AMD Am29000

The AMD Am29000, often simply 29k, was a popular family of 32-bit RISC microprocessors and microcontrollers developed and fabricated by Advanced Micro Devices (AMD). They were, for a time, the most popular RISC chips on the market, widely used in laser printers from a variety of manufacturers. In late 1995 AMD dropped development of the 29k because the design team was transferred to support the PC side of the business. What remained of AMD's embedded business was realigned towards the embedded 186 family of 80186 derivatives. The majority of AMD's resources were then concentrated on their high-performance, desktop x86 clones, using many of the ideas and individual parts of the latest 29k to produce the AMD K5.

The 29000 evolved from the same Berkeley RISC design that also led to the Sun SPARC and Intel i960. One "trick" used in all of the Berkeley-derived designs is the concept of register windows, a technique used to speed up procedure calls significantly. The basic idea is to use a large set of registers as a stack, loading local data into a set of registers during a call, and marking them "dead" when the procedure returns. Values being returned from the routines would be placed in the "global page", the top eight registers in the SPARC (for instance). It is interesting to note that the competing early RISC design from Stanford University, the Stanford MIPS, also looked at this concept but decided that improved compilers could make more efficient use of general purpose registers than a hard-wired window, something that has proven true over the years.