increase in address space reflected the growth of programs and data as semiconductor memory and disk space became cheaper. The Ivory processor had 8 bits of ECC attached to each word, so each word fetched from external memory to the chip was actually 48 bits wide. Each Ivory instruction was 18 bits wide and two instructions plus a 2-bit CDR code and 2-bit Data Type were in each instruction word fetched from memory. Fetching two instruction words at a time from memory enhanced the Ivory's performance. Unlike the 3600's microprogrammed architecture, the Ivory instruction set was still microcoded, but was stored in a 1200 × 180-bit ROM inside the Ivory chip. The initial Ivory processors were fabricated by VLSI Technology Inc in San Jose, California, on a 2 µm CMOS process, with later generations fabricated by Hewlett Packard in Corvallis, Oregon, on 1.25 µm and 1 µm CMOS processes. The Ivory had a stack architecture and operated a 4-stage pipeline: Fetch, Decode, Execute and Write Back. Ivory processors were marketed in stand-alone Lisp Machines (the XL400, XL1200, and XL1201), headless Lisp Machines (NXP1000), and on add-in cards for Sun Microsystems (UX400, UX1200) and Apple Macintosh (MacIvory I, II, III) computers. The Lisp Machines with Ivory processors operated at speeds that were between two and six times faster than a 3600 depending on the model and the revision of the Ivory chip. The Ivory instruction set was later emulated in software for microprocessors implementing the 64-bit Alpha architecture. The "Virtual Lisp Machine" emulator, combined with the operating system and software development environment from the XL machines, is sold as Open Genera. Sunstone Sunstone was a processor similar to a reduced instruction set computer (RISC), that was to be released shortly after the Ivory. It was designed by Ron Lebel's group at the Symbolics Westwood office. However, the project was canceled the day it was supposed to tape out. Endgame As quickly as the commercial AI boom of the mid-1980s had propelled Symbolics to success, the AI Winter of the late 1980s and early 1990s, combined with the slowdown of the Ronald Reagan administration's Strategic Defense Initiative, popularly termed Star Wars, missile defense program, for which the Defense Advanced Research Projects Agency (DARPA) had invested heavily in AI solutions, severely damaged Symbolics. An internal war between Noftsker and the CEO the board had hired in 1986, Brian Sear, over whether to follow