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Lisp machine

Lisp machines were general purpose computers designed (often with hardware support) to efficiently run Lisp as their main language. In a sense, they were the first commercial single-user workstations.


Artificial intelligence computer programs of the 1960s and 1970s required what was then considered a huge amount of computer power, as measured in processor time and memory space. At first, the cost of such computer hardware meant that it had to be shared among many users. But as integrated circuit technology shrank the size and cost of computers in the 1960s and early 1970s, and the memory requirements of AI programs started to exceed the address space of the most common research computer, the DEC PDP-10, researchers considered a new approach: a computer designed specifically to run large artificial intelligence programs, and tailored to the semantics of the Lisp programming language. To keep the operating system (relatively) simple, these machines would not be shared, but would be dedicated to a single user.

In 1974 Richard Greenblatt at MIT started the MIT Lisp Machine Project. The first machine was called CONS (named after the list construction operator in Lisp); it was subsequently improved into a version called CADR (a pun; in Lisp, the CADR function returns the second element of a list). The CADR was later commercialized by Symbolics as the LM-2, by Lisp Machines, Inc (LMI) as the LMI-CADR. Both Symbolics and LMI developed second-generation products based on the CADR: the Symbolics 3600 and the LMI LAMBDA. The 3600 expanded on the CADR by widening the machine word, expanding the address space, and adding hardware to accelerate certain common functions that were implemented in microcode on the CADR. The LMI-LAMBDA was compatible with the CADR (it could run CADR microcode), but there were hardware differences. Texas Instruments (TI) joined the fray when it licensed the LMI-LAMBDA design and produced its own variant, the TI Explorer.

Symbolics continued to develop the 3600 family and produced the Ivory, a VLSI implementation of the Symbolics architecture. TI shrunk the Explorer into silicon as the MicroExplorer. LMI abandoned the CADR architecture and developed its own K-Machine, but LMI went bankrupt before the machine could be brought to market.

These machines had hardware support for various primitive lisp operations (data type testing, CDR coding) and also hardware support for incremental garbage collection. They ran large Lisp programs very efficiently.

The MIT-derived Lisp machines ran a Lisp dialect called ZetaLisp, descended from MIT's MacLisp. The operating systems were written from the ground up in Lisp.

Meanwhile, Xerox PARC developed machines which were designed to run InterLisp as well as other languages such as Smalltalk. These included the Xerox 1100, aka "Dolphin"; the Xerox 1132, aka "Dorado"; the Xerox 1108, aka "Dandelion"; and the Xerox 1109, aka "Dandetiger"; and the Xerox 6085, aka "Daybreak". The Xerox machines were a commercial failure, but they did influence the creation of Apple Computer's Macintosh.

All these products are history, due to the speed of evolution of so-called "commodity hardware" (that is, generic computers based on microprocessor chips) and advances in compiler technology. As the "PC revolution" gathered steam and swept away even the minicomputer manufacturers, ordinary desktop PCs soon were able to run Lisp programs even faster than Lisp machines, without the use of special purpose hardware.