http://www.startech.com/Cards-Adapters/Slot-Extension/PCI-X-to-x4-PCI-Express-Adapter-Card~PCIX1PEX4

Another odd component I found in my wandering through the web.

Allows PCIe cards to be used in PCI-X slots (like those used in G5 systems). Should also plug into G4 Powermacs (not sure if it would work though).

I saw a few Mac users arguing about the slots in the G4 PowerMac's and which type of PCI cards could and could not be used in them. There appears to be some disagreement between several users on the G3-G5 mailing list over at LoweEndMacs. Some users think they can use some PCI-X cards in the G4 MDD PowerMac's and others claim that they can't.

I don't know which group is right, but thought I would mention that argument in this thread, since it appeared to be related to the topic.

As near as I can tell, David, the expansion slots are 66MHz PCI-X.

I have no idea what they are, but there was a pretty good discussion about what cards you could use in a G4 MDD and the early G5 PowerMacs.

I guess some of the disagreement was because the G5's started with one PCI standard, switched to a better later standard, and then changed again in the last versions which had the PCIe slots and no longer had any AGP slot. (PCI, then later PCI-X and finally PCIe) I don't really know enough about the differences to care, as long as I use the right cards in my computers, so before putting a new PCI card into my G4 MDD, or my G5 PowerMac, I will make sure I am not going to damage anything.

I did not pay too much attention to the argument, but was a little amused that the guys arguing were sure that they were right and the other guy was wrong. Not sure who won, if anyone ever did.

[ Edited by amigadave 26.02.2012 - 14:43 ]

I'm sure our community would just confuse people like that.
For example, there is no OSX driver for the Soundblaster Live card we're using.

Currently, I'm looking at an Open Firmware SCSI controller card that can be used under OSX (even though it was designed for a Sun work station).

There are plenty of things that can be done with this hardware that wouldn't occur to most Mac users.

> As near as I can tell, David, the expansion slots are 66MHz PCI-X.

Just for future reference:

https://morph.zone/modules/newbb_plus/viewtopic.php?topic_id=8413&forum=11&start=7

As per Andreas' obviously correct observation - G4 Powermacs have 64 bit PCI slots.

33MGHx 64bit slot = PCI
66MHZ 64bit slot = PCI (Although some label these 66MHz PCI-X slots).
133MHz 64bit slot = PCI-X slot that actually conforms to the PCI-X stasndard

Except for operating frequency, all three of these appear similar.

> 66MHZ 64bit slot = PCI (Although some label these 66MHz PCI-X slots)

True. I still think that for 64-bit PCI operating at 66 MHz, both terms "PCI" and "PCI-X" are technically correct, because the fastest variant of the PCI spec was used as the basis and thus slowest variant of the PCI-X spec. So there is some overlapping actually.

> 133MHz 64bit slot = PCI-X slot that actually conforms to the
> PCI-X stasndard

...and so do the 100 MHz slot and the 66 MHz slot. It's just that the 66 MHz one conforms to both the PCI-X standard and the PCI standard, whereas those operating at higher clock speeds conform only to PCI-X (but which, to make it even more complicated, are backwards compatible to PCI cards with the same voltage).

> Except for operating frequency, all three of these appear similar.

True. Except that there're two physically different 64-bit PCI(-X) slot versions, one for 3.3 V and one for 5 V:

https://morph.zone/modules/newbb_plus/viewtopic.php?forum=3&topic_id=7638&start=40 (Wikipedia link)

I gain useful information from you all the time Andreas.
I just hope to retain it.
I contacted Startech.com to see what the requirements are for this adapter (in terms of operating frequency), but they have not sent a return message yet.
Obviously a G5 would have the necessary expansion slors (but then , if you wanted PCIe you could always move to a later model).

> I just hope to retain it.

I case you don't I guess I'll be there to call it back to your mind ;-)

> I contacted Startech.com to see what the requirements are for this adapter
> (in terms of operating frequency)

According to the installation guide (page 2), the card is 3.3 V and can be operated in a 133 MHz PCI-X 1.0 slot (default) or in a 33 MHz PCI 3.0 slot (via jumper setting).

Damn! I didn't think to look for that.

You are good!

So we could support low profile PCie cards.
Speed would be limited, but it should work.

Looking at this possibility, I'm beginning to wonder if I could manage to get a low profile 4650 to work under Ubuntu.

[ Edited by Jim 25.03.2012 - 15:27 ]

> So we could support low profile PCie cards. Speed would be limited, but it should work.

That would depend on whether the 64-bit PCI slots in the PowerMac G4 are really 3.3 V as required by the PCI 3.0 spec the card conforms to. Are they?

The only statement I could find from Apple was this

"The PCI slots can accommodate mixed voltage (5.0 V, 12 V, or 3.3 V ) cards with 32-bit or 64-bit data widths and a 33 MHz frequency."

And

"Install only expansion cards that come with Macintosh driver software and that comply with the PCI 2.1 standard."

So, apparently the slots conform to the 2.1 standard but do support 3.3 voltage.
I'm unsure if this would satisfy the requirements of this device.

> So, apparently the slots conform to the 2.1 standard but do support 3.3 voltage.
> I'm unsure if this would satisfy the requirements of this device.

From the connector that can be seen on images of the card, you could check if the card can physically fit into the PowerMac G4's 64-bit PCI slot.

Good idea. And...from an initial examination I'd have to say it won't fit.
The card is missing a notch in the middle section that my other PCI-X cards have that allows the cards to fit into the G4 expansion slots.
I know this is hard to picture from my description (I'll have to post photos later), but most PCI-X cards that will fit into a 64 bit PCI slot are keyed with four sections of pins.
This design only has three.
If there was another notch in the middle section (toward the rear) it would resemble my PCI-X disk controller cards (and it would fit).

So, I guess we have to assume this won't work.
Thanks for the simple test.

Edit - Pity that it wouldn't work. We ought to examine the ideaof using the full 64 bit PCI expansion more thoroughly.
While it doesn't provide anywhere near the bandwidth of PCI-X it is twice that of standard PCI.

132MB/s (PCI 32-bit bus @ 33MHz)
264MB/s (PCI 64-bit bus @ 33MHz)
800MB/s (PCI-X 64-bit bus @ 100MHz)
1056MB/s (PCI-X 64-bit bus @ 133MHz)





[ Edited by Jim 25.03.2012 - 21:15 ]

> from an initial examination I'd have to say it won't fit. The card is missing a notch
> in the middle section that my other PCI-X cards have that allows the cards to fit
> into the G4 expansion slots. [...] most PCI-X cards that will fit into a 64 bit PCI slot
> are keyed with four sections of pins. This design only has three. If there was another
> notch in the middle section (toward the rear) it would resemble my PCI-X disk
> controller cards (and it would fit).

64-bit PCI(-X) cards with 4 sections of pins are so called universal cards, meaning they can be operated in 5 V slots as well as in 3.3 V slots, with both kinds of slots having 3 sections of pins but with different section orders. The adapter card this thread is about has 3 pin sections so it's not universal, and the sections are arranged in a way that it's only operable in 3.3 V slots. Pure 5 V cards also have only 3 sections but with a different section order compared to 3.3 V cards. So if you say the adapter card wouldn't fit I conclude the 64-bit PCI slots of the PowerMac G4 must be 5 V ones.

> So, I guess we have to assume this won't work.

Yes, non-universal 3.3 V PCI(-X) cards cannot work in a 5 V PCI(-X) slot, neither physically nor electrically.

Thank you Andreas.
As the weekend runs down here in the US, you've (once again) helped to enhance my education.
I never expected to get this deeply into the PCI specification, but its been useful.
I'm also encouraged by how many 64 bit PCI accessories I'm finding. Its a pity that the G4 doesn't have 66MHz slots (as that would give it a four fold bandwidth advantage over standard PCi), but a 2 fold improvement in bandwidth is nothing to sneeze at.