The more you go into the past, the better technical documentation you will find.<p>The documentation from the nineties of the 20th century was much better than the later documentation, and that from the seventies and the eighties was probably the peak, e.g. the various manuals of the Hewlett-Packard instruments, and also various manuals from DEC, IBM, Tektronix, National Semiconductor, Motorola, Intel, AMD, Texas Instruments, Fairchild and many others. Also many European companies had excellent technical documentation, e.g. Philips, Thomson, Siemens, SGS-ATES and many others. Many ancient manuals have been preserved at bitsavers.org and at a few other similar sites.<p>I believe that the FreeBSD manual from 1995 was better than any later operating system manual from the point of view of the completeness of its coverage of the existing features. The Gentoo manual before 2005 was also excellent. Both FreeBSD and Gentoo have good documentation even today, but nevertheless their manuals have not been kept completely up-to-date, so now they contain various holes about features that are not covered, unlike in the original complete manuals.<p>Before the Internet, for those who were not living in USA it could be very difficult to obtain many of the manuals and datasheets published by US companies, except perhaps at their booths at some international trade fairs.<p>After the Internet appeared, I was very happy that suddenly it became trivial to obtain any technical documentation, even if in the beginning that was done by FTP on dial-up modems at speeds as low as 2400 b/s.<p>Unfortunately, the time when it became easy to obtain technical documentation has coincided perfectly with the time when there was a tremendous decline in the quality of the technical documentation. Now it is easy to obtain technical documentation, but its content is much less valuable.<p>In many cases, e.g. for embedded processors and various complex interface integrated circuits, until you perform some tests on development boards you cannot be completely sure about how certain things work, instead of being able to predict any behavior based on the documentation. Moreover, if a company provides some example programs, they frequently contain valuable information that is missing from the manuals or datasheets.