CrossFire – Những điều bạn cần biết về công nghệ chạy đa GPU của AMD

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Surely you have heard of Nvidia’s SLI technology. But, AMD was not to be outdone when it launched CrossFire to run its multi-GPU. In this article, we will learn about it together.

Overview

CrossFire (or CrossFireX), is the name of the multi-GPU support technology developed by ATi Technologies, now AMD. This technology allows up to 4 GPUs to be linked together in the same computer, increasing graphics processing capabilities. For related technologies on laptops with separate cards, it is called AMD Hybrid Graphics.

AMD stopped using this name in 2017. However, they still support this technology for applications using DirectX 11.

CrossFire generations

1st generation

CrossFire first appeared to the public on September 27, 2005. To use it, you need to have a compatible mainboard and 2 Radeon graphics cards using the PCIe protocol. The Radeon x800, x850, x1800, and x1900 models all come in two versions: regular and Crossfire Edition. The only difference between the two versions is that Crossfire Edition will have the “Master” feature. This feature is essentially just adding 5 image synthesis chips, helping to combine the output of both cards. To do this, after buying a Crossfire Edition card, you will have to buy an identical card but in the regular version. The Master card will come with a DVI-Y adapter, with 1 connector plugged into the DVI port on both cards. The other end will plug into the screen.

This generation has quite a few limitations in terms of bandwidth. And CRT users who want to play games on large LCD screens, or simply at high resolution, will run into problems.

2nd Generation (Software CrossFire)

When used on the “CrossFire Xpress 3200” chipset mainboard, you will no longer need a master card to run CF (except the X1900 series). On the mainboard, the two cards will communicate with each other via the PCI Express bus. This is quite similar to the CF on the X1300 model, but the Xpress 3200 has been designed for communication between the two cards with low latency and high bandwidth. Although there is no improvement in performance, this is considered a marketing victory for ATi.

Generation 3 (CrossFireX)

With the launch of the X1950 Pro model, ATi has completely redesigned the way CrossFire connects. Thereby, they eliminated the DVI-Y adapter and configured 2 Master/Slave cards. In its place is a completely new connection standard called CFBI (CrossFire Bridge Interconnect). The 2 cards will be connected via a flat cable with the 2 ends attached to the connection points on the top edge of each card. Thereby eliminating the need to use a Master card, giving maximum performance. Sounds a lot like SLI, right?

This change was fully utilized when CrossFireX was introduced. Another interesting thing is that in the HD 3800 series, you can run CrossFire 2 different cards with their clock controller. Therefore, it is possible to eliminate the need to use two identical cards.

Another step forward in CrossFire’s connectivity facility is the placement of two GPUs on the same board. This was realized in early 2008 with the HD3870 X2 and then the HD4870 X2. When you install two together, you will only need to plug in a single cable.

​ Alike

Both CF and SLI have the same weakness: they do not improve 3D performance much. In some cases, it can also cause frame drops due to the coding of the application you are using. This weakness is inherent in GPU-intensive systems. It is often seen when running an application at low resolution. When using CrossFire with the AFR method, the actual frame count may be lower than the frame count shown in the benchmark software. Worse, in some cases, the results are worse than when running one card. This phenomenon is called microphone stuttering and it also appears on SLI.

In the old days, both CrossFire and SLI needed a bridge. And you also need a power supply strong enough to power all the cards plugged into the computer.

Strengths compared to SLI

CrossFire only needs 2 cards with GPUs of the same generation to be used. This allows users with limited budgets to buy 2 different cards and still enjoy the performance benefits. For newer card models, only 2 card models of the same series can CrossFire with each other. For example: an HD 5850 can run CrossFire with the HD 5870, but cannot crossfire with the HD 5770. SLI requires you to have a card with the same GPU and the same NSX to be able to use it.

Weakness

CrossFire’s fatal weakness is that it only works in Fullscreen mode. When running in Windowed/Borderless mode, separate support will be required. In addition, in generation 1, you needed a DVI-Y connection which was quite cumbersome because the PCI Express bandwidth at that time could not meet the needs of running CrossFire.

Epilogue

CrossFire could have been a breakthrough technology. But unfortunately, when not many applications currently support it, it is gradually sinking into oblivion.

Are any of you still running or have you ever run CrossFire on your system? Please share your experiences in the comment section below.

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