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dolffydos

wallneradam

Dolffy DOS is a drop-in KERNAL ROM replacement for the Commodore 64 that combines DolphinDOS parallel speed and a clean-room JiffyDOS serial fast loader, with optional Ultimate SoftwareIEC DMA and clock features.

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License

MIT

Last updated

2026-07-14

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FR-AI / ANALYSIS

Why it is worth attention

It reclaims ROM space from unused features (monitor, function-key macros) to maximize disk speed, automatically selects the fastest protocol per drive, and offers five builds tailored to different hardware and use cases.

Who it is for

  • Commodore 64 users wanting faster disk access
  • Retro gamers and demo scene enthusiasts
  • Owners of Ultimate 64, 1541 Ultimate-II+, or C64 Ultimate
  • C64 developers and hobbyists experimenting with fast loaders

Use cases

  • Loading games and tools in seconds instead of minutes
  • Mixing parallel, JiffyDOS, and stock drives on the same bus without reconfiguration
  • Using an Ultimate SoftwareIEC folder as a fast, writable C64 drive via DMA
  • Quickly loading and starting a program with the Quickrun build's one-key shortcut

Strengths

  • Combines three disk accelerators (DolphinDOS parallel, JiffyDOS serial, Ultimate DMA) in one 8 KB ROM
  • Per-device autodetection picks the fastest protocol without per-program setup
  • Clean-room JiffyDOS implementation avoids copyright issues and measures to match timing
  • Available in five distinct builds (Plain, Quickrun, Hyper, Hyper Quickrun, Ultimate) for different hardware and feature preferences

Considerations

  • Requires separately obtained drive ROMs (DolphinDOS 1541 ROM and licensed JiffyDOS drive ROM) to use the fast paths
  • Hyper DMA speed only works on Ultimate-family hardware with Command Interface enabled; VICE does not support it
  • Ultimate clock build has a wider compatibility surface and may conflict with cartridges using NMI or IO1/IO2
  • JiffyDOS serial fast path is a few seconds slower than original JiffyDOS in measured tests

README quick start

Installation

Description

Dolffy DOS (Dolphin + Jiffy) is a drop-in replacement for the C64 KERNAL ROM.

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