I have read about the differences between the two from stackoverflow. But I am still finding it difficult to understand tmpfs and the real advantages of initramfs over initrd.
I find that on RedHat EL 5 or Ubuntu 12.04, I have only initrd files in /boot. However RedHat EL 6 has both intird and intramfs files. Does that mean only Redhat 6 has implemented intiramfs and we still have initrd image there?
If you by Redhat mean the distribution, which was discontinued a decade ago, then it might be true, that it only supported initrd and not initramfs. But on newer distributions, the initrd names in /boot are just named like that for historical reasons.
There was a period where distributions supported both. The kernel knew the difference and could tell the difference at boot time. But for simplicity of the tools generating the boot configuration, the same file name was used for both formats.
The actual initrd has been deprecated for a long time. You had to create a file system, which needed to have a fixed size, and you'd need that much memory for it. With initramfs the memory usage would adjust to the size of the actual files there, and it is easier to generate, when you don't need to figure out the size of the file system before putting files into it.
