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0 pointsducktective1y ago0 comments

>On Lisp Machine, Zmacs ran in a multi-threaded Lisp

I wonder what the processing architecture of those Lisp machines were like. Did their "cpu"(?) had special circuitry for implementing lists, CAR and CDR? Was this multi-threaded-ness something built-in in hardware?

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amszmidt1y ago

There is nothing special about CAR and CDR on the Lisp Machine, which should be considered a virtual machine for all intents and purposes that was implemented in microcode.

Multi processing was implemented mostly in Lisp, but stack group handling (how the system manages "threads") was done in microcode.

The hardware for the CADR is very simple, and has no knowledge of Lisp or the Lisp Machine.

lispm1y ago

> Did their "cpu"(?) had special circuitry for implementing lists, CAR and CDR?

It was implemented in Microcode on the CPU.

> Was this multi-threaded-ness something built-in in hardware?

Some. The process scheduler was written in Lisp. See for an early example on the MIT Lisp Machine: https://github.com/mietek/mit-cadr-system-software/blob/mast...

dokyun1y ago

I think you should clarify that the Lisp machines (at least the early ones that you speak of) were not 'multi-threaded' in the sense of multiprocessing--the only multiprocessing they did was running independent Lisp systems on each of their processors, if they had more than one.

lispm1y ago

From the 1981 4th edition Lisp Machine Manual, page 428ff

> 25. Processes

> The Lisp Machine supports multi-processing; several computations can be executed "concurrently" by placing each in a separate process. A process is like a processor, simulated by software. Each process has its own "program counter", its own stack of function calls and its own special-variable binding environment in which to execute its computation. (This is implemented with stack groups, see chapter 12, page 163.)

These computers could send/receive network traffic, handle the GUI, read from disk, while the user would have processes for each application and window.

On my mid 1980s Symbolics 3640 I could compile a Lisp application from scratch in a Lisp REPL for half an hour, while I was using Zmacs to edit code. The practical limitations were CPU speed, memory size, disk speed and the Garbage collector. A full GC would halt everything else. Better incremental GCs helped a lot.

In GNU Emacs last I tried I could not use two IELM repls executing Lisp code at the same time. One would block the rest of GNU Emacs Lisp code.

amszmidt1y ago

There is a bit to much simplification here, and confusing terminology going on here. Lisp Machines did not have "processes" (as in, Unix processes); a Lisp Machine process just a function - with some special properties.

The Lisp Machine only had one processor for the Lisp Machine, and it did absolutely support multi-processing and multi-threading.

A good explanation can be found in the Lisp Machine manual:

  https://tumbleweed.nu/r/lm-3/uv/chinual.html#Processes
  https://tumbleweed.nu/r/lm-3/uv/chinual.html#Stack-Groups

Which is also where all current work on the MIT Lisp Machine is being done. :-)

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amszmidt1y ago

There is nothing special about CAR and CDR on the Lisp Machine, which should be considered a virtual machine for all intents and purposes that was implemented in microcode.

Multi processing was implemented mostly in Lisp, but stack group handling (how the system manages "threads") was done in microcode.

The hardware for the CADR is very simple, and has no knowledge of Lisp or the Lisp Machine.

lispm1y ago

> Did their "cpu"(?) had special circuitry for implementing lists, CAR and CDR?

It was implemented in Microcode on the CPU.

> Was this multi-threaded-ness something built-in in hardware?

Some. The process scheduler was written in Lisp. See for an early example on the MIT Lisp Machine: https://github.com/mietek/mit-cadr-system-software/blob/mast...

dokyun1y ago

lispm1y ago

From the 1981 4th edition Lisp Machine Manual, page 428ff

> 25. Processes

These computers could send/receive network traffic, handle the GUI, read from disk, while the user would have processes for each application and window.

In GNU Emacs last I tried I could not use two IELM repls executing Lisp code at the same time. One would block the rest of GNU Emacs Lisp code.

amszmidt1y ago

The Lisp Machine only had one processor for the Lisp Machine, and it did absolutely support multi-processing and multi-threading.

A good explanation can be found in the Lisp Machine manual:

  https://tumbleweed.nu/r/lm-3/uv/chinual.html#Processes
  https://tumbleweed.nu/r/lm-3/uv/chinual.html#Stack-Groups

Which is also where all current work on the MIT Lisp Machine is being done. :-)

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