There's so much risk and expense associated with replacing a legacy system that it usually takes serious problems to force the issue, but the longer CIOs wait to make that decision, the more difficult it will be for their organizations to make the transition smoothly.

Love them or loathe them, legacy systems just seem to hang around like - depending on how much grief they are giving you - either that arthritic yet much loved and ever faithful old dog or an extremely unpleasant and persistent smell.

"Today, many organizations rely heavily on critical back-end applications that reside on legacy systems," says Jim Rhyne, distinguished engineer and lead architect, eServer Tools Technology and Enterprise Transformation at IBM. "Even after 35 years legacy systems are still the technology foundation of the majority of the world's largest companies. In fact, legacy systems have been called the modern-day equivalent of buried treasure: Hidden in back rooms and locked behind proprietary code is a wealth of information that could be used to support e-business strategies."

However, while some legacy systems seem to have been blessed with the secret of immortality, even the most conservative IT organization eventually reaches the point where it can no longer deny that select ancient systems are on their last legs and must be redesigned and replaced. And since software systems do not wear out, and since many legacy systems can appear to be operating like sterling workhorses while actually running like dogs, that realization can sometimes hit well after the point where the transition might be made easily and relatively risk-free.

"For decades, various IT gurus have predicted the demise of the mainframe and the need to rewrite - or 'replatform' - core applications," notes Ken Orr, fellow, Cutter Business Technology Council.

"Years later, many, if not most, of these applications continue to perform their required function 24x7x365. This lulled many organizations into the position that it was simply impossible to rewrite many mission-critical applications and that the best one could do was make minor changes around the edges of these applications. Moreover, many of those who know the most about these applications are approaching retirement, so they are reluctant to take on the task of rewriting code and prefer simply to continue applying life support," Orr says.

In the world of the ageing workforce, many highly knowledgeable employees use their knowledge as the ultimate form of job security, which is no small thing in this world of uncertainty, Orr says. Against a backdrop of casual work and mounting job insecurity, who can blame them for wanting to leverage the maxim about knowledge being power? After all, take away their legacy systems and plenty of organizations would flounder.

Yet even the most backward IT organization recognizes that some systems eventually must be redesigned and replaced, Orr says. It is just that it cannot be done overnight, the transition can cost a small fortune, and it can be extremely difficult to recognize the risks upfront.

The fact is, legacy systems are brittle, inflexible and impenetrable, and they are still around in their multitudes. And they spell R-I-S-K - presenting risks to the organizations that keep them, particularly by way of strategic business risks associated with their expense and inflexibility, but also risks to those attempting to modernize them. Their modernization is a problematic and uncertain process that many organizations will undertake at some stage during their lifetime.

The dilemma is compounded by the phenomenal cost of replacing a legacy system, or migrating off such a system, which can run into millions of dollars. Unsurprisingly, many companies try to change their legacy systems incrementally to spread the cost. Knowing they must provide customers and employees with access to data stored in legacy systems via the Internet, but recognizing legacy systems are not "Internet compatible", leaves many IT organizations facing the question of extending their legacy system or scrapping it in favour of a whole new system.