A read-only memory (ROM) image is a file consisting of the data from a ROM chip. It usually contains the data from firmware, an arcade board, or a video game. Used in embedded systems, ROM images can also be used for testing prior to permanent writing to a ROM chip. Actual ROM chip hardware has been replaced in the majority of cases by hard drives, flash memory chips, tapes, and optical drive-based media, such as compact disc read only memory (CD-ROM) and digital versatile disc read only memory (DVD-ROM). The term ROM image is most commonly used to describe any software image — optical or chip-based — that is used during the process of hardware emulation.
In hardware emulation, the term ROM image is incorrectly used to describe any kind of software image. Often, the images used for emulation are not exact copies of the original cartridge, disc, board, or tape image as they are optimized for use with emulators. Emulators use software to replicate the hardware operations of older computer systems, video game consoles, and arcade boards, and the associated image needs to be adapted or collated from several different ROM chip data packages to work correctly in the emulation software. This process of transferring ROM chip data to a ROM image is referred to as dumping.
A benefit that is gained from dumping this data to a ROM image is the ongoing preservation of aging and historically important computer and video game systems and the associated software. As the original media and hardware ages, the risk of permanent loss of the data continues to increase. Copyright holders are often against the dumping of ROM images due to the ability to distribute the image freely and easily over the Internet or on digital media.
The generally understood rule is that it is acceptable to posses ROM images for software if you have previously purchased and own an original copy of the data. The distribution of ROM images sees no further proceeds pass to the intellectual property (IP) holder, but people often prefer to use a ROM image rather than use an original disc or cartridge and risk permanently damaging the data. By utilizing the ROM image as a backup only, many users think that they are not in breach of copyright law, but the legality of this practice remains undefined fully.