1.3 Patching and patch making

ROM hackers change ROM images, copyright lengths being what they are it means such things are copyrighted code. Even edited code still has protections so the differences between the versions are found and made into a patch file, such a thing will also have the very nice bonus of tending to be far smaller and easier to transmit. Patch files then allow someone to take the original ROM, apply the patch to turn it into your changed version and then play it. As with most concepts you can use a computer to help out and, also like most concepts, there many methods by which you can create and apply patches. However unlike most other times where you need to decide between competing formats there is more to it than token differences and vendor lock in. Each type is linked to the best example/implementation at time of writing with a couple more at the end if there are others worth noting.

• IPS. The original ROM hacking patching method of choice. It is a truly basic format (the basic form contains a magic stamp/value, a list of patches to apply (which consist of a location, length and payload) and a signal for the end of the file) although there are a few custom versions that are not widely supported. It can not handle location changes which is not a problem for older consoles but with consoles that have filesystems (which is to say most optical media using and post GBA consoles) it is a dealbreaker. It is also limited to files of 16 megabytes in size or less, again this is not a problem on older consoles but even the GBA allowed code up to 32 megabytes to be run.
• UPS. Made as a direct successor to IPS it has found some use in older consoles and later GBA patches but came a bit too late and the patching methods below had stolen the spotlight. Upset, Tsukuyomi UPS and NUPS are all good tools for UPS.
• PPF. Made originally to patch PS1 games (Playstation Patching Format being the longer form) it went through a few revisions and as such some are wary, however it saw some use on the Wii and continues to kick around. Size limits are not really a problem (it is unknown what the upper limit is) and shifts are handled OK. PPF-O-Matic is a nice GUI patching program and the original PPF program should provide a nice multiplatform patching and patch making alternative.
• Xdeltaand BSDiff. Both general patching formats (indeed they tend to position themselves as rival formats) that got used for the DS and newer consoles (ROM hackers have tended to favour Xdelta where BSDiff saw more use in the form of Scene trainers and patches). Shifts are handled well enough (although they might not be perfect) and sizes are not likely to get to a limit any time soon (although some implementations of BSDiff are rather low). Features some support for original file checking and hashing. The current version of Xdelta was linked but there is an older version that was used for a while and there have been some compatibility issues.
• Ninja. An earlier candidate to replace IPS and fell out of favour for various reasons. Some patches have been seen to use it and in many ways it works quite well.
• PAR2. Not a patching method per se and more of a corruption detection and data recovery format. Changed data is no different to corrupt data as far as it is concerned so can patch programs though it has some trouble with data shifts. Better yet though assuming you have enough redundancy you can be certain your patch will make the original ROM into exactly what you need which is quite useful when there are various corrupt or otherwise modified dumps out in the wild (headers on SNES ROM files for instance).
• Custom. There were some other formats made for various things (Jump Super Stars for instance) and others aimed at more specific things (Fireflower is a patching format aimed at certain graphics hacks for instance) but those will not really be covered here. Some people decided to unpack the ISO/ROM files, patch those individually and build a ROM/ISO afterwards. This made for the smallest patch sizes, usually got around the issue of file relocation, made for some of the best compatibility with various ROM versions and the gave the option to have various options for the patch; a graphics translation might translate graphics that are for the most part decorative, rather than having to make an executive decision you can just make an option at the patch level. The main downside is that it might well be platform specific, require multiple batch files to be made or require runtimes to be installed. Can also help where files are encrypted or compressed and by making a patch you are still technically redistributing code that does not belong to you (encryption and compression looks like differences to a basic compare function).

Some people took this custom format concept a step further on the Wii and some other consoles by making a kind of jump loader using a dashboard/menu level console hack to apply a patch to a game’s data when it was held in memory. This also had the added bonus of allowing those with the original game and an otherwise unhacked Wii to play the hacked game. Nintendo would do a similar thing to patch a bug in Wii sports resort as the Wii lacks a real patch management feature like the 360 and PS3.