Does Ubuntu run from a CD/DVD save data ONLY in memory?

If I create a proper LiveCD and run the OS from the disc does it save any information on a hard-drive or is it ALL saved to the PC's memory? I've looked around for a clear, direct "yes/no" answer to this question but I can't seem find it anywhere. Common sense would say yes but you never know and what I need to do requires an OS that does not use Flash(usb) or Magnetic(hd) storage of any kind while in operation.

From the answers to this question, we can safely believe that no data is stored on the hard disk unless we choose to save it to hard disk(persistence).

As for a definitve answer check out this post on stackoverflow which explains that it is a ramdisk.

Quoting from the Stackoverflow answer to the above said question:

Believe it or not, it's a ramdisk :) All live distros mount a temporary hard disk in RAM memory. The process is completely user-transparent and is all because of the magic of Linux kernel.

The OS, in fact, first allocates an area of your RAM memory into a virtual device, then mounts it as a regular hard drive in your file system.

Once you reboot, you lose all your data from that ramdrive.

For more detailed information regarding this, check out the Wikipedia article on Live Cd explaining the technique of its working.