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pushing the Wombat Macs way too far (Centris 650, Quadra 650, Quadra 800)

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This is a repository for information and code to push the capabilities of the codename "Wombat" machines (the Centris 650, Quadra 650, and Quadra 800) as far as possible.


Main project goals:

  • stable and functional overclock beyond 40 MHz
  • detecting and configuring 64MB and 128MB RAM SIMMs

Current status:

  • Overclock to 50MHz (but without functional serial and network, and eventual video glitches)
  • Maximum RAM up to 8MB + 3x 128MB, with some limits and issues

To squeeze everything out of these machines, you will need to:

  • change the configuration resistors on the back of the mobo
  • swap in a nicer 68040 chip, the later the better
  • apply a faster clock (solder on a faster oscillator or get a MacClip)
  • solder in a ROM socket (part number 650473-5)
  • get a programmable ROM and burn one of my (cy384's) modified ROM images to it
  • probably add a better heatsink, maybe with a fan, to the CPU

terminology and machines

Apple used a lot of internal codenames, a few relevant ones here:

  • Wombat: the motherboard used in the C650, Q650, and Q800
  • djMEMC: the memory controller used on the Wombat macs
  • speedbump: after the release of the C650, Q650, and the Q800, faster ("speedbump") versions were under development, up to 40MHz, but mostly not released
  • plastics or package: case model
  • Frigidaire or fridge: the Q800 case
  • Lego: C650 and Q650 case
  • WLCD: C610 and Q610 case

From "Universal.a", some of the supported machines by the final 68k ROM (post-dating the ROM versions that shipped with any Wombats) are:

  • "33MHz Frigidaire package (Quadra 800)" gestalt ID 35
  • "40MHz Frigidaire package (unreleased)" gestalt ID 59?
  • "20MHz WLCD (Centris 610)" gestalt ID 52
  • "25MHz WLCD (Quadra 610)" gestalt ID 53
  • "33MHz WLCD (unreleased)" gestalt ID 63?
  • "25MHz Lego package (Centris 650)" gestalt ID 30
  • "33MHz Lego package (Quadra 650)" gestalt ID 36
  • "40MHz Lego package (Quadra 650 SpeedBump, unreleased)" gestalt ID 51?

Based on jumper and resistor placement, a Wombat can report being a 30, 35, 36, 51, or 59. Note that early versions of Mac OS 7 don't support all of these! I believe 7.5.3 does.


Pictures describing how I added a socket to my Wombat board, for easy oscillator swapping. Takes standard 'full size' DIP14 5V oscillators.


This is a simple program that reads and pretty-prints data from the djmemc memory controller registers. Useful for figuring out how the ROM is configuring the machine.


A tiny, lazy pile of hacks to modify and build a Wombat ROM. There are a few partially disassembled ROMs, with changes to allow overclocking and RAM increases.

external docs

Reference copies of various useful documents and notes.

stock roms

Reference copies of the two Wombat ROMs I'm aware of: checksum F1A6F343 (Centris 650?) and F1ACAD13 (Quadra 650, Quadra 800?). Supposedly these were also used for the Centris/Quadra 610 machines.


pushing the Wombat Macs way too far (Centris 650, Quadra 650, Quadra 800)






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