but already in the early 1960s with mainframe based typesetting systems I'm well aware of that. But I think your typical small publisher - and except for IBM, DEC, etc. most software publishers were small in the 1970s and early 1980s - couldn't afford to make use of a mainframe typesetting system.

I agree. The people who were actually doing the work (i.e. operators etc.) very often got manuals which were produced on a drum printer and were likely to be updated on a regular basis, and where some important fragment needed to be reproduced for somebody who expected "a glossy" it would be directly derived from drum printer (or Teletype, Flexowriter etc.) output.

@Raffzahn Maybe I wasn't clear but I qualified "source code in non typewritten computer manuals and books" to mean I wasn't referring to all manuals and books, just those where code wasn't already monospace.

The PET Computer User Manual that you linked uses a proportional font for its examples. Look at the word PRINT in any example that contains it and it is clear that it is using a proportional font. It's PRINT not PRINT

@PaoloAmoroso Not sure what you mean by typewritten, but the manuals selected were neither produced on typewriters (or printers), nor duplicated by photographic matters (that's why I selected early ones where that technology was still unavailable/too expensive). Those manuals have been typeseted the classic way using linotype style machinery. Also, excluding a common style of book typesetting style isn't exactly supporting the question.

@manassehkatz-Moving2Codidact Typesetting wasn't an inhouse issue back then especially not "your typical small publisher" . That's a rather recent development made possible by closed digital production cycles. Publisher delivered their material as typed pages with instructions to the print house which turned those pages into the book layout according to mandatory instruction sheets. It was those print houses that could afford typesetting the linotype way who also switched first to computer based using mainframes. As usual a business detail most people never see.

@MarkMorganLloyd Not really, above are printed manuals that have been typesetted. Of course there were as well read-me style manuals delivered on the same tape as the software, but those were not the same as above linked books (though there was a short phase before 1980 where IBM tried that - failed terribly). Of course, for the ones really operating the machines those printouts were usually the first (and last) documentation they got, so it' more present in our memory than the nice cut books management hoarded :)

@Raffzahn By typewritten I mean produced with printers that already output monospace fonts, such as daisy wheel printers, or are already formatted with monospace fonts. I'll edit the question to clarify.

@PaoloAmoroso This is exactly why I selected those old IBM manuals. They are all typesetted, not produced by some daisy wheel printers (which were not a thing in 1960) - in fact, IBM Selectric, which would have been IBM's device of choice, was quite able to produce proportional output. The pint selecting those manuals of the same time is to show that use of proportional or fixed are select on purpose, not due necessity o/ tools used. IBM, as others, had all at hand to go either way - and they did.

@Raffzahn: Neither any Selectric typewriter, nor any other IBM typewriter that could use the same type balls, could produce proportional type. The IBM Executive line of typewriters produced proportional-spaced text using type bars, and there was a type-ball-based typewriter that could do proportional spacing, but from what I read it was very expensive and rare, and its balls were incompatible with anything else.

@supercat The Selectric line is not the same as the Executive, which is an earlier different development. You may want to lookup the 1966 Selectric Composer. Likewise the MC Executive of197, which is, despite the name, a Selectric.

@Raffzahn: The Composer is the expensive and rare machine I was thinking of. I'd forgotten that it was called the "Selectric Composer", but it was from what I read its mechanical workings were almost nothing like the rest of the Selectric line. I know the Executive is different from the Selectric--my point was that IBM had a popular line of typewriters that could do proportional spacing, and an even more popular line of typewriters that used interchangeable balls, but no popular product line that combined those features.

@supercat The Composer is mechanically a mostly standard Selectric. Popularity is not a point here as it'snot about Joe Average typing a letter.

@Raffzahn: Even if the phrase "the Selectric" is interpreted as including obscure models that supported proportional spacing, I would not expect such a device to be used in leiu of a Linotype except when producing one-off documents or, perhaps, when cutting stencils or producing spirit masters. The "monospaced" example in another answer looks to my eye like it was produced via line printer, rather than a typewriter.

@supercat The Composer was in no way 'obscure' but quite successful. Just because it wasn't something everybody needs doesn't make it 'obscure'. Also it doesn't help if you twist what is said. The point is about that proportional typewriters were as available and in use, so the term 'typewriter' alone doesn't hold any value to exclude books.

Typesetting wasn't an inhouse issue back then especially not "your typical small publisher". - This must be an assumption, because it's not true. I worked as an apprentice printing machinist in the mid '80s for a very small publisher. We had an already ancient Linotype only the boss knew how to use, and a computerized film phototypesetter that I was almost as fascinated by but was never shown how to use. We were such a small publisher that I don't know what we published as we mostly did office stationery, wedding invitations, and the like. I doubt we were very atypical.

Oh I nearly forgot, a friend of mine even before my apprenticeship, 1980-82 era, had a dad who was an even smaller publisher working out of a home office. He used what I assume was a regular consumer level IBM Selectric golfball typewriter. We were allowed to use the TRS-80 Model 1 with Exidy Stringy Floppy, but we were forbidden from touching the Selectric. So I suppose it depends how small is "small". My print shop had 3 machinists, 2 in the art/typesetting department, 1 who only used the computerized film typesetter, and the boss and secretary/receptionist in the office.

@hippietrail Sure it was a publisher, not a printshop? But then there are as well way bigger publishers without - For example some of the largest pocket book publishers in Germany (dozend or more titles a month) didn't have in house printing. I would bet that even in your small company there was a workflow established with a clear distinction between publishing (lectoring / preparing a book) and typesetting. That is past wedding invention of course :) (Stringy Floppy ... neat!)

@Raffzahn I mostly only worked on the presses and the dark room making printing plates. I believe my boss took over the place from his father and that it had been there for quite a long time so maybe they did more publishing before I was there or maybe it was only ever very very small-time. I remember one thing we published and printed was a very small book, almost a pamphlet, on Aboriginal words. I found its ISBN: 0858080087. I don't think we ever did a new run while I was there but there were some copies or boxes around.