How Do the PCI slots in Power Mac G4 MDD 2x 1.25Mhz work?

Joined
Sep 4, 2014
Messages
2
Reaction score
0
Points
1
Hi everyone, this is my first post here.

I have been trying to understand how the PCI slots in my Power Mac G4 MDD 2x 1.25Mhz work and it has been very frustrating. The official specs from apple say:
1) the graphics card is in a x4 AGP 2.0 slot (max theoretical throughput of 1066MB/s), and
2) the four pci slots are 64-bit, 33Mhz and all 4 slots share a second bus.

I have not been able to find anywhere that specifies which version of pci the slots are. A number of sites say the early G4s have slots that are pci version 2.1, which implies that the later ones have pci version 2.2, but I am unable to confirm that anywhere. Can anyone here confirm that the G4 MDD has pci version 2.2 slots?

I have also been trying to understand exactly how the throughput for the slots on the pci bus work. I THINK all the following are true statements (but am not sure and would really appreciate it if anyone here can confirm or deny any of this):

a) All cards in the four pci slots (and thus all devices plugged into these cards) share the theoretical maximum 266 MB/s throughput.
b) Each card/device utilizes the throughput separately, sequentially, through timing/interrupts.
c) Mixing cards of different Mhz on a single bus, slows the entire bus to the Mhz of the slowest card.
d) Mixing 64-bit and 32-bit cards on the same bus does NOT slow down speed.
e) 32-bit cards on the bus can only access 133 of the 266 max theoretical throughput; so if only 32-bit cards are on the bus the theoretical maximum throughput is 133 (not 266).Thus you cannot have one 32-bit card using 133 and another 32-bit card using another 133 of throughput at the same time.
f) If both 64-bit and 32-bit cards are on the bus, the 64-bit cards can access all 266 MB/s, but the 32-bit cards can still only access 133 MB/s. (Thus there is effectively two tiers of throughput, a bottom 133 accessible by any card, and a top 133 accessible only by the 64-bit cards).
g) pci 64-bit, 66Mhz cards are mostly backwards compatible (functioning as 32-bit, 33Mhz cards when plugged into a 64-bit, 33Mhz slot), and less frequently backwards compatible where they function as 64-bit, 33Mhz cards when plugged into a 64-bit, 33Mhz slot.
h) pci-X 64-bit, 66Mhz cards sometimes work the same way as described in g), but less often.

I would sincerely appreciate any info helping to confirm, clarify, or deny any of the above.

Thanks
Arthur Goodwin
 

pigoo3

Well-known member
Staff member
Admin
Joined
May 20, 2008
Messages
43,552
Reaction score
1,071
Points
113
Location
U.S.
Your Mac's Specs
2011 17" MBP 2.2ghz, 16gig ram, OS 10.11.6
My question back to you…

Do you have a specific purpose for gaining this knowledge on a 10+ year-old computer model…or is this purely an academic pursuit?

- Nick
 
OP
A
Joined
Sep 4, 2014
Messages
2
Reaction score
0
Points
1
Specifically in the case of my G4, the information will help inform me as to which RAID card I end up installing (or not installing) in my machine.

And, yes, I know my G4 is old. But it still works quite well for what it is being used for (it is the company's internal email server as well as used occasionally to access archived company documents that use some truly ancient programs) so I don't see any need to spend serious money on a replacement yet. But I had four old, but perfectly functional 50GB SLC SSDs come to me that would work in the G4 quite well (but would be too slow for our newer machines), especially if I can RAID them.

I also have a G3 blue and white that is still in service as well (it has the company database using OS 8.6 and is also used to access a lot of company records that are still on iomega zip disks), powered up continuously 24/7 for over 17 years (except for some brief periods during moves) and never once a problem with it (literally not once in all that time has the machine frozen up).

Best Regards,
Arthur Goodwin
 

pigoo3

Well-known member
Staff member
Admin
Joined
May 20, 2008
Messages
43,552
Reaction score
1,071
Points
113
Location
U.S.
Your Mac's Specs
2011 17" MBP 2.2ghz, 16gig ram, OS 10.11.6
Specifically in the case of my G4, the information will help inform me as to which RAID card I end up installing (or not installing) in my machine.

Ok…thanks for the info. Can you post some links to the RAID cards you are considering…and maybe we can answer the question reviewing the specs of the cards & the spec's of the computer.

If we went into a long discussion on how PCI slots work…we may answer that question…but that may or may not help us in actually solving the problem (getting a RAID card for the computer).

- Nick

p.s. Can you provide the specs of the Powermac G4 you have (there were a number of Mirror-Drive-Door Powermac G4's).
 
Joined
Aug 19, 2014
Messages
792
Reaction score
4
Points
18
You also may have some issues with the raid there is however another solution that can stabile the server and add more disk space you can install a 350 gig internal hard drive using a ide to sata adapter to speed up your machine instead of raid but be forewarned this machine is still very picky and finding a raid card that works most likely won't work even if you get the right card.
 

Shop Amazon


Shop for your Apple, Mac, iPhone and other computer products on Amazon.
We are a participant in the Amazon Services LLC Associates Program, an affiliate program designed to provide a means for us to earn fees by linking to Amazon and affiliated sites.
Top