use ramdisk as root file system

[zhu shi song]

I now can boot my QDIA6T(vt8601/vt82c686b) MB using
hard disk as root file system though there is no vga
turned on.  But I don't need HD. I hope I can mount
RAMDisk as my root filesystem which can be read and
written.  How should I do to start such work?  I have
read some material about initrd but I don't understand
it very clearly. 
tks
zhu

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