Hello everyone,

I've been tinkering more and more with 386-based systems lately, and have run across something that I'm a bit perplexed about. From my understanding, the 386DX is fully 32-bit, and that the 386SX is a hybrid 16/32-bit setup, with an external 16-bit data path.

That being said, I've lately amassed a small number of co-processors for testing. I've got the following:

ULSI DX/DLC-40 in CPGA68
IIT 4C87DLC-40 in PGA68 on a factory PLCC-PGA converter
IIT 3c87-40 in the same package as its sibling
Cyrix Fasmath Cx83D87-40 on a factory QFP-PGA converter
Green Math 4C87DX-40 in a PLCC-PGA converter
Intel i387SX 16-25 PLCC
ULSI Math Co SX-33 in PLCC (currently in use)

A photo is attached for reference.

Here's the thing: I've got two 386 motherboards, and one on the way, and I wanted to run by some others with more experience a few questions as to the compatibility of these FPUs with CPUs.

First, I have an Alaris Cougar LX, with an IBM 486SLC2/50. From what I understand, functionally this chip is pretty much an i386SX in terms of it being both pin-compatible and sharing the i386SX's 16/32-bit hybrid bus setup. Does that then mean, then, that the only compatible FPUs would be the i387SX and ULSI Math Co (the Math Co is what's currently installed)? Or is it possible to use a DX-class FPU for an SX-based machine? I'd be interested in such a configuration in order to test out the Green Math coprocessor with this system, if capable.

I've also included a photo of the relevant motherboard. (Also, just a random digression, but I removed the Varta barrel battery. I've never before had a board with such a battery--at least not in recent years--and holy cow are they AWFUL. I always try to avoid them, but this board came by at an excellent price and I've wanted a weird IBM thing for a while, so this satisfied my weird IBM cravings...for now. This one didn't leak too bad, thankfully. But I must say, wow--these things are far WORSE than I remembered and imagined).

Similarly, is the inverse possible? Do SX FPUs support any fully 32-bit CPUs? I'm less-so interested in this configuration, but figured I would ask anyway out of sheer interest.

Thanks again in advance!