You don't need two PCI-E 16X slots because there is no card that can use all of the 8x PCI-E's speed other than the SLI on a card... cards?
The Mac Pro has configurable PCI Express slots meaning that you can assign more PCI Express lanes to cards that need additional performance. You have a choice of four PCI Express Profiles:
• x16 Lane Graphics Slot + One x8 Lane and Two x1 Lane Slots
• x16 Lane Graphics Slot + Two x4 Lane and One x1 Lane Slots
• Three x8 Lane + One x1 Lane Slots
• Two x8 Lane + Two x4 Lane Slot
Other than an SLI on a card video cards 8x PCI-E is more than enough. THere are no cards that can use all of the 8X bus. (or whatever)
From Apple.com
Quote:
Mac Pro: About the PCI-E slots
PCI-E (Peripheral Component Interconnect-Express) is a newer implementation of PCI which uses a much faster physical-layer communications protocol than older PCI bus architectures.
Rather than using a bus as PCI did, PCI-E uses dedicated, unidirectional, point-to-point connections known as "lanes" to communicate with PCI-E devices.
The Mac Pro features four PCI-E 16-"lane" connectors on the main logic board. In PCI-E, these are known as "x16" slots. These can be used for PCI-E-compatible cards, like the ATI Radeon card that is available as a configure-to-order option in the Mac Pro.
PCI-E cards will work in slots that are at least as large as the card is. This means that the "x16" slots in the Mac Pro computer also supports "x1" and "x4" cards as well. However, all four slots cannot simultaneously support four cards that implement the same lane configuration. Only one slot actually has 16 lanes going to it—you can put a x16 card into a slot that is only using one lane and it will operate properly, but it will operate more slowly than the same card in a x4, x8 or x16 slot.
The Expansion Slot Utility, located in /System/Library/Core Services, allows you to configure the PCI-E expansion slots and how many lanes each slot will support, as illustrated below. This example shows a "x16" graphics card occupying the first slot, and the other slots are configured to support an "x1" card in slot two and "x4" cards in slots three and four. The example shows the other options available. When you have picked the appropriate configuration of slots to support your compliment of PCI-E cards, click the Save and Restart... button to implement the configuration.
You don't need two PCI-E 16X slots because there is no card that can use all of the 8x PCI-E's speed other than the SLI on a card... cards?
The Mac Pro has configurable PCI Express slots meaning that you can assign more PCI Express lanes to cards that need additional performance. You have a choice of four PCI Express Profiles:
? x16 Lane Graphics Slot + One x8 Lane and Two x1 Lane Slots
? x16 Lane Graphics Slot + Two x4 Lane and One x1 Lane Slots
? Three x8 Lane + One x1 Lane Slots
? Two x8 Lane + Two x4 Lane Slot
Other than an SLI on a card video cards 8x PCI-E is more than enough. THere are no cards that can use all of the 8X bus. (or whatever)
From Apple.com
the gforce 8800 cards run better with a x16 link then a x8 one.
Mac pro has 16 PCI Express lanes from the North Bridge + 8 for chip set to chip set link and 12 PCI Express lanes from the South Bridge.
I don't think that you can use all 12 SB lanes at the same time with out hitting a traffic bottleneck.
the gforce 8800 cards run better with a x16 link then a x8 one.
Mac pro has 16 PCI Express lanes from the North Bridge + 8 for chip set to chip set link and 12 PCI Express lanes from the South Bridge.
I don't think that you can use all 12 SB lanes at the same time with out hitting a traffic bottleneck.
Says who? If you get the numbers on what that card can push I'll bet it can not saturate an 8x lane.
There may be reason for that also, but I have read that you get better performance out of the 8x lanes using • Two x8 Lane + Two x4 Lane's than you do if you do not use the 4x option. Maybe that is the same problem PC's have run into with that option. Who knows?
Comments
The Mac Pro has configurable PCI Express slots meaning that you can assign more PCI Express lanes to cards that need additional performance. You have a choice of four PCI Express Profiles:
• x16 Lane Graphics Slot + One x8 Lane and Two x1 Lane Slots
• x16 Lane Graphics Slot + Two x4 Lane and One x1 Lane Slots
• Three x8 Lane + One x1 Lane Slots
• Two x8 Lane + Two x4 Lane Slot
Other than an SLI on a card video cards 8x PCI-E is more than enough. THere are no cards that can use all of the 8X bus. (or whatever)
From Apple.com
Mac Pro: About the PCI-E slots
PCI-E (Peripheral Component Interconnect-Express) is a newer implementation of PCI which uses a much faster physical-layer communications protocol than older PCI bus architectures.
Rather than using a bus as PCI did, PCI-E uses dedicated, unidirectional, point-to-point connections known as "lanes" to communicate with PCI-E devices.
The Mac Pro features four PCI-E 16-"lane" connectors on the main logic board. In PCI-E, these are known as "x16" slots. These can be used for PCI-E-compatible cards, like the ATI Radeon card that is available as a configure-to-order option in the Mac Pro.
PCI-E cards will work in slots that are at least as large as the card is. This means that the "x16" slots in the Mac Pro computer also supports "x1" and "x4" cards as well. However, all four slots cannot simultaneously support four cards that implement the same lane configuration. Only one slot actually has 16 lanes going to it—you can put a x16 card into a slot that is only using one lane and it will operate properly, but it will operate more slowly than the same card in a x4, x8 or x16 slot.
The Expansion Slot Utility, located in /System/Library/Core Services, allows you to configure the PCI-E expansion slots and how many lanes each slot will support, as illustrated below. This example shows a "x16" graphics card occupying the first slot, and the other slots are configured to support an "x1" card in slot two and "x4" cards in slots three and four. The example shows the other options available. When you have picked the appropriate configuration of slots to support your compliment of PCI-E cards, click the Save and Restart... button to implement the configuration.
You don't need two PCI-E 16X slots because there is no card that can use all of the 8x PCI-E's speed other than the SLI on a card... cards?
The Mac Pro has configurable PCI Express slots meaning that you can assign more PCI Express lanes to cards that need additional performance. You have a choice of four PCI Express Profiles:
? x16 Lane Graphics Slot + One x8 Lane and Two x1 Lane Slots
? x16 Lane Graphics Slot + Two x4 Lane and One x1 Lane Slots
? Three x8 Lane + One x1 Lane Slots
? Two x8 Lane + Two x4 Lane Slot
Other than an SLI on a card video cards 8x PCI-E is more than enough. THere are no cards that can use all of the 8X bus. (or whatever)
From Apple.com
the gforce 8800 cards run better with a x16 link then a x8 one.
Mac pro has 16 PCI Express lanes from the North Bridge + 8 for chip set to chip set link and 12 PCI Express lanes from the South Bridge.
I don't think that you can use all 12 SB lanes at the same time with out hitting a traffic bottleneck.
the gforce 8800 cards run better with a x16 link then a x8 one.
Mac pro has 16 PCI Express lanes from the North Bridge + 8 for chip set to chip set link and 12 PCI Express lanes from the South Bridge.
I don't think that you can use all 12 SB lanes at the same time with out hitting a traffic bottleneck.
Says who? If you get the numbers on what that card can push I'll bet it can not saturate an 8x lane.
There may be reason for that also, but I have read that you get better performance out of the 8x lanes using • Two x8 Lane + Two x4 Lane's than you do if you do not use the 4x option. Maybe that is the same problem PC's have run into with that option. Who knows?