[Q] Can someone explain to me how storage works? What is topic

I decided to upgrade to Lollipop after holding out for awhile.... before I did though, as I knew I was going to run an RUU so I wouldn't have any problems with the OTA, I copied everything in my "storage" (all folders) to my windows laptop desktop via USB.

After upgrading, I copied it all back, making sure not to over-write anything.

What is strange is when I copied all my folders to my laptop initially, I didn't see a Download folder... which I expected to see. But after looking through the folders I had copied, I saw a folder called storage, and in that folder another called emulated, and then another called "0". In that folder I finally saw my Download folder.

I didn't think much of this at the time, however, when I look at storage from Root Explorer, I note there is a new Download folder at the "root" level of storage, but the storage/emulated/0 path is still there as well.... and following it takes me to my old Download folder....

So...to get back my original folders and contents before I upgraded to Lollipop, I have to copy over every folder in this path up 3 levels. i.e., from /storage/emulated/0/storage/emulated to /storage/emulated.

What is going on? Why is there an "0" and a "legacy" if I go up one level from /storage/emulated/??? Why did my old Download folder end up where it did?

[Q] Can you please explain what is the ROM? topic

Hey, I have really basic information about computers and OSs so I really need some explanations for the case of android smartphone (qualcomm mainly). So let me tell you first what I know (I hope that this is true): For a computer they use EEPROM and it's a type of ROM which is erasable. The bios is stored there and it's the first thing loaded when starting the computer. (It's is easily updatable as I have already updated my bios). For the case of android smartphones I think that they use NVRAM, but I don't know what is NVRAM physically? is it a build-in memory separated from storage devices like on computers?! or is just a partition of internal storage? (internal storage I mean /dev/block/mmcblk0). I found that NVRAM can only be erased using JTAG on some websites but I found that device cloning is done copying mmcblk0 from one phone to another, so that means that NVRAM is located in mmcblk0. And if NVRAM is just a part of mmcblk0 so why is it a read only memory? we can easily write to other partitions, so why not NVRAM?! I'm really confused...

Please share your knowledge, I really need years of studying electronics and computer science to know all this by myself... Thank you all!!