[sillywalk]

If I recall, the 486-SX was a DX with the FPU disabled (or it was defective). There were 25,& 33MHZ versions.. I think the 66MHZ were "DX2"

[dspillett]

IIRC AMD put out a chip that officially ran at 66MHz without clock doubling, though obviously you needed a motherboard (and RAM) capable of running at that rate.