A LISP machine

LISP is the second oldest computer-programming language still in active use. Our implementation is based on a powerful microprogrammed processor designed specifically for LISP. This processor supports a tagged macro-architecture; it manipulates items which have a built-in data-type field. The system supports several important new storage-management features, including a real-time garbage collector with hardware assist (using the basic algorithm of Baker). The software itself is written in LISP to a much larger extent than in previous systems. In fact, there are only two levels in which code is written: LISP and microcode. Among other things this improves the consistancy of system interfaces. The system design incorporates the personal computer philosophy. We believe the personal computer will predominate in the future since it is preferable to time-sharing in most cases and technological trends are greatly reducing its cost penality. In the case of very large programs, the personal computer can be cost-effective today, due to the phenomenon of thrashing encountered in time-sharing systems.