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Bit Rot is a severe problem that will sooner or later plague every single prototype cartridge in existance. For a long time, collectors who own prototypes have not believed that there was any danger inherently existant in EPROMS. However, this simply is not the case. EPROMS were not a storage medium designed for permanent data storage - much like the media in floppy disks, VCR Tapes, and cassette tapes were all discovered to be much later, after time passed and the magnetic media in all the mentioned storage devices had begun to degrade. However, unlike these other media devices, when the data in EPROMS begin to degrade, there is no fuzzy movie left, no hissing song on the tape, or most of the files of the floppy disk remaining. Once the data on an EPROM has degraded - IT IS GONE. I will leave my opinions out of this page - while I do believe in public prototype dump release, I hope after reading this that whichever prototype owner who has not had their prototype cartridge dumped will at least get their games dumped privately if they do not wish to release them to the public.
Now, in order to explain bit rot, you have to take a look at the media that most prototypes are stored on. Above, are the two different kind of chips that are commonly found inside of game cartridges. On the right, you have an average run-of-the-mill ROM chip. These are the chips that are found in the games on the store shelves (or, that were on the store shelves in any case). This type of chip does not suffer from bit rot because they are not erasable, and are programmed in a different way than EPROMs. The EPROM, pictured on the left, are the type of chips used in nearly all prototypes. Normally, the window on the ROM chip pictured on the left would be covered by a sticker, to prevent accidental erasure as well as slow down bit rot, and of course, to know what is stored on that particular chip. An EPROM is arranged into individual memory cells which can store data - a "1" if not programmed, and a "0" if it is programmed. This will come into play later. The data programmed onto the chip is stored on the "gate" of a transistor inside of the EPROM. In order to program the EPROM, electrons are injected into the "gate," where they are captured. Until the EPROM's window is exposed to UVb light (or shorter wavelength), which allows the electrons to escape the gate, the data is held in the cells. While the captured electrons in the gates of the EPROM transistors provide the means of programming the chip, these same electrons are the very reason that bit rot happens. The root of the problem is the electrons that make up the data. While EPROMs are designed to capture these electrons and hold them, no insulation is perfect. Over time, regardless of how carefully the chip was handled and kept in a stable environment, the electrons will slowly leak out of the chip. As these electrons leak out of the gates that held them, the cells in the EPROM will revert from the "0" state (programmed) to the "1" state (unprogrammed). As more cells go bad in the EPROM, more and more of the program data that it contained is lost. This ladies and gentleman, is Bit Rot.
So is every EPROM due to die an instant death? Of course not - this is a situation that will eventually happen to every EPROM, but there are many factors involved in how long an EPROM will last. Most datasheets for EPROMs specify a minimum 10 years of guaranteed programming lifetime, however several factors can shorten the life of the data programmed onto an EPROM. Exposure to heat and ultraviolet light will decrease the life of an EPROM. A well cared for (or, at least non-abused) can last upwards of 25 years - however, let me present a small piece of evidence to you all. Above and below this paragraph are pictures from both a good Power Pad Test Cart as well as one that has succumbed to Bit Rot. This makes a very good example since the Program (PRG) EPROM is still intact, but the Character (CHR) EPROM has bit rotted. Above is what this game appears on the screen as, and below is the character tile dump from the dumped binaries of the games. Notice the corruption on the graphics. Would you like the prototype that you've spent a great deal of money on end up like this? Of course not. However, realize that this particular cart is around 14 years old - most Atari, Coleco, Intellivision, and many others are well over 25 years old - its the luck of the draw when it comes to bit rot - it can happen any time. Also remember that individual cells on an EPROM cannot be reprogrammed - once a cell goes bad, in order to replace it the whole EPROM will need to be erased and reprogrammed, losing all data that is currently stored on it.
The best defense, and the best way to protect your expensive investment is to get yourself a dump of the EPROMs in question. This way, if anything ever happens to the cart, such as the inevitable bit rot, or any other natural disaster resulting in the destruction of the cart, the data is NOT lost forever. The binary read of the data still exists. Contrary to some rumors as well, the dumping process, when done by a reputable dumper will not endanger the prototype in any way, and if there is any danger (example: The Pro Action Replay for the NES with data stored on battery-backed RAM, not EPROMs) you will be informed before anything is done. Ask around the internet - there are many reputable dumpers that will get your data protected for you. See our links page or email me and I can get you in contact with someone to dump your cartridges if you so choose. If you decide against having dumps made of your cartridges, please remember that bit rot will set in sooner or later, and there is nobody holding a gun to your head to release the ROM images even after their dumping. Please consider getting your data backed up sooner rather than later, because you never know when Bit Rot is going to set in and take it all away from you... Special thanks for this article go out to Kevin "Kevtris" Horton for providing the EPROM and ROM pics, the bit rotted dump of the Power Pad Test Cart, as well as explaining the concept of bit rot in detail to me. The original log explaining bit rot is here just in case I screwed up the explination. |
