The Disappearing Foundations of Computing

In the 1960s-1990s, every hacker absorbed fundamental truths about ASCII bit structures, RS-232 voltage swings, and the clatter of teletypes through sheer osmosis. This knowledge wasn't academic—it was survival gear for interacting with the era's hardware. Today, as Eric S. Raymond meticulously documents, that cultural memory is evaporating. Understanding this lost world isn't just nostalgia; it's key to deciphering lingering quirks in modern systems, from Unix terminals to version control.

Terminals: From Teletypes to Glass TTYs

Before SSH and TCP/IP, users connected via VDTs (Video Display Terminals) or their ancestors: Teletypes. The iconic ASR-33 Teletype (1963) used a noisy electromechanical printer, consuming paper and echoing its operation in Unix's persistent /dev/tty device naming. Its legacy includes:
- Carriage Return (CR, \r): Physically moved the print head left. Unix later standardized on Line Feed ( ) alone, while Windows kept \r .
- 30ms Delays: Slow mechanical returns forced sending CR before LF to prevent characters "smearing" mid-line.

VDTs like the DEC VT-100 (1978) replaced teletypes, introducing:
- 24x80 Displays: Inherited from punch cards, defining default terminal sizes still used today.
- ANSI Escape Codes: Standardized cursor control (e.g., \x1b[2J to clear screens), now embedded in terminal emulators.
- The Meta Key: Asserted the 8th bit in 7-bit ASCII, enabling extended characters—a precursor to Alt keys.

RS-232: The Glue That Held Systems Together

Before Ethernet dominated, RS-232 (1962) connected terminals, modems, and peripherals. Its quirks were legendary:
- Baud Barf: Garbage output if mismatched settings (speed, parity, stop bits) weren't manually synchronized. 8N1 (8 bits, No parity, 1 stop bit) eventually dominated.
- Handshake Hell: DTR (Data Terminal Ready), DCD (Data Carrier Detect), and RTS/CTS signals negotiated connections. Cheap cables often omitted critical pins.
- Voltage Shocks: Traditional RS-232 used ±15V swings. Connecting TTL serial devices (0-5V) without a level shifter fried hardware.

Modems bridged RS-232 over phone lines. The Hayes Smartmodem (1981) revolutionized with its AT command set:
- ATDT5551234 dialed numbers. The AT prefix's bit pattern (1+0 1000 0010...) allowed auto-baud detection—a trick still used in 4G modems today.
- 56K Max Speed: Painfully slow vs. modern broadband, explaining why embedded devices (like GPS pucks) often default to 9600 baud.

ASCII: More Than Just Letters

ASCII (1963/1967) defined computing's textual DNA. Its control characters (0-31) had tangible purposes:

Char Mnemonic Original Use Modern Echo
\x00 NUL Tape filler C string terminator
\x07 BEL Teletype bell Terminal bell/flash
\x08 BS Backspace (non-destructive) Shell history search
\x0C FF Eject paper (Teletype) clear screen command
\x1B ESC Switch tape charset ANSI sequence initiator
\x7F DEL Rub out tape punches Delete key

Octal's Persistence: Early 36-bit machines (PDP-10) used octal for 3-bit fields. This bled into Unix via PDP-7/11 heritage, leading to C's (and later Python/Java's) \077 octal escapes—a syntax now largely obsolete but stubbornly persistent.

Networking Before the Internet

Pre-TCP/IP, hackers built global networks with ingenuity:
- UUCP (Unix-to-Unix Copy): Store-and-forward email/USENET over modems. Exploited flat-rate local calls via "bang paths" (bigsite!foovax!barbox!user). Key to early open-source collaboration.
- BBSes (1978-1996): Dial-up bulletin boards using protocols like XMODEM—whose packet structure (SOH, ACK, NAK) borrowed ASCII controls. Cisco routers still accept firmware via XMODEM today.
- The "September That Never Ended" (1993): When AOL granted USENET access to millions, overwhelming the existing culture—a cautionary tale for community scaling.

Why This Still Matters

  1. Legacy Systems: Industrial controllers, medical devices, and routers still use RS-232/serial. Debugging requires understanding handshake lines or voltage levels.
  2. Protocol Quirks: SMTP's 7-bit heritage led to MIME encoding. Terminal escape sequences (\x1b) live on in SSH tools.
  3. Cultural DNA: core dumps, SIGHUP (modem hangup), and Git's distributed model evolved from DECUS tapes and CVS.

As Raymond notes: "Tools generate culture." When RS-232 and teletypes vanished, a layer of shared understanding went with them. Recovering this context reveals why our systems behave in seemingly arcane ways—and honors the infrastructure that made modern computing possible.

Source: "Things Every Hacker Once Knew" by Eric S. Raymond