In a note to his staff last Friday, Michael Harte, the Commonwealth Bank's chief information officer, said he wanted to let them all know of the reasons he'd decided to leave the CBA.Harte's, however, concentrated on setting out the progress made towards modernisation since he joined the bank in 2006, the new products and services developed and the change in culture towards one where staff had a deeper empathy with their customers. An odd note was struck in Harte's comments on the decrease in severity one incidents over the past eight years: "There were about 400 high impact system issues per year when I started. Today we have seen an 84 per cent reduction in these types of incidents and the trend line continues to go down."He then noted that incidents will still occur and must be dealt with humbly and quickly. "The systems, processes, hardware and technology we have invested in overtime mean we are able to run key applications with an uptime of more than 99.999 per cent."On these numbers, the implied annual rate of "sev1" incidents at CBA remains at around 70, the same level as 2008, rather than the 7 incidents per year referred to by the bank's chef executive Ian Narev in his 2012 results presentation. And neither of CBA's sev1 performance metrics for its new SAP-based core banking system - whether 7 or 70 -are exceptional. Westpac, still in the process of moving to CSC's Celeriti core banking system, said in its 2012-13 results announcement that its severity 1 numbers were down from 30 per month to "less than 4 per month" - that is, less than 47 per annum. Westpac's numbers aside, industry sources indicate that, globally, among the Tier 1 banks running CSC's Hogan-based core banking systems, each bank has experienced less than a single sev 1 incident each year. Clearly some more work needs to be done, especially if the bank is to continue to achieve the 99.999 per cent uptime target he referred to. However, in doing so, Harte, was merely expressing a view he's shared several times - and as recently as last week - that none of CBA's core systems should experience more than "five minutes of downtime" in any given year.Although the note to staff last week didn't include it among his achievements, Harte's "five minutes downtime" sound bite may become his longest lasting legacy to the Australian banking sector. Otherwise known as the 99.999 per cent or "5x9s availability", it's the same standard being set by the RBA for the New Payments Platform and it is also what eftpos will be applying for their new systems. "Meeting this standard is virtually an industry requirement - none of the banks can afford not to," said one senior banking technology executive.