintenance has long been a problem facing software professionals, where the average age of software is between 10 and 15 years.

Their analysis provides a sense of the challenges the IT department faces when managing a host of legacy applications. But it was produced 13 years ago, and since that time the technology manager has also had to deal with the rise of the internet, the phenomenal growth of outsourcing and the implementation of mobile services.

More and companies are also now beginning to treat software as a service, buying applications to suit specific business requirements.

Analyst Gartner predicts that by 2010 more than 80 per cent of new applications will be composed of assembled service components, and suggests that the useful life of applications will continue to shrink to the ‘seemingly absurd limits’ of just-in time and disposable applications.

It seems, then, that the age of the 15-year old piece of software, chugging away in the back office, is about to pass – it if has not already.

Computing recently reported on how the UK Patent Office is consulting UK businesses on their innovation plans, to make patents easier to obtain (20 July).

The new guidance will have particular relevance to the IT industry, as inventors and small firms provide the tools for the throwaway era.

So, we ask again: how long do you think a piece of software should last? If you answer: ‘longer than a piece of string’, you may be in danger of being left behind.