Questions about ROM in android/PC?

You're pretty confused after you googled full form of "ROM" and came up with Just "Read Only Memory". Yes, its right but its in the text-book term when the computer world was evolving. First of all, ROM what you read isn't same in Android. 1) ROM in-terms of Android refers to the Operating System files. Installing a custom ROM in Android short of means you flashed (formatted) your device. Here, "Radio" contains the your all kinds of drivers are not replaced unless you specifically flash some zip to replace the driver. & The another term is "Firmware" which is also sort of similar to Radio but goes into lower hardware interaction level than that. It is sort of baseband allocated to your device, by your OEM depending upon the Region you're in. ~For example, if you want to change the OS, you just flash another custom ROM. ~If your WiFi drivers or GPS or something other is not working, you flash the specific ZIP file, which modifies your driver. ~ But, if you want to change your Firmwar (or baseband) you'll have to flash your Android Device with Odin which appropriate firmware file from samsfirmware.com 2) Another concept here regarding your point no. 2 is root in Linux: There are 4 types of users in Linux: a) Normal User (eg: home path: /home/UserName) b) Group User (eg: Group of people having separate account, but group name is same. In such case Group User's home path goes like /GroupName/UserName.) c) Other User (eg: Remote Access user) d) Root (eg: sort of like Administrator in Windows, but this user has all the access, Including modifying the File System, changing the Start Up mount's fstab. In short, almost ANYTHING.) Now, except root user in above here, no one has access to modify the file system. So basically for them file system is like Read-Only. How is this related to Android? -> Android uses Linux as its core OS. When you install several applications, each "Application" falls under the normal user in Android. Means, no application can access another application's data unless that another application provided such a facility through Content Providers. But, through root access, you can read/mount system/modify the file system same as I described in Linux. So, thats almost all about Read-Only System and Root in Android. Your half last 2nd question doesn't make sense to me. 3) ROM has the files to run your mobile system. It has the framework specific files, SystemUI files, user and system binary files etc. But, It doesn't change the firmware or drivers as I said earlier. 4) No. "Latest" CyanogenMod can't even run on AVD (android Emulator)! All what you see, was tested on real devices. These custom ROMs are modified from the original source-code released by Google on git. I hope, you'll find yourself pretty clear now. :)