But Union Bank of California NA in San Francisco is the more typical example: Apart from scattered file-and-print and Web servers, it runs only a few application-monitoring tools on Linux. "We haven't launched any true business applications on Linux yet," said Rick Curry, vice president of infrastructure engineering at Union Bank. "Most of us [in the banking industry] are still kicking the tires."

In contrast with brokerages, many of which were quick to embrace the use of Linux and other open-source technologies, U.S. banks have been downright laggards. From branch-office systems to core financial databases, Linux has yet to prove -- to many bank IT executives, anyway -- that in clustered configurations it can scale to match the performance of incumbent mainframes.

Even some Linux vendors concede that the retail banking market has been a disappointment for them thus far.

"There are not hundreds of banks using Linux, but we are seeing a larger chunk starting to ask the question," said Kim Lorusso, financial services marketing manager at Novell Inc., owner of the SUSE Linux operating system.

Staying put