> i don't think it's entirely accurate to describe it as 'a pascal machine'
yes
it would only be accurate, when one looks at BOTH the CPU and the microcode.
The Xerox Interlisp-D machine was a Lisp Machine with the specific microcode. It was a Smalltalk machine and a Mesa machine - each with their microcode.
The original MIT Lisp machine was also microcoded, though I don't know other Microcode than the one for Lisp. The early Symbolics Lisp Machines were also microcoded, but again only for the Lisp OS, with the microcode evolving over time to support features of Common Lisp, Prolog and CLOS.
There were complaints that the Microcode on the Lisp Machines was very complex, which contributed to the death of the machines. For example here is an interview with Keith Diefendorff, who was also architect for the TI Explorer Lisp Machine. In his interview he talks about the Explorer Project and the Microcode topic: https://www.youtube.com/watch?v=9la7398ruXQ
The MIT Lisp Machine microcode feels like writing in a modern 3-address RISC instruction set to me. I see a lot of reluctance to modifying the source in old mailing lists, maybe everyone was told that it was too hard so didn't try.
EDIT: An example: The CADR has a nice API from Lisp to the CHAOSNET hardware, the microcode wakes up a stack group (thread) and passes it a buffer to process. Later machines had Ethernet but there isn't any microcode support for the hardware, Lisp code just polls the status of the ethernet controller and copies packets around a byte at a time. The microcode buffer handling routines for CHAOSNET could have been reused for Ethernet.
Issue with the CADR (and Lambda ..) microcode isn't that it is hard to modify, it is that there is a very deep snake pit, and lots of complex interaction between the microcode and the Lisp Machine.
The CADR already had support for (pre-)Ethernet via microcode very early (~1979) and did it more or less the same way as for Chaosnet. The Lambda I think modified this quite heavily though to something else ...
yes
it would only be accurate, when one looks at BOTH the CPU and the microcode. The Xerox Interlisp-D machine was a Lisp Machine with the specific microcode. It was a Smalltalk machine and a Mesa machine - each with their microcode.
The original MIT Lisp machine was also microcoded, though I don't know other Microcode than the one for Lisp. The early Symbolics Lisp Machines were also microcoded, but again only for the Lisp OS, with the microcode evolving over time to support features of Common Lisp, Prolog and CLOS.
There were complaints that the Microcode on the Lisp Machines was very complex, which contributed to the death of the machines. For example here is an interview with Keith Diefendorff, who was also architect for the TI Explorer Lisp Machine. In his interview he talks about the Explorer Project and the Microcode topic: https://www.youtube.com/watch?v=9la7398ruXQ