Mask work copyright

The United States Library of Congress defines a mask work as "a series of related images, however fixed or encoded, having or representing the predetermined, three-dimensional pattern of metallic, insulating, or semiconductor material present or removed from the layers of a semiconductor chip product, and in which the relation of the images to one another is such that each image has the pattern of the surface of one form of the semiconductor chip product" (Copyright Office Form MW, http://www.loc.gov/copyright/forms/formmw.pdf).

According to 17 USC chapter 9 (http://www4.law.cornell.edu/uscode/17/ch9.html), semiconductor mask work copyrights last only ten years (in contrast to effectively perpetual copyright on most other works) and are not subject to the typical backup exemptions that 17 USC 117 provides for computer software.

The correct symbol used in a mask work's copyright notice is Ⓜ (M enclosed in a circle; Ⓜ) or *M*, not (M) in parentheses as your web browser may render it.

Software for a cartridge-based video game console normally is granted two distinct copyrights: a Form TX copyright on the program (registered by sending in source code) or a Form PA copyright on the visual displays generated by the work (depending on whether code or art dominates a program), and a Form MW copyright on the ROM that contains the binary. The lack of backup exemption means that Nintendo can go after sites that carry ROM dumps copyright 1991 or later (Super NES, Nintendo 64, Game Boy), but ROM sites hosting mostly software for older consoles may fall under normal copyright law's fair use, library (17 USC 108), and backup exemptions. Of course, if you have [developed your own software for NES]? and have released it under a free software license, this doesn't apply.

Could this explain why Nintendo waited until lawmakers passed the DMCA and foreign counterparts before releasing a game console that used media other than cartridges?

Wikipedia does not provide legal advice.