My Samsung Galaxy SIII seems to have an internal SD card as internal memory, and no ROM (Read-Only Memory).
As far as I know, ROM refers to a type of memory which can be only modified by attaching a cable from it to a special device and flashing; once the ROM is flashed, it is for all purposes read-only from the point of view of the users logging into the OS. Many sites report that one of the benefits of rooting is installing custom ROMs.
So why is installing an alternative system UI such as CyanogenMod still referred to as installing a custom ROM? Isn't it just replacing some files in the /system directory with some other files, i.e., deleting or backing up some old files and copying the replacement files to that directory?


  • Yeah, perhaps older and coarser devices still have ROMs, but I doubt any of the newer Android phones still have ROMs. Thanks. Dec 14, 2014 at 20:38
  • 2
    You've tagged your question with the rom tag. Have you checked the corresponding tag-wiki? Find an explanation there. // Hint: Many of our tag-wikis hold good descriptions and first-aid, so it's always worth checking them :)
    – Izzy
    Dec 14, 2014 at 21:24
  • Thanks. I've checked the ROM tag wiki (sorry, was not aware of this SE feature). It provided me with useful information. Dec 15, 2014 at 13:10

1 Answer 1


Old things tend to stick around. In everyday things (toasters, microwaves etc) there is some kind of software to control the device. That software is installed by the manufacturer and is usually hard to change, in practice read-only. While you can flash the system partition on android, with some electronic devices you needed to and still need to plug in some specific pins to some manufacturer application on a pc.

Nowadays ROM refers to the software by the manufacturer that drives the device, such as the /boot and /system partitions.

  • I would just add that it is viewed from the users perspective. Looking from their perspective, you can only write to the internal user storage, and the system indeed is ROM because the user can only read it and cant write it. The only real ROMs are the ones that after writing burn the writing fuse and by that disable any possible write channels.
    – Chapz
    Dec 4, 2015 at 11:24

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