Infinite Mac Emulator Cores: Types, CPUs, and Capabilities

Infinite Mac runs seven distinct emulator cores in the browser as WebAssembly modules. Each core is compiled from the original C or Rust emulator source and wrapped in a common JavaScript interface. The right emulator is selected automatically based on the machine definition — you never configure this directly. Understanding which core is in use helps explain the differences in available features, mouse handling, networking support, and speed controls across different Mac and NeXT configurations.

The `EmulatorType` Union

export type EmulatorType =
    | "BasiliskII"
    | "SheepShaver"
    | "Mini vMac"
    | "DingusPPC"
    | "Previous"
    | "PearPC"
    | "Snow";

The `EmulatorCpu` Type

export type EmulatorCpu =
    | "68000"
    | "68020"
    | "68030"
    | "68040"
    | "601"
    | "603"
    | "604"
    | "G3";

The 68K values correspond to Motorola 68000-family CPUs used in all Macs from 1984 to the early 1990s. The 601, 603, 604, and G3 values represent IBM/Motorola PowerPC processors used in Power Macintosh computers from 1994 onward. Note that the 603 CPU type is defined but not currently assigned to any machine definition.

Capability Summary

Emulator	CPU	AppleTalk	Abs. Mouse	Opt. Rel. Mouse	Debug Log	BlueSCSI	Speed Config
Mini vMac	68000–68030	✗	✓	✗	✗	✗	`MACEMU`
Basilisk II	68030–68040	✓	✓	✓	✗	✗	`MACEMU`
SheepShaver	601, 604, G3	✓	✓	✓	✗	✗	—
DingusPPC	601, G3	✗	✗ (always rel.)	—	✓	✓	—
Previous	68030–68040	✗	✗ (always rel.)	—	✓	✗	—
PearPC	G3	✗	✗ (always rel.)	—	✓	✗	—
Snow	68000–68030	✗	✓	✓ (restart req.)	✗	✗	`SNOW`

Mini vMac

Mini vMac is the original emulator used for the earliest Macintosh hardware. It emulates compact 68K Macs from the original 128K through the Mac IIx, running System 1.0 through System 6.x (and some early System 7 configurations). Machines using this emulator: Mac 128K, Mac 512Ke, Mac Plus, Mac SE, Mac II, Mac IIx Emulator subtypes (EmulatorMinivMacSubtypes):

export type EmulatorMinivMacSubtypes =
    | "128K"
    | "512Ke"
    | "Plus"
    | "SE"
    | "II"
    | "IIx";

Each subtype compiles a different Mini vMac variant optimized for that specific hardware model.

Capabilities

Mouse mode: Absolute coordinates only. Mini vMac does not support relative mouse deltas (emulatorSupportsMouseDeltas returns false).
Interrupt key: Mini vMac is the only emulator that uses the programmer’s interrupt key (emulatorUsesInterruptKey returns true). This maps to a keyboard shortcut that triggers the 68K interrupt, useful for debugging or breaking out of hangs.
AppleTalk: Not supported.
Placeholder disks: Not used.
Debug log: Not supported.
BlueSCSI: Not available.
Speed control: Uses the MACEMU speed config — speeds from Default through 1x, 2x, 4x, 8x, 16x, 32x, and All Out.

Basilisk II

Basilisk II emulates 68K Macs with color displays, covering the Mac IIfx through the Quadra series. It supports System 7.x through Mac OS 8.1 and is the only 68K emulator with AppleTalk networking support. Machines using this emulator: Mac IIfx, Quadra 650

Capabilities

Mouse mode: Absolute coordinates by default. Optionally supports relative mouse deltas (emulatorSupportsMouseDeltas returns true). Switching does not require a restart.
AppleTalk: Supported (emulatorSupportsAppleTalk returns true). Basilisk II and SheepShaver are the only emulators with AppleTalk.
Placeholder disks: Uses placeholder disk files (emulatorUsesPlaceholderDisks returns true). The emulator requires disk “slots” to be pre-populated in its preferences even if no real disk is attached.
Debug log: Not supported.
BlueSCSI: Not available.
Speed control: Uses the MACEMU speed config (same as Mini vMac). A speedGovernorTargetIPS can be set on a machine definition to throttle overall throughput for realistic benchmark scores.
CPU ID mapping: Basilisk II uses an internal CPU ID: 68020 → 2, 68030 → 3, 68040 → 4.

SheepShaver

SheepShaver emulates PowerPC Macs using NewWorld ROM images. It runs Mac OS 8.x through Mac OS 9.0.4, the last release it supports. Like Basilisk II, it provides AppleTalk networking. Machines using this emulator: Power Macintosh 9500 (604), Power Macintosh G3 Blue & White (G3)

Capabilities

Mouse mode: Absolute coordinates by default; optionally supports relative mouse deltas (emulatorSupportsMouseDeltas returns true) without requiring a restart.
AppleTalk: Supported (emulatorSupportsAppleTalk returns true).
Placeholder disks: Uses placeholder disk files (emulatorUsesPlaceholderDisks returns true), same behavior as Basilisk II.
Debug log: Not supported.
BlueSCSI: Not available.
Speed control: None (emulatorSpeedConfig returns undefined).

DingusPPC

DingusPPC emulates PowerPC Macs with OldWorld ROM (NuBus and PCI machines). It supports System 7.5.2 through Mac OS 9.1, and is also used for early Mac OS X installations up to 10.1. Machines using this emulator: Power Macintosh 6100, 7200, 7500, G3 Beige, iMac G3 233, Power Macintosh G3 Blue & White (Experimental)

Capabilities

Mouse mode: Always uses relative mouse deltas (emulatorNeedsMouseDeltas returns true). Absolute coordinates are not supported; relative mode is automatically engaged for all DingusPPC sessions.
AppleTalk: Not supported.
Placeholder disks: Not used.
Debug log: Supported (emulatorSupportsDebugLog returns true). When debug logging is requested, the verboseBootEnvVars on the machine definition are applied to OpenFirmware to enable verbose boot output.
BlueSCSI: Optionally supported (emulatorHasOptionalBlueSCSI returns true). DingusPPC is the only emulator with BlueSCSI support.
Speed control: None (emulatorSpeedConfig returns undefined).

DingusPPC uses named monitorId strings in supportedScreenSizes (e.g. "Multiscan17in", "MacRGB15in") to tell the emulator which virtual monitor to emulate at each resolution.

Previous emulates the NeXT hardware family — the NeXT Computer (68030), NeXTcube (68040), NeXTstation (68040), and NeXTstation Turbo Color (68040). It runs NeXTSTEP 0.8 through NeXTSTEP/OPENSTEP 4.2. Machines using this emulator: NeXT Computer, NeXTcube, NeXTstation, NeXTstation Turbo Color Emulator subtypes (EmulatorPreviousSubtypes):

export type EmulatorPreviousSubtypes =
    | "NeXT Computer"
    | "NeXTcube"
    | "NeXTstation"
    | "NeXTstation Turbo Color";

Capabilities

Mouse mode: Always uses relative mouse deltas (emulatorNeedsMouseDeltas returns true).
AppleTalk: Not supported.
Placeholder disks: Previous expects all configured disk “files” to exist on the filesystem. Empty stub files are created for any unmounted slots (emulatorNeedsDiskPlaceholderFiles returns true).
Debug log: Supported (emulatorSupportsDebugLog returns true).
BlueSCSI: Not available.
Speed control: None (emulatorSpeedConfig returns undefined).

PearPC

PearPC emulates a G3/G4-class PowerPC machine for running early Mac OS X (10.0 Public Beta through 10.4 Tiger). It is the primary emulator for the Mac OS X disk collection. Machines using this emulator: Power Macintosh G4 (PCI Graphics)

Capabilities

Mouse mode: Always uses relative mouse deltas (emulatorNeedsMouseDeltas returns true).
AppleTalk: Not supported.
Placeholder disks: Not used.
Debug log: Supported (emulatorSupportsDebugLog returns true).
BlueSCSI: Not available.
Speed control: None (emulatorSpeedConfig returns undefined).

Snow

Snow is a Rust-based 68K Macintosh emulator developed specifically for Infinite Mac. It is the newest addition to the emulator lineup and aims to provide more accurate hardware emulation than Mini vMac for the same range of machines. Snow covers the Mac 128K through the Mac SE/30.

Snow is the only emulator in Infinite Mac written in Rust rather than C. It is under active development and progressively gains support for additional Mac models and hardware features.

Machines using this emulator: Mac 128K (Snow), Mac 512K (Snow), Mac 512Ke (Snow), Mac Plus (Snow), Mac SE (Snow), Mac SE FDHD (Snow), Mac Classic (Snow), Mac II (Snow), Mac II FDHD (Snow), Mac IIx (Snow), Mac IIcx (Snow), Mac SE/30 (Snow)

Capabilities

Mouse mode: Absolute coordinates by default, with optional relative mode. Unlike Basilisk II and SheepShaver, switching to relative mouse mode requires a restart (emulatorNeedsRestartForMouseDeltas returns true).
AppleTalk: Not supported.
Placeholder disks: Not used.
Debug log: Not supported.
BlueSCSI: Not available.
Speed control: Uses its own SNOW speed config with different semantics from the MACEMU config:

const SNOW_SPEED_CONFIG: EmulatorSpeedConfig = {
    defaultSpeed: -2,
    speedOptions: new Map<EmulatorSpeed, string>([
        [-2, "Accurate"],
        [7,  "Dynamic"],
        [-1, "Uncapped"],
        [9,  "Video"],
    ]),
};

The Snow speed values are kept in sync with the speed-handling code in snow/frontend_im/src/input.rs.

Speed Configuration Details

Two speed configuration presets are used across the emulators:

MACEMU (Mini vMac, Basilisk II)
Snow

const MACEMU_SPEED_CONFIG: EmulatorSpeedConfig = {
    defaultSpeed: -2,
    speedOptions: new Map<EmulatorSpeed, string>([
        [-2, "Default"],
        [0,  "1x"],
        [1,  "2x"],
        [2,  "4x"],
        [3,  "8x"],
        [4,  "16x"],
        [5,  "32x"],
        [-1, "All Out"],
    ]),
};

-2 means the default speed the emulator was compiled with. -1 (“All Out”) removes all speed limiting and runs as fast as the host CPU allows.

const SNOW_SPEED_CONFIG: EmulatorSpeedConfig = {
    defaultSpeed: -2,
    speedOptions: new Map<EmulatorSpeed, string>([
        [-2, "Accurate"],
        [7,  "Dynamic"],
        [-1, "Uncapped"],
        [9,  "Video"],
    ]),
};

"Accurate" targets original hardware timing. "Dynamic" adjusts speed based on load. "Uncapped" removes all throttling. "Video" is optimized for smooth video playback.

DingusPPC, Previous, and PearPC return undefined from emulatorSpeedConfig — they expose no speed controls to the user.

The `EmulatorDef` Discriminated Union

The EmulatorDef type enforces that Mini vMac and Previous subtypes are always specified:

export type EmulatorDef =
    | {
          emulatorType: Exclude<EmulatorType, "Mini vMac" | "Previous">;
          emulatorSubtype?: never;
      }
    | {
          emulatorType: "Mini vMac";
          emulatorSubtype: EmulatorMinivMacSubtypes;
      }
    | {
          emulatorType: "Previous";
          emulatorSubtype: EmulatorPreviousSubtypes;
      };

Any machine definition using emulatorType: "Mini vMac" must include a valid emulatorSubtype from EmulatorMinivMacSubtypes, and similarly for Previous. All other emulator types must not have a subtype.

Machines & Disks

Embed API

Infinite Mac Emulator Cores: Types, CPUs, and Capabilities

The `EmulatorType` Union

The `EmulatorCpu` Type

Capability Summary

Mini vMac

Capabilities

Basilisk II

Capabilities

SheepShaver

Capabilities

DingusPPC

Capabilities

Previous

Capabilities

PearPC

Capabilities

Snow

Capabilities

Speed Configuration Details

The `EmulatorDef` Discriminated Union

Build docs developers (and LLMs) love

Machines & Disks

Embed API

Documentation Index

​The EmulatorType Union

​The EmulatorCpu Type

​Capability Summary

​Mini vMac

​Capabilities

​Basilisk II

​Capabilities

​SheepShaver

​Capabilities

​DingusPPC

​Capabilities

​Previous

​Capabilities

​PearPC

​Capabilities

​Snow

​Capabilities

​Speed Configuration Details

​The EmulatorDef Discriminated Union

Build docs developers (and LLMs) love

The `EmulatorType` Union

The `EmulatorCpu` Type

Capability Summary

Mini vMac

Capabilities

Basilisk II

Capabilities

SheepShaver

Capabilities

DingusPPC

Capabilities

Previous

Capabilities

PearPC

Capabilities

Snow

Capabilities

Speed Configuration Details

The `EmulatorDef` Discriminated Union