Page "Backplane" Paragraph 10

When a backplane is used with a plug-in single board computer ( SBC ) or system host board ( SHB ), the combination provides the same functionality as a motherboard, providing processing power, memory, I / O and slots for plug-in cards.

While there are a few motherboards that offer more than 8 slots, that is the traditional limit.

In addition, as technology progresses, the availability and number of a particular slot type may be limited in terms of what is currently offered by motherboard manufacturers.