When you install a software update, replace or remove all, not just some, of the older subsystems in each product that you install. When a server or workstation contains software subsystems from different releases of a product, compatibility problems result that can be very difficult to diagnose. Use showprods with the -n argument to detect subsystems that are not from the same product release.
When Inst makes its initial installation selections, it automatically selects any updates to subsystems that are already installed. In addition, it selects subsystems that are new with this release and designated as default ("Required and Default Subsystems"). Subsystems that you omitted from the previous installation, even subsystems with a default designation (d in list output) are not selected for installation. In many cases, you can examine the selections with list and give the go command without making any selection changes.
If you see a message about changed configuration files after the installation is complete, follow the directions in "Merging Configuration Files" to merge configuration files. If you do not merge changed configuration files, a message about changed configuration files is posted during the next several system reboots.