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.

History

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 Symbolics machine was actually competitive against many commercial super mini computers, but it was never adapted or sold for conventional purposes.

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.

BBN developed its own Lisp Machine, called Jericho, which ran a version of Interlisp. It was never marketed.

A UK company, Racal-Norsk, attempted to repurpose Norsk Data superminis as microcoded Lisp Machines, running Symbolics' Zetalisp software.

There were several attempts by Japanese manufacturers to enter the Lisp Machine market, including the Fujitsu Facom-alpha mainframe co-processor (which was actually marketed as early as 1978), and several university research efforts that produced working prototypes. There are even rumors of a Sony hand-held Lisp Machine prototype.

As the "PC revolution" gathered steam and swept away the minicomputer and workstation manufacturers, ordinary desktop PCs soon were able to run Lisp programs even faster than Lisp machines, without the use of special purpose hardware, and most Lisp Machine manufacturers went out of business by the early 90s. Besides Xerox, Symbolics is the only Lisp Machine company still operating today, selling the Open Genera Lisp Machine software environment as well as the Macsyma computer algebra system.

In the late 90s, there were plans by Sun Microsystems and other companies to build language-specific computers for Java, similar in concept and execution to the Lisp machines, but none of the ventures ever produced any products.

External Links

• Jaap Weel's Lisp Machine Webpage (http://www.ugcs.caltech.edu/~weel/lispm.shtml)
• Ralf Möller's Symbolics Lisp Machine Museum (http://www.sts.tu-harburg.de/~r.f.moeller/symbolics-info/symbolics.html)
• Symbolics (http://www.symbolics.com/)
• CADR documentation (http://www.bitsavers.org/pdf/mit/cadr)
• CADR simulation (http://www.heeltoe.com/retro/cadr)
• L-machine simulation (http://www.heeltoe.com/retro/lispm/l-machine.html)