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36bits for lisp was specific to PDP-6/10 not anything else. And Lisp in turn took its "memory word is a cons cell because you can fit two addresses in one word
by p_l 3y ago
36bits for lisp was specific to PDP-6/10 not anything else.
And Lisp in turn took its "memory word is a cons cell because you can fit two addresses in one word" from a 36bit IBM scientific computer with 15 bit addressing.
- lispm 3y agoThe Symbolics 3600 series were also 36bit machines. Later the Symbolics Ivory microprocessor then was a 40bit cpu.
- p_l 3y agoyes, but in both cases the motivation was to have 32bit fixnums and addresses and thus word size was extended with extra bits for tags, unlike the predecessor design of CADR which used 32bit bus and had to stuff tags and fixnum/addresses together - resulting in 24bit fixnum/address space, or 3 8bit characters stuffed into each word, plus 4 bits of tags. TI Explorer later updated CADR/LMI design to use 25bit fixnum/address and 3bit mandatory tags. For people who don't know: Tag space included both CDR-coding (compression mechanism for linked lists), datatype tags, as well as formed portion of the instructions if the word contained instructions - on 3600 and Ivory each word could contain 1 or 2 instructions.