6
• Static translation involves reading in the whole of the source program and translating it
for the target system, producing a program that is executable on that system. However it
is not always possible to determine how a program will execute from a static analysis of
it. Branch instructions, for example, often depend on the contents of memory locations
which can only be determined at run-time [20].
• Dynamic translation works in much the same way as static translation but occurs while
executing the program. This allows it to account for branch and jump instructions and to
produce accurate code [20].
The NES is perhaps the most widely emulated console with a number of emulators already
available of varying quality. Writing a NES emulator remains a very challenging project,
requiring a detailed understanding of how the system works. A fairly comprehensive list of
available NES emulators can be found at [21] although many of these have been
discontinued. The basics of writing an emulator are described by [17] and [22], both of which
focus specifically on the NES.
1.4 Legal
Emulation is considered to be something of a legal grey area. Emulators are not illegal,
provided all the information used in the development is legally obtained and does not contain
any proprietary code. However, it is illegal to run any software which you do not own a
licence for.
Copying NES games is possible with the correct hardware. Such copiers dump the contents
of the game cartridges to a disk to enable access by a computer. There are a wide variety of
copiers, which function in different ways. Figure 1-3 shows ChameleonNES which copies the
contents of a cartridge to a PC via a USB port. Copyright law typically allows for a backup
copy to be made, however this does not apply to games stored on permanent semiconductor
chips such as those used by the NES. These copying devices are illegal.
Figure 1-3. ChameleonNES cartridge copier [23].
Most emulator users download games from the Internet since they do not have access to the
required copying hardware. These websites usually cover themselves with an agreement
that you can only download a file if you own the original game or if you will delete it within 24
hours. This may make the process look legal but, since the copies are illegal, it is clearly not.
Even if the law allowed for making a backup copy of a NES game, copies can only be made
and used by the original owner, so downloading files off the Internet would still be illegal.
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