MHz version would "beat the pants off a 68000 in most applications", but any product using it would have to be compatible with the Apple II. Rumors spread about his work on an "Apple IIx". The IIx was said to have a 16-bit CPU, one megabyte of RAM, and better graphics and sound. "IIx" was the code name for Apple's first internal project to develop a next-generation Apple II based on the 65816. The IIx project, though, became bogged down when it attempted to include various coprocessors allowing it to emulate other computer systems. Early samples of the 65816 were also problematic. These problems led to the cancellation of the IIx project, but later, a new project was formed to produce an updated Apple II. This project, which led to the released IIGS, was known by various codenames while the new system was being developed, including "Phoenix", "Rambo", "Gumby", and "Cortland". There were rumors of several vastly enhanced prototypes built over the years at Apple but none were ever released. Only one, the "Mark Twain", has been revealed so far. The Mark Twain prototype (named for Twain's famous quote "The reports of my death are greatly exaggerated") was expected to have the "ROM 04" revision (although prototypes that have been discovered do not contain any new ROM code) and featured an 8 MHz 65C816, built-in SuperDrive, 2 MB of RAM, and a hard drive. Some design features from the unsuccessful Apple III lived on in the Apple IIGS, such as GS/OS borrowing elements from SOS (including, by way of ProDOS, the SOS file system), a unique keyboard feature for dual-speed arrow keys, and colorized ASCII text. Release Limited Edition ("Woz"-signed case) As part of a commemorative celebration marking the 10th anniversary of the Apple II series' development, as well as Apple Computer itself celebrating the same anniversary, a special limited edition was introduced at product launch. The first 50,000 Apple IIGSs manufactured had a reproduced copy of Wozniak's signature ("Woz") at the front right corner of the case, with a dotted line and the phrase "Limited Edition" printed just below it. Owners of the Limited Edition, after mailing in their Apple registration card, were mailed back a certificate of authenticity signed by Wozniak and 12 key Apple engineers, as well as a personal letter from Wozniak himself (both machine-reproduced). Because the difference between standard and Limited Edition machines were purely