It's a DE9, not a DB9 (but we know what you mean)

Original Article ↗ Hacker News Discussion ↗

Serial ports, RS-232, and connector variety

  • Many commenters just call it a “serial port” and can’t remember the exact D‑sub code; others point out even that’s ambiguous (RS‑232 vs RS‑422/485, SIO, USB, etc.).
  • Discussion of why DB‑25 existed for serial despite only needing 3 wires in simple cases: hardware flow control, modem control signals, differential pairs, synchronous clocks, and even powering devices.
  • DE‑9 vs DB‑25 pin usage: most practical serial links used few signals, often only 3; soft (XON/XOFF) flow control eventually displaced hardware handshaking for many uses.
  • Real-world serial implementations: Cisco-style RJ45 console ports, Yost pinouts, proprietary RJ-style serial, terminal blocks, MMJ on DEC gear, and odd “octopus” fan-out cables.

D‑sub nomenclature and odd variants

  • The article’s point: a 9‑pin D‑sub in the small shell is technically DE‑9, not DB‑9; letters A–E refer to shell size, number is pin count.
  • Commenters note many counterexamples:
    • DE‑15 (VGA), DA‑15 (Mac video, joysticks, AUI Ethernet).
    • High‑/double‑density parts (e.g., DE‑15 vs DE‑9 in same shell; DB‑25 vs DB‑44).
    • Mixed-contact versions with high‑current pins, coax (DB13W3), fiber, even pneumatics.
    • Nonstandard 19‑ and 23‑pin shells (Amiga, DB‑19), partial-populated DB‑25s, “DE‑0” shells with no contacts.
  • Some argue the shell letter is hard to interpret and a row/pin‑based code (e.g., D2‑15 vs D3‑15) would have been clearer.

RJ45, 8P8C, and genericized connector names

  • Several comments stress that “RJ45” is formally a keyed, telephone‑oriented registered jack with a programming resistor and incompatible wiring; Ethernet uses an unkeyed 8P8C “modular jack.”
  • In practice, industry and contracts routinely say “RJ45” to mean Ethernet 8P8C, and trying to enforce the old strict definition is seen as counterproductive.
  • Similar genericization examples:
    • “Molex” for various 4‑pin power connectors;
    • “JST”, “DuPont”, “Berg” for families of 0.1" board-to-wire parts;
    • Military/aviation multi‑sourced connectors (e.g., 38999, LEMO‑style).

Pedantry vs practical communication

  • One camp: words must be precise in engineering—mislabeling DB‑15/DE‑15 or RJ45 can cause wrong parts, rework, or contract disputes. Precision is crucial in drawings, purchasing, safety, and high‑impact operations.
  • Other camp: DB‑9 and RJ45 are de facto names; insisting on DE‑9 or 8P8C in everyday conversation is seen as “well actually” pedantry that adds little clarity. Many would still search or order under the colloquial terms.
  • Several note that in linguistics, meaning follows usage: “decimate”, “literally”, “reign/rein”, “double precision”, “kettle lead” all illustrate drift from original technical meanings.

Connector longevity and broader trivia

  • D‑subs date to the 1950s and are still used in aerospace, space hardware, and industrial gear; they now carry high‑current, coax, fiber, even fluids.
  • Other long‑lived standards mentioned: 1/4" and 3.5mm phone jacks (19th century origins), DIN, XLR, RCA, Belling‑Lee antenna connectors, Edison screw lamp bases, MIL‑DTL‑5015, and cigarette‑lighter power sockets.
  • Numerous side threads touch on floppy disk “1.44 MB” units vs MiB, hard‑drive vs OS capacity units, ISPs advertising gigabits, misuse of PST vs PDT, and recurring “Frankenstein’s monster” corrections as parallels to DB‑9 pedantry.