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Knowledge Base›MIT CADR›Uses of the Super modifier on the MIT CADR and LM-3

Uses of the Super modifier on the MIT CADR and LM-3

Bottom line

Super was an independent character modifier, not a uniform “more Meta” level. In the audited CADR software its meaningful roles cluster into four groups:

  1. entering ZWEI numeric arguments without inserting a digit;
  2. choosing condition-specific Error Handler recovery actions;
  3. requesting an unusually strong ZMail composition abort; and
  4. controlling one direction of rotation in Spacewar.

Other subsystems preserve and compare the Super bit but intentionally normalize, ignore, or discard it. System selection strips it, ordinary TV menus generally do not assign it a distinct row action, and the selected network-terminal encoders do not transmit it. These negative paths are uses of the modifier in the dispatch sense and are included below.

Evidence boundary and notation

This article separates three profiles:

Profile Evidence Boundary
C46 Public MIT CADR System 46 source at Git commit 8e978d7d1704096a63edd4386a3b8326a2e584af Complete public snapshot, but the Zmacs overlay and some later applications are absent.
C303-SRC Maintained LM-3 source at Fossil check-in 4df393c68d7f083ce42d5c377039d26043cc18a9031ace28258dc97f4137eb91, tag system-303 Readable maintained source, not a pristine historical distribution tape.
C303-RUN Museum System 303 load band exercised through the CADR Xvfb harness Establishes only the explicitly recorded runtime observations.

C-, M-, S-, and H- mean Control, Meta, Super, and Hyper. Sh- means Shift. A chord containing Super is cataloged here even when other modifiers are also held. File and character-reader syntax varies between #/S-A, #\s-A, and long names such as Super-Abort; the normalized spelling here is Super-A.

The source audit searched character literals, character-bit operations, comtab constructors, System/Terminal dispatch, pointer modifier extraction, manuals, and the already completed application binding audits. Bug archives and superseded patch bodies were checked for leads but are not promoted to active release bindings without selected-source evidence.

Application summary

Application or substrate Super role Confidence
ZWEI and Zmacs Numeric-argument digits and minus in System 303 Complete selected-source table
Error Handler Dynamic Super-A through Super-Z recovery/special choices Source, manual, and runtime
ZMail composition Super-Abort invokes the stronger abort-send path Selected source
Spacewar Left Super turns the left ship right; Right Super turns the right ship right System 46 source and runtime dossier
System key and window selection Modifier is preserved in C46 exact dispatch but stripped in C303; it does not mean “new” Selected source
TV menus and chooser rows Modifier bit is represented, but ordinary row selection generally normalizes it away Selected source
Supdup and Telnet No independent wire encoding; modifier is consumed/collapsed Selected source
EINE and System 46 standard ZWEI No standard Super editing family established Negative source result

ZWEI and Zmacs

Numeric arguments

System 303 uses Super primarily as an argument-introducing modifier. Modified digits invoke Numbers; modified minus invokes Negate Numeric Arg.

Super-containing family Effect
S-0 through S-9 Enter a decimal numeric argument.
C-S-0 through C-S-9 Same numeric reader.
M-S-0 through M-S-9 Same numeric reader.
C-M-S-0 through C-M-S-9 Same numeric reader.
Every corresponding family also containing Hyper Same numeric reader; cataloged in both modifier articles because both bits are significant.
S--, C-S--, M-S--, C-M-S-- Establish a negative argument.
Corresponding Super+Hyper minus families Establish a negative argument.

Unmodified digits still self-insert. Thus Super has no special semantic command here: it changes digits and minus from text into command-loop argument syntax. The exact numeric state machine is in the ZWEI/Zmacs binding audit.

System 46's preserved standard table does not establish this Super argument family. EINE's older table has only plain, Control, Meta, and Control-Meta rows.

No general Super editing level

The fixed System 303 standard table contains no general family in which, for example, Super-F means motion by a unit larger than the Control/Meta units. Application modes may bind individual Super characters, but that is a local namespace rather than a standard editor grammar.

A ZWEI bug archive records an experimental three-command set: Super-/; End of Expression Line, Super-N Down Expression Line, and Super-P Up Expression Line. It is not in the selected canonical System 303 comtab and is therefore archival evidence, not part of this profile.

Error Handler

System 303 assigns the clearest system-level meaning to Super letters:

Super-A ... Super-Z
└─ select entry 0 ... 25 from the choices constructed for the current condition

The letters are positions, not fixed commands. The Error Handler combines current proceed types, nonlocal resume handlers, and special choices, prints the available Super letters, and dispatches the selected position. A static statement such as “Super-A means Abort” is false across conditions.

The museum's synthetic runtime condition produced:

Runtime chord Choice in that condition
Super-A Abort to top level
Super-B Restart the Initial Process
Super-C Reset and arrest the Initial Process

That observation proves dynamic dispatch in the tested band, not those three meanings for every condition. The source also installs Super-Shift-C as the :STORE-NEW-VALUE special choice when that recovery is offered.

See Error Handler and graphical debuggers for the complete table, condition construction, and reviewed runtime screenshot.

ZMail composition

The System 303 reply comtab distinguishes:

Chord Command Meaning
Abort or Control-] Abort Send Ordinary composition abort path
Super-Abort Really Abort Send Stronger, explicitly separate abort path

This is an application-local intensifier: Super selects the more forceful member of an abort pair. It does not establish a general rule that Super always means “really.” The complete reply and message-editor inheritance is in ZMail keybindings.

Spacewar

Spacewar reads the physical modifier-key switch bits as game controls rather than as character prefixes:

Player Physical key Effect
Left ship FOO Left Super Turn right
Right ship BAR Right Super Turn right

Hyper turns in the opposite direction, Shift enters hyperspace, Meta fires, and Control accelerates. While the instruction display is still visible, pressing any Control, Meta, Super, or Hyper key starts play. The complete control/physics audit is Spacewar on the MIT Lisp Machine.

System selection and window management

Super participates differently in the two source profiles:

Profile Super-bearing System suffix
C46 Modifier bits are preserved. Only an exact modifier-bearing registration can match; an ordinary base registration is not automatically selected.
C303-SRC System records whether Control was present, then strips all modifier bits. Super therefore resolves to the base registered suffix. Only Control changes the branch by requesting valid flavor creation.

Consequently, Super-System-L is not a higher-level Listener command in System 303. It normalizes to System-L; Control-System-L is the meaningful “force a new instance” variation. The Terminal prefix, by contrast, preserves exact modifier bits for any explicitly registered suffix.

See the program-selection specification.

TV menus, mouse rows, and generic pointer dispatch

System 303 pointer characters have five modifier bits: Shift, Control, Meta, Super, and Hyper. A three-button menu can therefore be tested under 32 modifier states per button. The modifier is real and survives input encoding, but ordinary momentary menu rows select by normalized primary button and do not give Super a distinct row meaning.

This matters for compatibility: a clone must preserve the bit and pass it to application code, while a generic chooser must not invent a Super alternate action. Applications such as Inspector can separately inspect held modifier state; that specific use belongs to the Hyper catalog.

Supdup, Telnet, and character transmission

The selected CADR terminal filters encode Control and Meta but do not allocate independent Super or Hyper wire bits. A Super-bearing input either reaches the same translation indexed by its base/remaining encoded state or is consumed according to the active table; it is never sent as a portable “Super” modifier.

“Super-image” mode in the NVT sources is unrelated to the Super key. It names a raw keyboard/input-buffer mode and must not be counted as a modifier use. See Supdup and Telnet bindings and protocol semantics.

Negative and nonbinding results

  • No standard EINE Super row is present in the audited late-1977 table.
  • The complete public System 46 standard ZWEI table establishes no general Super argument or editing family.
  • System 303 generated lowercase/Hyper aliases do not create Super aliases.
  • Generic menu enumeration covers Super states, but coverage is not a distinct action.
  • :SUPER-IMAGE, “superior” windows, superpackages, and file supersession are lexical false positives, not keyboard uses.
  • The source reader accepts names such as Hyper-Super-A; accepting a character name does not bind it.

Interpretation

Across the established CADR uses, Super is best understood as spare semantic capacity rather than a consistent editing scale. The Error Handler uses it as a dynamic choice bank, ZMail as an intensifier, Spacewar as a physical game switch, and ZWEI as an argument marker. Software that merely preserves or strips the bit must remain distinguishable from software that assigns it an action.

Sources and verification

Last verified: 2026-07-26.

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