What component allows a technician to install more add-on cards than available expansion slots?

A riser card is designed specifically to expand the number of available expansion slots in a computer system or server. It achieves this by providing a way to mount additional add-on cards at an angle, which allows them to fit into a limited physical space, typically parallel to the motherboard. This flexibility is crucial in environments where maximizing available slots is necessary, such as in high-density servers or workstations.

In contrast, while backplanes can connect multiple components or cards, they do not inherently increase the number of expansion slots. A CPU daughterboard is used to add processors or additional processing capacity, but it doesn't provide more slots for add-on cards. An array controller is focused on managing RAID storage and does not pertain to the installation of expansion cards.

Thus, the riser card is the most effective component for allowing a technician to install more add-on cards than the available expansion slots, enhancing the system's overall versatility and capability.