DOS ain't dead

Was: Ctrl-Z was never actually an EOF character in MS-DOS (Miscellaneous)

posted by tkchia , 11.02.2026, 16:43
(edited by tkchia on 11.02.2026, 17:07)

Hello bencollver,

It turns out that Michal Necasek had written a reply to precisely this article, where he basically said, "well actually"...

https://www.os2museum.com/wp/misconceptions-on-top-of-misconceptions/

> What CP/M versions 1.x/2.x as well as 86-DOS 0.x had in common is that file sizes were not stored with byte granularity. Instead, file sizes were only tracked in terms of 128-byte "records", which typically happened to correspond to 128-byte floppy disk sectors.
>
> ... for text files, or possibly other data files, this was a problem. No one wanted up to 127 bytes of junk displayed on the screen or sent to the printer. CP/M, like old DEC operating systems, adopted the ASCII SUB (substitute) character in order to solve the problem.

So Ctrl-Z in text files was really a weird holdover from the days of MS-DOS 1.x FCBs. (Incidentally, DOS 1.x lossage also explains why uncompressed .exe files tend to have their MZ headers padded up to a multiple of 512 bytes, even though MZ headers lengths are given as 16-byte paragraphs...)

Thank you!

---
https://codeberg.org/tkchia · https://disroot.org/tkchia · 😴 "MOV AX,0D500H+CMOS_REG_D+NMI"

Complete thread:

• Ctrl-Z was never actually an EOF character in MS-DOS - bencollver, 11.02.2026, 16:18 (Miscellaneous)
  • Was: Ctrl-Z was never actually an EOF character in MS-DOS - tkchia, 11.02.2026, 16:43
    • Was: Ctrl-Z was never actually an EOF character in MS-DOS - bencollver, 11.02.2026, 19:26
  • Ctrl-Z was never actually an EOF character in MS-DOS - bretjohn, 12.02.2026, 02:45
    • Ctrl-Z was never actually an EOF character in MS-DOS - bencollver, 12.02.2026, 15:40
      • Ctrl-Z was never actually an EOF character in MS-DOS - bretjohn, 14.02.2026, 02:34