The move comes as part of a three-year A$1.8 billion (US$1.3 billion) dollar overhaul of the bank's operations, which aims to reduce complexity and standardize systems across multiple franchised business units in Australia and the UK.

Head of technology for NAB's projects division, Paul Burgin told Computerworld lengthy duration between upgrades for the bank was necessitated by a critical need for stability across the branch network, with the NAB unwilling to take chances with customer services until upgrade stability was well and truly proven in the field.

"We run a very large branch network and we have to put a value proposition against stability and our ability to provide certainty in customer service. In that sense, going to an established operating system rather than the brand new thing actually has appeal.

"That said, in the lab we have been testing remote upgrades to Vista (the next iteration of Windows) and we know that when we are ready and comfortable Vista is stable - and it suits us to make the move - we can actually do the upgrade as a remote refresh," Burgin said.

The project is also estimated to require an upgrade of about 20,000 PCs for the bank, with a request for proposal understood to be ready for release to the market as soon as the NAB completes a requirements audit of its existing hardware.