The second link is exactly what I was hoping for, but only seems to exist on the archive. I wasn't able to locate it or other detailed information with my cursory searches. I'm glad it was preserved.
It’s basically just configuration data for MS-DOS apps running under Windows (or some over MS-DOS multitaskers). Stuff like EMS and XMS memory amounts, various config options etc.
Fun fact: under the hood, PIF files are sent to the same ShellExecute function as EXEs, and if you have an EXE with a PIF extension, it runs the EXE code as normal.
Funnier fact: In Windows 95 and onwards, the UI presents PIFs as a special case of shortcuts, and as with LNK files, Windows always hides (hid?) the extension, even if you have “always show extensions” on. When I get home, I’ll have to check if Windows 11 still has this behaviour…
Edit: Yeah, creating a copy of calc.exe in my ~/Documents folder and renaming it calc.docx.pif does result in a working calculator file that presents gives its name as "calc.docx", albeit with a "shortcut to generic file" icon and a type of "Shortcut to MS-DOS Program" despite the fact that I can't think of any legitimate reason to do anything with a real PIF file on Windows 11 (24H2).
I just checked on a Win11 VM, with show extensions and show hidden turned on, I created a test.pif file on the desktop and the extension is NOT visible. It appears as a shortcut with the little arrow on the icon, and the properties list the file type as "Shortcut to MS-DOS Program (.pif)".
Back in the day, sending the string ".pif" to any MSN Messenger group chat was enough to immediately disable it for everyone. Fun way of dealing with spam :)
Googling a bit, it looks like a lot of this lore has just been lost. I don't know if there are modern explanations of PIF files kicking around.
⁂ I realize this is an ATM machine phrasing, but we called them PIF files in the day.