If the hard drive is not recognized as a bootable volume in the BIOS, you have two choices:
/boot on an alternate device. This can be an ordinary hard disk drive, or even a CD-ROM or USB key device. The idea is to get the kernel and initrd loaded off this (possibly slow) device, then finish the boot off the real root filesystem.
- If you're feeling up for a challenge, you could theoretically use coreboot to flash a Linux kernel and initrd image right into your BIOS chips (assuming you have large enough BIOS flash chips for this).
You may also want to consider running your iRAM module in a RAID-1 configuration with a normal hard drive partition. If you did this, you could boot off your hard drive as normal, and use the iRAM as, essentially, a fast, persistent cache device. This has the major advantage that your data will remain on the normal hard drive if the iRAM drive runs out of batteries.