Questions regarding Apple “Houdini I” DOS Compatibility Card from Quadra 610 (with 486 SX 25 CPU)

[MrFahrenheit]

I apologize if these questions have already been asked elsewhere in the forum. I searched and could not find anything relating to this.

I have an Apple Houdini I DOS Compatibility Card that came inside a Quadra 610 DOS Compatible machine I bought in 2020.



I would like to upgrade the CPU on this card to something faster than the SX/25 that it includes.

I have this CPU which I recently purchased new in box:




This CPU (DX2ODPR) is meant for 486 33mhz systems. Will it work fine, but at 2x25 (for 2/50 effective)? Or will it fail to work? Could something be damaged by trying this CPU in the Houdini Card?

Another question, will the original Houdini card work with a DX CPU? The Houdini II cards have a jumper to switch SX and DX. This card lacks any jumpers at all.

Lastly, has anyone got adapter boards available that I can trade or purchase that would allow this card to work inside a Q650/800? I’d much rather use it inside my 650.

 

[dougg3]

I also have one of the Houdini I cards and have been playing with it recently, but haven't gotten the courage to think about upgrading its CPU yet. However, I did do some initial research about it. It turns out that back in the '90s there was a FAQ with all kinds of tidbits about the card, but all traces of it have since disappeared from the internet. Luckily the Internet Archive saved it all. I think this FAQ will be super useful for you:

• https://web.archive.org/web/19961226225303/http://www.paranoia.com/~anton/houdini/index.html
• https://web.archive.org/web/1997042...ranoia.com/~anton/houdini/houdini_faq_103.txt

To be honest I'm still pretty green when it comes to understanding the Intel CPUs, but it sounds like there are some small modifications you can make to the board (removing a 0-ohm resistor and adding a few in other places) to configure it for a DX. Straight from the horse's mouth (from someone with an @apple.com email address):

The pinouts of the SX, DX, and DX2 are different. However, it is
possible to upgrade. An enterprising person with the pinouts of the
various 486's and an ohmmeter can find the hooks we put on the board to
make the swap.

In the FAQ it sounds like they've traced it out to removing R56 and populating R54, R55, and R57. It also recommends to add a fan if you install a DX2/DX4. It's also mentioned that it'll run at 50 MHz even if you install a DX2/66.

One other thing that was brought up is the board components are good for 33 MHz if you want to try clock chipping, but some of the BIOS routines are timed for 25 MHz so YMMV. Sadly there are no mentions of success or failure in the FAQ.

By the way, this FAQ has all kinds of other interesting tidbits, with lots of useful info from an Apple employee. For example it mentions an easter egg in the PC Setup control panel that gives you a fake DOS prompt that also lets you do things like enable/disable the 610's Mac side sync-on-green. It even gives us info on the pinout of the auxiliary connector, which is an incomplete ISA bus. Someone tried wiring up a Sound Blaster and it almost worked, except there were major issues with DMA. Guess that's one of the things they fixed on the Houdini II...

 

[Byrd]

Thanks for posting up those web archives, dougg3 - I've not seen them before. Wonder if there exists a 40Mhz bus speed mod for Houdini boards?

The pin sockets in these cards are tight (there have been a few posts where the unused boards did not work due to the CPU not being properly pushed in with the supplied CPU running red hot = I'm one of those people!), take care removing the CPU even consider spraying a small amount of WD40 around the pins for easier removal. Clean the socket well with electronic solvent spray before putting the Overdrive CPU in.

Have found DOS, Win 3.1, Win95 work very well but Win98 performed much slower than an equivalent 486 should run.

 

[GRudolf94]

An ODPR is just an SL-enhanced DX/2 set to ignore its CLKMUL pins - it's always internally strapped at 2x. An ODP is a 487-pattern chip and not relevant here.

Pinouts really do change between SX and DX - pin C14 is NC on the SX, becomes FERR# on the DX, pin A15 is NMI on the SX, becomes IGNNE# on DX, NMI moves to B15 on DX, formerly NC on SX. All other differences are related to the SX's omission of a JTAG test port, or the addition of the SL-enhanced SMI/STPCLK pins, and not relevant here. As one can imagine, FERR# and IGNNE# are related to FPU exception handling.

In short: NMI moves from A15 to B15, IGNNE wired to A15, FERR goes to C14.

 

[MrFahrenheit]

Thank you @dougg3 for the links. Very helpful!

 

[dougg3]

Have found DOS, Win 3.1, Win95 work very well but Win98 performed much slower than an equivalent 486 should run.

Thanks for the advice on cleaning and care with changing the CPU! My experience mirrors yours. Windows 98 was able to install on the stock SX CPU if I bypassed the FPU check with a flag to setup, but it’s super duper slow. 95 seemed all right.

Thank you @dougg3 for the links. Very helpful!

Glad to help! If you end up trying out a new CPU, I’m super interested in hearing how it goes.

 

[dougg3]

Pinouts really do change between SX and DX - pin C14 is NC on the SX, becomes FERR# on the DX, pin A15 is NMI on the SX, becomes IGNNE# on DX, NMI moves to B15 on DX, formerly NC on SX. All other differences are related to the SX's omission of a JTAG test port, or the addition of the SL-enhanced SMI/STPCLK pins, and not relevant here. As one can imagine, FERR# and IGNNE# are related to FPU exception handling.

In short: NMI moves from A15 to B15, IGNNE wired to A15, FERR goes to C14.

Thanks for providing the pinout differences! I decided to verify the resistors mentioned in the FAQ.

• R56 and R55 both have one end going to pin A15.
  • R56 is populated, so R56 must be for hooking NMI to pin A15.
  • R55 is not populated. Must be for hooking IGNNE to pin A15.
• R54 has one end going to pin C14.
  • Not populated. Must be for hooking FERR to pin C14.
• R57 has one end going to pin B15.
  • Not populated. Must be for hooking NMI to pin B15.

So...the info from the FAQ all lines up perfectly with the info you gave. Nice!