Introduction - do read this.
CF
CrossFireX preview
A bit of history, if you
will.
Released in September 2005, ATI brought its own multi-GPU
technology - where two graphics cards are leveraged in tandem to
increase performance - to the desktop, to compete with NVIDIA's SLI.
Dubbed CrossFire, it allowed the user to purchase a master card and
regular slave card, based on the same underlying GPU, and team them
together to produce up to 2x the base card's performance. The entire
point of CrossFire was to promote additional performance,
which
could either equate to higher frame-rates at a particular resolution or
higher image-quality settings, for the same resolution, than a single
card's.
Support for the nascent CrossFire technology necessitated the provision
of a motherboard capable of running the two PCI-Express cards - be it
ATI or Intel chipset-based - albeit with split-lane PCIe arrangements.
The two cards were connected via an external cable and the maximum
supported resolution was 1,600x1,200 - limited by the specifications of
the compositing chip
Higher performance was achieved by a variety of rendering modes, and
the actual scalability of a gaming title was dependent on
just how well the engine queued up frames and how well-tuned the
CATALYST driver was.
ATI created profiles for popular games but the
unwieldy nature of the setup, together with the need for a master card,
ensured that first-generation (two-card) CrossFire was strictly an
enthusiast-only
adventure.
ATI's next CrossFire evolution abandoned the inelegant master/slave
arrangement and provided inter-card communication via the PCIe bus.
Limited in pure bandwidth stakes when compared to NVIDIA's
bridge-attaching SLI solution, CrossFire finally became a viable
solution with the introduction of the Radeon X1950 Pro GPU, released in
October 2006, reviewed over
here,
and integrated the compositing engine - which takes the frame data
produced by one card and composites it with the other, to produce the
final output - for internal CrossFire, meaning that the previous
master/slave relationship became moot.
Subsequent series of GPUs carried the internal compositing engine and,
thinking of higher-end cards, were attached to one another via an
NVIDIA-like bridge fashion, with the interconnect providing data output
right up to a screen-busting 2,560x2,048.
ATI, now part of AMD, upgraded CrossFire support on the
recently-released
Radeon
HD 3800-series
of GPUs by providing higher
inter-card bandwidth and the provision for two connectors, paving the
way for three- and four-card support.
NVIDIA, meanwhile, had beaten ATI to the performance three-way punch
with
its three-way SLI, reserved for its high-end GeForce 8800 GTX and Ultra
GPUs.
ATI, though, formally launched its highest-performing desktop product,
Radeon
HD 3870 X2, in January 2008, which leveraged two Radeon HD
3870 GPUs -
albeit
with slightly different clockspeeds - on to one card: internal
CrossFire on a single PCB. One could hook a couple of these together to
form a four-GPU subsystem, but doing so required a specific driver that
was still a work in progress at that time.
This brief history lesson brings us nicely to CrossFire
X - the latest
incarnation of ATI's multi-GPU technology that hardware-launched with
the
Spider
platform in November 2007.
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