some question about ramdisk

hi,
I have some question about initrd.
If I have a compressed ramdisk image: initrd.gz put at a memory location for example: 0x00070000 (in fact, in my application, it is flash)

1. what is the meaning of initrd_start in rd.c (linux-2.4.0)? Is it means 0x00070000?
or is it means the initrd.gz will be decompressed to the location initrd_start?

2. I'm tracing the rd.c and found that initrd_load() will be called only if initrd_start != 0, but for my testing case, it seems always initrd_start==0.
Which kernel parameter can modify the initrd_start?

3. How to tell the kernel that I have a initrd who's image is located 0x00070000?
I saw the Document/kernel-parameters.txt, is seems doesn't have suitable parameter for me to use.

Should I modify the kernel source code to fit my requirement? I've saw the "How-To: make root/boot disk", it use floppy's specific sector as ramdisk image,
I think is's a little similar to my application,
I will try to just specify memory location instead of reading from floppy's specific sector.

Thanks in advance for you help

Liang Ming-Chung