[TUHS] Re: mental architecture models, Anyone ever heard of teaching a case study of Initial Unix?

See https://www.cs.tufts.edu/~nr/cs257/archive/ronald-brender/bliss.pdf C allowed writing Unix with a limited amount of assembly code, but CMU's original BLISS-10 was designed to write an operating system with *no* outside assembly code.  Features like the 'MACHOP' (machine operation) builtin function made use of  the orthogonality of the PDP-10 instruction format to execute machine-specific instructions in-line.  (cf. the 'asm' extensions in some implementations of C.)  The PDP-10's 36-bit word allowed single-precision floating point numbers to fit in machine words, so it had infix operators for both integer and single-precision floating point operations (which I presume were adequate for an operating system). When DEC chose an implementation language, they knew about C but it had not yet escaped from Bell Labs.  PL/I was considered, but there were questions of whether or not it would be suitable for a minicomputer.  On the other hand, by choosing BLISS, DEC could start with the BLISS-11 cross compiler running on the PDP-10, which is described in https://en.wikipedia.org/wiki/The_Design_of_an_Optimizing_Compiler BLISS-11 and DEC's Common BLISS had changes necessitated by different word lengths and architectures, including different routine linkages such as INTERRUPT, access to machine-specific operations such as INSQTI, and multiple-precision floating point operations using builtin functions which used the addresses of data instead of the values. In order to port VMS to new architectures, DEC/HP/VSI retargeted and ported the BLISS compilers to new architectures. What I find amazing is that they also turned the VAX MACRO assembly language (in which some of the VMS operating system was written) into a portable implementation language by 'compiling' the high-level CISC VAX instructions (and addressing modes) into sequences of RISC instructions.  I believe that this is similar to how modern CPU chips dynamically translate x86_64 instructions (or whatever) to an internal RISC format. - Aron (Disclaimer: I worked at DEC for a long time and VSI for a short time, but I wasn't responsible for the above work.) On 7/6/24 17:32, Charles H Sauer (he/him) wrote: