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Second Birth of CrossFire

It is only at the end of September 2005 that ATI at last solved all the problems with its new technology, so the 26-th of September should be considered the real birthday of CrossFire. As we said in our preview of this technology, the leading graphics developers are currently of opinion that the best results can only be achieved on a specially prepared platform. In other words, we should talk the platform at large rather than graphics card with its accessories when it comes to multi-chip technologies.

For example, NVIDIA’s SLI works the best with NVIDIA’s nForce4 SLI chipset, even though theoretically it can work on any other platform equipped with two PCI Express x16 slots. The same it true for CrossFire. It requires a special mainboard based on either of the two versions of the RADEON XPRESS 200 CrossFire Edition chipset: RD480 (for AMD) and RD400 (for Intel). Chipsets from other manufacturers will get certified, too, but so far these are the only CrossFire-compatible chipsets available. Let’s see what they are right now.

The RADEON XPRESS 200 CrossFire Edition chipsets have a classic two-chip architecture and support all modern processors from Intel and AMD. The RD400 North Bridge (for the LGA775 platform) supports a 1066MHz FSB and has a memory controller compatible with DDR400 (PC3200) as well as with DDR2-667. The R480 is simpler in design since AMD’s modern processors have an integrated memory controller. This chipset is in fact a PCI Express controller compatible with AMD’s processors that use a 1GHz HyperTransport bus.

The ATI chipsets both support 20 PCI Express lanes: 16 lanes for the graphics card slots, 2 lanes for PCI Express x1 slots or integrated controller that use this interface and 2 lanes more for connecting to ATI SB450 or ULi M1573/1575 South Bridges. We should note that although the RADEON XPRESS 200 CrossFire Edition is positioned as an advanced solution for enthusiasts, the capabilities of the ATI SB450 are rather humble in comparison with the NVIDIA nForce4 SLI:

 

nForce4 SLI

ATI RADEON XPRESS 200
CrossFire Edition

Architecture

Single-chip

North Bridge: ATI RD480
South Bridge: ATI SB450

Bus between
the chipset bridges

Not required

PCI Express x2 (1GB/s)

HyperTransport

16bit / 1GHz

16bit / 1GHz

PCI Express lanes

20 lanes

20 lanes

SLI/CrossFire support

Yes
(1 x PCI Express x16
=
2 x PCI Express x8)

Yes
(1 x PCI Express x16
=
2 x PCI Express x8)

PCI support

6 devices

7 devices

USB 2.0

10 ports

8 ports

Serial ATA

3 Gbit/s

1.5 Gbit/s

NCQ support

Yes

None

Serial ATA ports

4

4

Parallel ATA channels

2

2

RAID support

0, 1, 0+1

0, 1 (only for Serial ATA)

Ethernet

1 Gbit/s

None

Secure Networking Engine

Yes

None

Sound

8-channel AC97

High Definition Audio (Azalia)

The only advantage of the ATI chipset is its support of the High-Definition Audio standard (Azalia) whereas the NVIDIA chipset uses an ordinary AC’97 codec. The SB450 is inferior to the NVIDIA chipset in the rest of the parameters as it supports only 8 USB 2.0 ports (against the nForce4’s 10), doesn’t have an integrated network controller and doesn’t support the Serial ATA-II standard. It means the manufacturers of RADEON XPRESS 200-based mainboards will have to use an external PCI Express or PCI network controller and integrated appropriate chips (for example, Silicon Image SiI3132) to fully support the newest Serial ATA-II hard disk drives. The nForce4 SLI would allow building a mainboard by adding only a PHY Ethernet controller.

 
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