The creators of the AS/400 originally planned to use the name System/40, but IBM had adopted a new product nomenclature around the same time, which led to the Application System/400 name. Firstly, IBM began prefixing "System" in product names with words to indicate the intended use or target market of the system (e.g. Personal System/2 and Enterprise System/9000). Secondly, IBM decided to reserve one and two digit model numbers for personal systems (e.g. PS/2 and PS/55), three digit numbers for midrange systems (e.g. AS/400) and four digit numbers for mainframes (e.g. ES/9000). The reassignment of two digit model numbers from midrange systems to personal systems was to prevent the personal systems from running out of single-digit numbers for new products. The move to PowerPC In 1990, IBM Rochester began work to replace the AS/400's original System/38-derived 48-bit CISC processors with a 96-bit architecture known as C-RISC (Commercial RISC). Rather than being a clean-slate design, C-RISC would have added RISC-style and VLIW-style instructions to the AS/400's processor, while maintaining backwards compatibility with the System/370-style Internal Microprogrammed Interface (IMPI) instruction set and the microcode used to implement it. In 1991, at the request of IBM president Jack Kuehler, a team under the leadership of Frank Soltis delivered a proposal to adapt the 64-bit PowerPC architecture to support the needs of the AS/400 platform. Their extensions to the PowerPC architecture, known as Amazon (and later as PowerPC AS), were approved by IBM management instead of the C-RISC design for development into the next AS/400 processor architecture. These extensions include support for tagged memory, as well as assistance for decimal arithmetic. IBM initially attempted to create a single PowerPC implementation for both AS/400 and high-end RS/6000 systems known as Belatrix. The Belatrix project proved to be too ambitious, and was cancelled when it became apparent that it would not deliver on schedule. Instead, a pair of AS/400-specific processors were designed at IBM Endicott and IBM Rochester, known as Cobra (for low end systems) and Muskie (for high end systems) respectively. These became the initial implementations of the IBM RS64 processor line. The RS64 series continued to be developed as a separate product line at IBM until the POWER4 merged both the RS64 and POWER product lines together. Despite the move from IMPI to an entirely different processor architecture, the AS/400's Technology Independent Machine Interface (TIMI) mostly hid the changes from users and applications, and