This is said in TeXbook about page dimensions:
Plain TEX sets \vsize=8.9in (not 9in, since \vsize doesn't include the space for page numbers at the bottom of each page)...
According to definition of \makefootline, the space occupied by it is 24pt. According to definition of TeX's pt we get 24/72.27 = 0.3in
According to TeXbook space occupied by footline is 0.1in, but it is 0.3in. This implies that bottom margin must be 0.8in, not 1in (how to trace that?).
Besides, it is strange that \nopagenumbers
leaves 24pt at the bottom of page, because if we don't want page numbers, why do we want extra space? (e.g., headline does not contain anything by default - and it does not hold any extra space) Wouldn't the definition of \nopagenumbers
be more reasonable if it was \gdef\makefootline{}
? (in this case also \vsize
must also probably be increased by 24pt)
These are definitions of \makefootline
and \nopagenumbers
from plain.tex, to make the question self-consistent:
\def\makefootline{\baselineskip24\p@\lineskiplimit\z@\line{\the\footline}}
\def\nopagenumbers{\footline{\hfil}} % blank out the footline
The following topics provide additional info:
How to draw borders around page contents
How is a page produced in the output routine?