A ROM image, or simply ROM, is a computer file which contains a copy of the data from a read-only memory chip, often from a video game cartridge, a computer's firmware, or from an arcade game's main board. The term is frequently used in the context of emulation, whereby older games or computer firmware are copied to ROM files on modern computers and can, using a piece of software known as an emulator, be run on the newer computer.
ROM images are also used when developing for embedded computers. Software which is being developed for embedded computers is often written to ROM files for testing on a standard computer before it is written to a ROM chip for use in the embedded system. At present, this article deals mainly with the use of ROM in relation to emulation.
ROM chips, while still in use, have been replaced in many instances by optical media such as CD-ROMs and DVD-ROMs, magnetic media such as hard disks and magnetic tapes and, more recently, Flash Memory chips. However, the term ROM is commonly also used to cover many of these newer media so, for instance, a computer game copied from a magnetic tape may also be incorrectly referred to as a ROM. The correct names for tape and disk 'roms' are tape image and disk image, respectively. Images copied from optical media are also called ISO images, after one of the standard file systems for optical media, ISO 9660. Many ROMs used by emulators, and particularly console emulators, are not true images of the ROM chips in the cartridge. They are often modified to allow easier functionality in emulators through methods such as combining the images from multiple ROM chips.
Dumping ROMs and creating imagesEdit
ROMs can be copied from the read-only memory chips found in cartridge-based games and many arcade machines using a dedicated device in a process known as dumping. For most common home video game systems, these devices are widely available. Dumping ROMs from arcade machines, which in fact are highly customized PCBs, often requires individual setups for each machine along with a large amount of expertise.
Creating images from other media is often considerably easier and can often be performed with off-the-shelf hardware. For example, the creation of tape images from games stored on magnetic tapes (from, for example, the Sinclair ZX80 computer) generally involves simply playing the magnetic tape using a standard audio tape player connected to the line-in of a PC sound card. This is then recorded to an audio file and transformed into a tape image file using another program. Likewise, many CD and DVD games may be copied using a standard PC CD/DVD drive.
The lifespan of digital media is rarely great. While black-and-white photographs may survive for a century or more, many digital media can become unreadable after only 10 years. This is beginning to become a problem as early computer systems may be presently fifty or sixty years old while early home video consoles may be almost thirty years old. Due to this aging, there is a significant worry that many early computer and video games may not survive without being transferred to new media. So, those with an interest in preservation are actively seeking older arcade and video games and attempting to dump them to ROMs. When stored on standardized media such as CD-ROMs and DVD-ROMs, they can be copied to future media with significantly reduced effort.
The trend towards mass digital distribution of ROMs images, while potentially damaging to copyright holders, may also have a positive effect on preservation. While over time many original copies of older games may deteriorate, be broken or thrown away, a copy in ROM or Image form may be distributed throughout the world, allowing games which would otherwise have been lost a greater chance of survival.
Copy prevention mechanismsEdit
While ROM images are often used as a means of preserving the history of computer games, they are also often used to facilitate the unauthorized copying and redistribution of modern games. Seeing this as potentially reducing sales of their products, many game companies have incorporated features into newer games which are designed to prevent copying, while still allowing the original game to be played. For instance, the Nintendo GameCube used non-standard 8 cm DVD-like optical media which for a long time prevented games from being copied to PCs. It was not until a security hole was found in Phantasy Star Online Episode I & II that GameCube games could be successfully copied to a PC, using the Gamecube itself to read the discs.
The trading of ROMs over the Internet is widespread. Many methods are used for such distribution, including:
- Hypertext Transfer Protocol and File Transfer Protocol
- Direct Connect hubs
- Usenet binaries
Although the large size of games for recent consoles makes the distribution of more than one game at a time impractical, it is often the case for older consoles that many thousands of games can be distributed together as a collection. Larger games are often distributed one by one.