Symbolics - History - Ivory and Open Genera

Ivory and Open Genera

In the late 1980s (2 years later than planned), the Ivory family of single-chip Lisp Machine processors superseded the G-Machine 3650, 3620, and 3630 systems. The Ivory 390k transistor VLSI implementation designed in Symbolics Common Lisp using NS, a custom Symbolics Hardware Design Language (HDL), addressed a 40-bit word (8 bits tag, 32 bits data/address). Since it only addressed full words and not bytes or half-words, this allowed addressing of 4 Gigawords (GW) or 16 gigabytes (GB) of memory; the 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 x 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 a 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.