etex and pdftex have diverging memory constraints?

Hi,

Sorry if this is very basic, but I always thought the sole difference between etex and pdftex is that the former works to produce a dvi and the latter a pdf.

So, I was surprised to discover (or perhaps I observed that years ago and forgot) that pdftex has slightly more constrained memory constraints on macro expansion.

Here is a test file testxintLength.tex

----
\input xintkernel.sty
\edef\x{\romannumeral\xintreplicate{%     
2492679%
}{F}}
\expandafter\xintLength\expandafter{\x}
\bye
----

(the code creates a macro \x expanding to 2492679 F's then attempts to measure how many F's there are).

Compilation with etex succeeds  (even with 2492694 in place of 2492679).

$ etex testxintLength.tex
This is pdfTeX, Version 3.141592653-2.6-1.40.28 (TeX Live 2025) (preloaded format=etex)
 restricted \write18 enabled.
entering extended mode
(./testxintLength.tex (./xintkernel.sty) [1] )
Output written on testxintLength.dvi (1 page, 216 bytes).
Transcript written on testxintLength.log.

But compilation with pdftex fails.

$ pdftex testxintLength
This is pdfTeX, Version 3.141592653-2.6-1.40.28 (TeX Live 2025) (preloaded format=pdftex)
 restricted \write18 enabled.
entering extended mode
(./testxintLength.tex (./xintkernel.sty)
! TeX capacity exceeded, sorry [main memory size=5000000].
<inserted text> 2492679
                        \xintlength ...xint_c_i \xint_c_ \xint_bye \relax                                                     l.5 \expandafter\xintLength\expandafter{\x}
                                            !  ==> Fatal error occurred, no output PDF file produced!
Transcript written on testxintLength.log.

I am a bit surprised because I can not connect the constraints on TeX macro expansion with the output format DVI or PDF.  Needless to say I am completely ignorant of the innards.

If replying please CC as I am not on the list.

Kind regards

Jean-François