When Tech Upgrades Go Awry

Planes grounded.Office work ground to a halt.The past few days have served as a vivid reminder of our deep and mostly unthinking dependence on technology.

It’s powerful, it’s ubiquitous and yet, at times, it can be alarmingly fragile.Old technology and new technology were the culprits.Starting on Thursday, Microsoft’s email, office and meeting software — delivered over the internet — stopped working for millions of users worldwide.

Those cloud services were restored on Saturday.On Friday, the Federal Aviation Administration ordered all flights grounded after some of its aged data-handling equipment faltered, raising potential safety issues.The order was lifted Friday night, but hundreds of thousands of passengers were stranded over the weekend.A telling irony is that both meltdowns were caused by attempted “upgrades” that went awry.

New cables in the case of the F.A.A., and a planned increase in computing capacity in Microsoft’s case.The upgrade challenge underlines the extraordinary complexity of multilayered combinations of hardware and software in major computing systems.Upset the delicate balance by making changes, even in an effort to improve performance, and you risk a system crash.That happens frequently, though widespread outages are uncommon.

The last big one came two years ago, when what should have been a routine software update by a security company, CrowdStrike, crashed millions of computers around the world that were running Microsoft Windows.Airlines grounded flights.

Subways stopped.Operators of 911 lines couldn’t dispatch help.

Stores shut down.Hospitals canceled surgeries.

It took days to restore all the impaired machines.We are having trouble retrieving the article content.Please enable JavaScript in your browser settings.Thank you for your patience while we verify access.If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.Thank you for your patience while we verify...