First post, by donkom
- Rank
- Newbie
Hey everyone,
I'm trying to wrap my head around a few concepts I never fully understood before - the difference between 64-bit PCI and PCI-X, including bus frequencies and voltages.
Here's what I've learned in the past few days, PLEASE correct anything incorrect and offer additional information. There isn't a lot to go on.
- 64-bit PCI was an extension of the 32-bit PCI bus, and made available in 33mhz and 66mhz variants, sometimes on the same board.
- 66mhz versions were only 3.3 volt, 33mhz versions were either 5v or 3.3v (though I cannot currently find evidence of 33mhz 3.3v slots)
- PCI-X started at 66mhz and went up from there, offering 3.3v
That's where things get murky. The Wikipedia page for PCI-X seems to use 64-bit PCI interchangeably with PCI-X ( https://en.wikipedia.org/wiki/PCI-X ), as do most resources online. I have questions.
There's a paragraph here ( https://www.meinbergglobal.com/english/info/pci.htm ) that I found interesting:
"However, due to electrical limitations on the length of the wires between the slots the PCI-X specs allow only up to two slots to be connected to a single bus. So if there are more PCI-X slots available then they are normally connected to several independent buses, each bus with 2 slots."
And yet with 64-bit PCI, we have motherboards like the Tyan Thunder 2500 that was equipped with SIX 64-bit PCI slots, some 3.3v 66mhz and some 5v 33mhz. I don't believe they would have made three separate buses just for this. Here's the manual for that motherboard: ftp://ftp.tyan.com/manuals/m_s1867_100.pdf
(side note: anyone have one of these boards they are willing to sell? I'll give it a good home. Seriously.)
So, there are differences. But people seem to throw the terms together under the same umbrella as if they are the same. Yet, no one has been able to answer this question: Can I use a PCI-X card in a 3.3v 66mhz 64-bit PCI card slot? Do these standards overlap with an identical communication protocol?
Many PCI-X cards can operate in a standard 32-bit PCI slot with some reduced bandwidth/functionality, which makes me believe the underlying standard/protocol is similar - but no one ever talks about 64-bit PCI and it's successor PCI-X, and where the line is drawn between them. There's even weirder connections like this one which I deemed to be incompatible: https://www.ebay.com/itm/333655665804 (it looks similar to the ASUS Media Bus, but was used for a proprietary RAID card. Note the larger spacing for the notch at the end).
Furthermore, there's this weird beast: http://www.pridopia.co.uk/8114.html
Does that actually mean I can plug in a PCIe card in some bastardized fashion into a 64-bit PCI slot? What a monstrosity. I want it.