How is initramfs_data.cpio handled by the kernel during boot?

Hello, I have a question concerning initramfs support. When the kernel is built, a initramfs_data.cpio archive is created in linux-2.6.x/usr. This archive can be compressed by selecting the compression type in .config (gzip, bzip2, lzma or lzo). When the kernel build is finished, what does this initramfs_data.cpio become? Is it put somewhere is vmlinux executable? If so, where? Is it expanded in the INITRAMFS section defined in the vmlinux.lds.S Finally, how is this cpio archive handled by the kernel? Thanks in advance for your help.