boot linux from an ide

[Gin]

I use FILO as the payload to boot from a Hard Disk, which has a
installed linux on it. I noticed if I enabled the ide stream. It tries
to read the ELF header from my IDE drive. But I thought the FILO payload
should be the one to load the image from the IDE drive. When does it
come in and play the role?
Anyone can explain the flow of booting if I try to load the INSTALLED
linux from a IDE drive.

Gin