VOGONS


First post, by W.x.

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Hello. To this date, I've thought, that i945gz motherboards do not have PCI express slot, well but today I've come across GA-945GZM-S2 and was quite confused, that it has full PCI express slot. So I've checked internet, and found out, where is the catch, it is interpreted through southbridge, and has only 4 lanes instead 16.
So I was thinking, how fast and compatible is this solution, in comparation to full i945 chipset, that has x16 lanes connected through northbridge.

Is it same compatible, or I can experience problems with PCI express graphic cards.
Main question... how much slower it is, in comparation to full x16 slot. I mean, with typical fast Pentium 4 in it, lets say 3 Ghz Pentium and Windows XP games of 2005-2008 era, do you experience any major slow down with lets say 7900 GTX?

Reply 1 of 7, by pentiumspeed

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The x4 lane is from southbridge if desired but not on this one you have for this model. The single PCIe slot is real x16 lanes from the northbridge. Checked the chipset wiki and gigabyte.

If motherboard maker wanted more lanes, they add second PCIe x4 slot from the southbridge, common practice even now.

Cheers,

Great Northern aka Canada.

Reply 2 of 7, by Horun

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pentiumspeed wrote on 2021-05-05, 00:01:

The x4 lane is from southbridge if desired but not on this one you have for this model. The single PCIe slot is real x16 lanes from the northbridge. Checked the chipset wiki and gigabyte.

If motherboard maker wanted more lanes, they add second PCIe x4 slot from the southbridge, common practice even now.

Cheers,

Yeah you are correct ! checked the datasheet and has a full 16x PCIe from northbridge, have seen some early boards where they route the lanes to two PCIe slots where each is just 8x but the GA-945GZM is not done that way.

Hate posting a reply and have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. 🤣 Second computer a 286 12Mhz with real IDE drive ! After that came 386, 486, Pentium, P.Pro and everything after....

Reply 3 of 7, by W.x.

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Here in specification, there is mentioned something, that I've thought is meant it is x4
So maybe slot looks like full x16 slot, it has only 4 lanes?

https://www.gigabyte.com/Motherboard/GA-945GZ … S2-rev-21/sp#sp

Expansion Slots1 PCI Express x 16 slot (@x4)
3 PCI slots

Reply 5 of 7, by Horun

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Odd ! Intel lists the 82945GZ as 16x PCIe https://ark.intel.com/content/www/us/en/ark/p … controller.html
but the datasheet says: PCI Express Graphics Interface (82945G/GC/P/PL only)
they had a board D945GZCC2 based on it but no other tech docs found, maybe it had issues with PCIe from the northbridge or all the lanes were dedicated to the onboard 950 graphics ????.

Hate posting a reply and have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. 🤣 Second computer a 286 12Mhz with real IDE drive ! After that came 386, 486, Pentium, P.Pro and everything after....

Reply 6 of 7, by W.x.

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Ok, I have another clue, it is only PCI express x4 mode Slot, that looks like PCI express x16, and it's not going through northbridge.
The reason why they made it the way, it's full PCI express slot is, so all graphic cards fit in. But it works only in x4 mode. That means probably no problem for low end graphic cards of that era, but midrange and high-end will be probably slowed down. Would like to test, how much drop performance it have with various graphic cards, and at what graphic card starting to be serious bottleneck, like more than 10-15%.

https://www.alza.sk/zakladni-deska-gigabyte-9 … m-s2-d72944.htm

(there is mentioned " jeden slot PCI Express x16 pre grafickú kartu (pracuje rýchlosťou x4).") Translation is, one slot PCI EXpress x 16 for graphic card (works with speed x4)

Reply 7 of 7, by W.x.

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All right, according this test, on Techpowerup, with PCI express x scaling, seems, performance loss even with modern highend card is not so big, actualy is small, around 5%. Which really suprise me.

https://www.techpowerup.com/review/nvidia-gef … xpress-scaling/

But maybe, in this case, as it's through some controller outside of chipset, compatibility will be even worse, and also slow-down.