Abstract

ROM hacking for the purposes of this document will be defined as the the editing of ROM images and ISO images (ISO being the traditional term for images of optical media) with the intent of changing how underlying game code or the assets of it function in a useful way. Simply changing sections of an image without rhyme or reason is not ROM hacking as ROM hacking is usually the end result of a measure of reverse engineering.

The following document covers ROM hacking methods with a focus upon GBA and DS hacking techniques, but with occasional asides into the other home consoles. Broadly speaking there are two main methods of producing useful ROM hacks with the most effective but initially most complex being the traditional definition of ROM hacking (sometimes called low level ROM hacking) where formats and methods of interaction are reverse engineered before being altered and extended. The other type, most often associated with the Pokemon franchise but far from exclusive to it, revolves around using premade tools to change games extensively in a manner closer to more traditional text, graphics and level editing, however with the use of such tools there can be very extensive hacks created in a short period of time by those with minimal knowledge of the underlying processes. It should also be noted that in more recent times a third, and possibly fourth, type have arisen, especially on the DS, where developers are commonly seen to use formats from the SDK or some other development library that brings aspects of low level hacking and tool driven hacking together by allowing rapid decoding of formats and exporting them before conducting lower level operations to insert the modifications and the potential fourth candidate has been seen in programs allowing plugins or scripts to be created using simple often text or XML a like formats to do similar things.

With regards to premade tools they will not be a focus of this document, although if ones exist they might be mentioned.

Categorisation can occur several more times with one in particular forming the outline of this document. In short the four main categories of ROM hacking seen today are graphics editing, text editing, multimedia editing and game logic (which includes assembly coding). Each of those can be subdivided at least one more time, to say nothing of each of those drawing from the other categories or having elements cross over; for instance in many puzzle games the text is encoded as regular graphics formats. The other categorisation, in this case of the hacks themselves, that will be thrown about a bit is translation, improvement, alteration and spoof. Such categorisations are of limited use for this document as they can all display very advanced techniques in each of the previously discussed categorisations.

This document is largely intended for those that do not know much about ROM hacking or low level computing beyond maybe the command line interface, that said those at all levels of computing and ROM hacking knowledge should be able to get something from this and it is hoped that the focus on the GBA and DS will aid those looking to transfer from other consoles.