It's interesting to look at the early issues of the official TeX publication Tugboat[1]. The first version of TeX, TeX78, written in the SAIL language was just

It's interesting to look at the early issues of the official TeX publication Tugboat[1]. The first version of TeX, TeX78, written in the SAIL language was just out and there was a concerted effort to produce a more portable version in Pascal, TeX82 (IIRC already known under that name during production). The first issues of Tugboat then contained several reports about early TeX being ported to various architectures. That often meant rewriting the whole program, as basically no other system besides Knuth's "native" time-sharing OS had SAIL. So there was a port to a (Z80-based) Unix, someone rewriting parts in Fortran, etc. If they were tied to a specific backend/printer, there wasn't even a need to port Metafont. TeX was relatively small. That often gets lost in contemporary huge LaTeX distributions. [1]: https://www.tug.org/tugboat/ https://www.tug.org/tugboat/