Review Index:

AMD Radeon HD 3870 and HD 3850 Review - RV670 at 55nm

Author: Ryan Shrout
Manufacturer: AMD

RV670 Architecture (cont'd)

The RV670 is also the first AMD GPU to implement support for PCI
Express 2.0 technology, the next evolutionary step in
interconnectivity.  Total bandwidth increases to 16 GB/s compared to
the 8 GB/s that current PCIe 1.0 would support though the benefits of
this move are pretty slim in single or even dual card graphics
implementations.  AMD claims that the move to 4-way CrossFire will
actually be able to take advantage of this large amount of bandwidth
and even that games like Call of Juarez see significant performance
boosts in 2-way CrossFire because of the move to PCIe 2.0.  We will be
doing some testing of our soon to see how that works out.

It is important to note, just for those that don't keep up with all
of our content here, that the HD 3800 PCIe 2.0 cards that we are
reviewing today are still compatible with existing PCIe 1.0
motherboards – no need to upgrade that part if you don't want to.

The final major architecture shift that we found on the RV670 core
is the inclusion of a new AMD PowerPlay functionality that is at least
a first to my knowledge; I haven't heard of anything similar on
NVIDIA's cards thus far.  Basically, the new RV670 core is self
monitoring in terms of GPU utilization and can dynamically clock itself
down to one of three levels depending on current usage.  The first
"step" is the most basic level where the clocks are set relatively low
and would primarily be used for 2D applications.  The second and third
"steps" increase the clock rates and performance levels with that third
and final spot being the all out 3D performance mode you'd expect.

AMD claims that this functionality will rid their cards of the
various problems associated with 2D and 3D clocks including being able
to run windowed games and benchmarks without affecting GPU performance
at all.  This change will also allow for some better power consumption
numbers while at idle and users will be able to see their estimated GPU
utilization in the control panel windows. While the usefulness for the
average gamer here is questionable, for some this could be a handy

New CrossFire Support

As I alluded to above, CrossFire is going to be seeing a
significant pair of upgrades timed with the release of the HD 3850 and
HD 3870 graphics cards. One we have already mentioned and that has been
floating around the rumor sites for months is for CrossFire X – this
will allow three-card and four-card CF configurations in addition to
the dual-card modes we are used to now. 

The issue here will be scaling and if adding a third or fourth card
into the mix will actually improve your gaming performance enough to
warrant the extra cost.  AMD seems more active in promoting their Quad
CrossFire to us right now than NVIDA is their 3-way SLI so it would
seem AMD might have a leg up in terms of software implementation.  But
in truth, this is something we won't have any way to know until we
actually get our hands on the hardware from both vendors.

An even more impressive step forward for me in the world of
multi-GPU graphics is the ability to use more than one monitor.  No
seriously, I'm excited about this.  And it's sad.  After years of SLI
and CrossFire from both NVIDIA and AMD, it looks like AMD is going to
be the first to allow you to run multi-GPU accelerated graphics while
maintaining your multi-monitor configurations!  AMD is marketing this
both as a way for multi-monitor gaming and as single-monitor gaming
with standard windows on the other screens – both of which are
exceptional in my book. 

On the next pages we'll get to the meat of the article including a
look at the new AMD ATI Radeon HD 3870 and 3850 graphics cards.