See my Initrd and Linux Bootdisk
Lets get a few hard to remember facts straight
This explains perfectly all the ramdisk, ramfs, tmpfs, initrd, and initramfs stuff http://www.linuxfordevices.com/c/a/Linux-For-Devices-Articles/Introducing-initramfs-a-new-model-for-initial-RAM-disks/
ramdisk is a filesystem stored in memory and treated as a block device, it was the first ram file system, but the problem \ is that it's treated as block device, it takes up a set amount of space even if the file system is only half full, and if you want to \ expand it, you have to re-format it just like a block device, and it must have a type, like ext2...
ramfs is the new type of ramdisk created by Torvalds, it is not seen as a block device, and only takes op the size of its data, it can expand \ and strink as data is added or removed. Later the kernel developers created a better ramfs called tmpfs.
initrd (Initial ramdisk) The kernels first root file system, Initrd refers to the type of filesystem being ramdisk. If the initial root file system \ is a ramdisk, the kernel will call /initrc as its first process.
initramfs (Initial ramfs) The kernels first root file system, initramfs refers to a type of filesystem being ramfs (the new method). This \ ramfs is more expandable (not constrained like a Initrd block device). The kernel will call /init (not initrc) if its first file \ system is a ramfs. This is the most common, it is always a CPIO archive. Even though most distro's call it /boot/initrd.img.. it is \ NOT an Initrd (ramdisk), its a CPIO ramfs archive. And actually, since tmpfs is like ramfs (but better), initramfs is actually \ an instance of tmpfs
You can tell if your Initial Disk is a CPIO ramfs, try
$ cp initrd.img-2.6.31-16-generic initrd.img-2.6.31-16-generic.gz $ gunzip initrd.img-2.6.31-16-generic.gz $ file initrd.img-2.6.31-16-generic
of course http://www.logicsupply.com