Protecting legacy applications with virtual operating systems

A surprising number of humdrum, boring applications end up in the third category over time. Sadly, the mission-criticality of such an application might only be manifested the day it stops working. A mission critical application is like fuel or coffee. You only realize how much you depend on it when it is taken away from you.

Given that the mission-criticality of applications in the third category grows stealthily over time, it follows that by the time anybody notices how mission critical an application has become, technology may have moved on. Your newly recognized mission critical system is now also known as the 'legacy' system. Oh dear. Operating systems have moved on. Development frameworks/languages have moved on. GUIs have moved on. The staff who know how the darned application works and can pick it up when it falls over have moved on. Oh dear.

The PC revolution is now old enough for the term 'legacy application' to refer to something that was crafted in the late Seventies/Early Eighties. However, given the rate of change in this industry, even applications created, say, 9 years ago are seriously legacy at this stage. Remember Windows 95? Sounds very dated doesn't it? That was only 9 years ago although in Windows applications terms it was eons ago.

How to keep legacy applications ticking over without hindering your ability to move onward with newer technology? Many, many years ago, the mainframe people at IBM[1] cooked up an interesting way to do this. Simply put, they virtualized the concept of an operating system. (i.e. a single machine in which multiple 'sessions' could each be running a different operating system). They even named the operating system after the idea - virtual machines - VM[2].

This idea has, in recent years, started to make serious inroads in the world of PC operating systems. Three examples I have come across at customer sites recently are VMware[3], VirtualPC[4] and Crossover[5].

Using VMWare or Virtual PC, for example, you could have Windows XP as your main operating system hosting fully operational, fully self-contained Windows 2000 and Windows 95 operating systems. With Crossover you could work in Linux with a Windows 95 operating system running away in a little window of the screen. It's quite an amusing thing to see in operation. Amusing and massively practical.

Virtualization of operating systems is a growing trend. A trend you can leverage to extend the life of your mission critical applications. If the health of legacy applications is keeping you awake at night I suggest taking a long hard look at virtualization.