ROM means only memory to read, that means memory filled with non-solvent information with memory, unlike RAM, first of all, you should know that a custom ROM can be said differently, The most common "custom rom" users have still been Frenchized to this word, it is possible to find this concept under the name "Custom Rome", "Alternative Rome", "Alternative System" or "Custom System".
On the operating system of Android, there are usually two types of ROMs: the manufacturer (official) and the hackers who make for the community (they can compile from the sources) The establishment of the official ROM is quite simple because it is usually Enough to follow the instructions provided by the manufacturers of the device.
There are three types of official Rom:
Official Rom which is installed automatically after the restart of the terminal
Official ROMs that are installed manually in Download Mode (previously downloaded)
Official roms that install manually in recovery mode (using .zip file)
Regarding informal roms, the user must put his hand in Greece.
A custom ROM does not only make cosmetic changes.
Note: To install, custom ROM does not require root. At the moment you have installed an alternate recovery, then you can install any custom ROM with your device. However, it is very common to include options for a custom ROM that super-user (root) privileges need to be fully exploited. Without it, you can still enjoy it, but you make a cross on these famous additional properties which require the development of the rights of the administrator (super user).
Why install Custom Roms?
Generally, when a user is going to an alternate system, it's a new version of Android to enjoy. reason ? Once the manufacturer has left the software monitoring of one of its products, then the only solution is a custom ROM that can extend your Android life for several months, and for many years! Of course, we should not forget that the community supports the terminal in question. Without it, installing a custom ROM on a product supported by the community is almost impossible, unless you know how to cook yourself, of course!
In the most popular and most consistent ROM customs, we can refer to Lineage Os which takes the torch after the disappearance of the cyanogenomod, but there are many others such as Paranoid android or Omni Rom, many other less known but still interesting features: Slim Roms, Dirty Unicorns provide a comprehensive compatibility with Pac ROM ... Depending on your terminal, you can get your hands on the ROM tutorial Sm be that the ultimate source for most French, or platform Aksda developers customs of Rom.