Editing Lisp machine (section)

==Technical overview==

Initially the Lisp machines were designed as personal workstations for software development in Lisp. They were used by one person and offered no multi-user mode. The machines provided a large, black and white, bitmap display, keyboard and mouse, network adapter, local hard disks, more than 1 MB RAM, serial interfaces, and a local bus for extension cards. Color graphics cards, tape drives, and laser printers were optional.

The processor did not run Lisp directly, but was a [[stack machine]] with instructions optimized for compiled Lisp. The early Lisp machines used microcode to provide the instruction set. For several operations, type checking and dispatching was done in hardware at runtime. For example, only one addition operation could be used with various numeric types (integer, float, rational, and complex numbers). The result was a very compact compiled representation of Lisp code.

The following example uses a function that counts the number of elements of a list for which a predicate returns <code>true</code>.

<syntaxhighlight lang="lisp">
(defun example-count (predicate list)
  (let ((count 0))
    (dolist (i list count)
      (when (funcall predicate i)
        (incf count)))))
</syntaxhighlight>

The disassembled machine code for above function (for the Ivory microprocessor from Symbolics):

<syntaxhighlight lang="nasm">
Command: (disassemble (compile #'example-count))

  0  ENTRY: 2 REQUIRED, 0 OPTIONAL      ;Creating PREDICATE and LIST
  2  PUSH 0                             ;Creating COUNT
  3  PUSH FP|3                          ;LIST
  4  PUSH NIL                           ;Creating I
  5  BRANCH 15
  6  SET-TO-CDR-PUSH-CAR FP|5
  7  SET-SP-TO-ADDRESS-SAVE-TOS SP|-1
 10  START-CALL FP|2                    ;PREDICATE
 11  PUSH FP|6                          ;I
 12  FINISH-CALL-1-VALUE
 13  BRANCH-FALSE 15
 14  INCREMENT FP|4                     ;COUNT
 15  ENDP FP|5
 16  BRANCH-FALSE 6
 17  SET-SP-TO-ADDRESS SP|-2
 20  RETURN-SINGLE-STACK
</syntaxhighlight>

The operating system used [[virtual memory]] to provide a large address space. Memory management was done with garbage collection. All code [[ single address space operating system | shared a single address space]]. All data objects were stored with a tag in memory, so that the type could be determined at runtime. Multiple execution threads were supported and termed ''processes''. All processes ran in the one address space.

All operating system software was written in Lisp. Xerox used Interlisp. Symbolics, LMI, and TI used Lisp Machine Lisp (descendant of MacLisp). With the appearance of Common Lisp, Common Lisp was supported on the Lisp Machines and some system software was ported to Common Lisp or later written in Common Lisp.

Some later Lisp machines (like the TI MicroExplorer, the Symbolics MacIvory or the Symbolics UX400/1200) were no longer complete workstations, but boards designed to be embedded in host computers: Apple [[Macintosh II]] and [[Sun-3]] or [[Sun-4]].

Some Lisp machines, such as the Symbolics XL1200, had extensive graphics abilities using special graphics boards. These machines were used in domains like medical image processing, 3D animation, and CAD.