An engineer must perform a nondisruptive software upgrade on a dual supervisor Cisco Nexus 7000 series switch. What is the cause of the upgrade being disruptive?

While `show install all impact` is a critical command to check for potential disruptions before an upgrade, not issuing it doesn't cause the disruption itself; rather, it means a potential disruption might not be identified in advance.

The command `install all kickstart image system image` is the standard procedure for performing a unified image upgrade on Nexus 7000, and by itself, it is designed to be nondisruptive if other conditions for ISSU (In-Service Software Upgrade) are met.

There is no general limitation that attempting to simultaneously upgrade more than three cards causes disruption; the upgrade process is designed to handle modules in a coordinated fashion during ISSU.

Modifying configuration settings or altering network connections (e.g., adding/removing cables, changing port states) during a software upgrade on a Cisco Nexus 7000 series switch can interfere with the upgrade process, prevent a graceful supervisor switchover, and ultimately lead to a disruptive upgrade or even system instability. Best practice dictates no changes during an upgrade.