General questions about memories, configuration and FPGA systems.

What Socrates wrote is correct. I only add some extra info.

Regarding the subject of storing different configurations/Nios-software into flash, you may read Altera application notes AN458 and AN521, or simply search the website for anything related to Remote Update.

In case you need to select one of the configurations stored in flash, the way of operation is actually this:

FPGA always starts with a base configuration (usually referred to as 'factory'), which is stored at address 0 of configuration device (i.e. epcs or CFI)

This is usually a non-fully operational firmware which only purpose is to boot the real application, user selected by means of dip switches, buttons, serial port command or any method you choose.

The base configuration sets up the remote update core for a fpga reconfiguration using an image at the desired flash address.

Only after this step the actual configuration becomes operational.