page_title: Symbolics
section_title: The 3600 series
hierarchical_section_title: Symbolics / History / The 3600 series
caption_attribution_description: English: Ports on the back of a Symbolics 3600. This machine was used as a front-end to a Connection Machine supercomputer. From the collection of the RCS/RI.
context_page_description: Symbolics is a defunct computer manufacturer Symbolics, Inc., and a privately held company that acquired the assets of the former company and continues to sell and maintain the Open Genera Lisp system and the Macsyma computer algebra system.
  The symbolics.com domain was originally registered on March 15, 1985, making it the first .com-domain in the world. In August 2009, it was sold to napkin.com Investments.
context_section_description: In 1983, a year later than planned, Symbolics introduced the 3600 family of Lisp machines. Code-named the "L-machine" internally, the 3600 family was an innovative new design, inspired by the CADR architecture but sharing few of its implementation details. The main processor had a 36-bit word (divided up as 4 or 8 bits of tags, and 32 bits of data or 28 bits of memory address). Memory words were 44 bits, the additional 8 bits being used for error-correcting code (ECC). The instruction set was that of a stack machine. The 3600 architecture provided 4,096 hardware registers, of which half were used as a cache for the top of the control stack; the rest were used by the microcode and time-critical routines of the operating system and Lisp run-time environment. Hardware support was provided for virtual memory, which was common for machines in its class, and for garbage collection, which was unique.
  The original 3600 processor was a microprogrammed design like the CADR, and was built on several large circuit boards from standard TTL integrated circuits, both features being common for commercial computers in its class at the time. Central processing unit (CPU) clock speed varied depending on which instruction was being executed, but was typically around 5 MHz. Many Lisp primitives could be executed in a single clock cycle. Disk input/output (I/O) was handled by multitasking at the microcode level. A 68000 processor (termed the front-end processor, (FEP)) started the main computer up, and handled the slower peripherals during normal operation. An Ethernet interface was standard equipment, replacing the Chaosnet interface of the LM-2.
  The 3600 was roughly the size of a household refrigerator. This was partly due to the size of the processor (the cards were widely spaced to allow wire-wrap prototype cards to fit without interference) and partly due to the size of disk drive technology in the early 1980s. At the 3600's introduction, the smallest disk that could support the ZetaLisp software was 14 inches (360 mm) wide (most 3600s shipped with the 10½-inch Fujitsu Eagle). The 3670 and 3675 were slightly shorter in height, but were essentially the same machine packed a little tighter. The advent of 8 inches (200 mm), and later 5 ¹⁄₄ inches (130 mm), disk drives that could hold hundreds of megabytes led to the introduction of the 3640 and 3645, which were roughly the size of a two-drawer file cabinet.
  Later versions of the 3600 architecture were implemented on custom integrated circuits, reducing the five cards of the original processor design to two, at a large manufacturing cost savings and with performance slightly better than the old design. The 3650, first of the G machines, as they were known within the company, was housed in a cabinet derived from the 3640s. Denser memory and smaller disk drives enabled the introduction of the 3620, about the size of a modern full-size tower PC. The 3630 was a fat 3620 with room for more memory and video interface cards. The 3610 was a lower priced variant of the 3620, essentially identical in every way except that it was licensed for application deployment rather than general development.
  The various models of the 3600 family were popular for artificial intelligence (AI) research and commercial applications throughout the 1980s. The AI commercialization boom of the 1980s led directly to Symbolics' success during the decade. Symbolics computers were widely believed to be the best platform available for developing AI software. The LM-2 used a Symbolics-branded version of the complex space-cadet keyboard, while later models used a simplified version (at right), known simply as the Symbolics keyboard. The Symbolics keyboard featured the many modifier keys used in Zmacs, notably Control/Meta/Super/Hyper in a block, but did not feature the complex symbol set of the space-cadet keyboard.
  Also contributing to the 3600 series' success was a line of bit-mapped graphics color video interfaces, combined with extremely powerful animation software. Symbolics' Graphics Division, headquartered in Westwood, Lo
caption: 3600 ports, with Connection Machine interface
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