help: about *.flash

hi,

i am sorry for my poor english.

in my system, nios program is stored in ext_flash, and hardware image is strored in epcs. the "cfi_flash.elf" need to be converted to "cfi_flash.flash". i knew "boot_loader_cfi.srec" was needed, and inserted it in front of the "cfi_flash.elf" using elf2flash, then "cfi_flash.flash" was generated.

i found the cfi_flash.flash was not "cfi_flash.elf" adding "boot_loader_cfi.scre" simply. i want to know the Algorithm in process. or i want to know why there need s-record format file, can some other formant be used? for example?

thanks!