some question about ramdisk

[lmc83]

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