AMD Radeon HD3870/HD3870 X2 Video Technology Considerations (Page 1 of 1)
Written by
Rick Newcomb
Posted on: Mar 17, 2008 at 12:31pm
Section:
Hardware
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First of all X2 video technology or Dual-Core GPU video adapters are not the latest
graphic technology. ATI’s Rage Fury MAXX was a dual-GPU technology, which preceded
AMD’s (formerly ATI) Radeon technology video adapters. Both AMD and nVidia each have
products that boast about the gaming performance of their X2 Technology Dual-GPU Core
Video Adapters. This technology is not the newest concept in video graphics technology and
certainly is not without multiple and varying technical issues for giving the customer the
performance that they are paying for.
First, we need to define what has changed in graphics interface technology. All previous
graphics bus technology used a parallel interface to the graphics adapter. PCI-Express
(PCI-E) utilizes a full-duplex differential-pair serial interface technology, which is
controlled through a crossbar switch integrated on the motherboard, instead of utilizing
previous north/south bridge technologies. Each up/down communication pair is called a
lane. PCI-E 2.0 speed is 2x faster than PCI-E 1.1. The PCI-E 1.1 bus is a multi-lane
bi-directional serial interface bus, and each lane communicates at 250 MB/s in each
direction. Therefore, the x16 or 16-lane PCI-E 1.1 bus communicates at a raw speed of 250
MB/s (2.5 Giga-baud x 10-bits) x 16-lanes, which is 4.0 GB/s in each direction. There are
16-lanes up and 16-lanes down, which means the interface is full-duplex and produces a
bi-directional raw communications bandwidth of 8.0 GB/s. The PCI-E 2.0 bus communicates at
a raw 500 MB/s (5.0 Giga-baud x 10-bits) speed, 2 times faster than the 1.1 bus speed. The
PCI-E 2.0 raw bus speed is 8.0 GB/s per lane, in each direction, for a total raw
full-duplex communication bandwidth of 16 GB/s.
The latest “high-tech” video technologies include PCI-E 2.0, DirectX 10.1, which
are only supported in Microsoft Windows Vista O.S. with Service Pack 1 (SP1), but only if
you have the supporting motherboard and associated video adapter. The new built-in
features of DirectX 10.1 include 32-bit floating-point operations (instead of 16-bit
floating-point) and obligatory support of 4x FSAA.
As of March 5, 2008 AMD’s Radeon 3000 Series are the only video adapters that support
PCI-E 2.0 and DirectX 10.1.
Let’s look at the newly introduced PCI-E 2.0 bus. The simple fact is that PCI-E 2.0
is not fully realized without running in Microsoft Windows Vista with Service Pack 1
(SP1). Prior to SP1, Windows Vista supported DirectX 10.0 and Microsoft Windows XP Home
and Professional only supports DirectX 9.0c, which is a different issue all together.
The AMD Radeon HD3870 PCI-E 2.0 Video Adapter with 512 MB GDDR4 Video RAM running at an
impressive 1,125 MHz. and it is fully compatible with the new DirectX 10.1 Standard. The
single RV670 GPU operates at 775 MHz.
The AMD Radeon HD3870 X2 PCI-E 2.0 Video Adapter with 1,024 MB of GDDR3 Video RAM running
at 900 MHz., for an effective memory speed of 1,800 MHz. and it is fully compatible with
the new DirectX 10.1 Standard. The dual RV670 GPU’s each operate at 825 MHz. Each
RV670 GPU has a 256-bit interface which has it’s own 512 MB of video RAM dedicated to
it. The video interface is 256-bits-X2, or 512-bits wide.
Both video adapters are backward compatible with the previous PCI-E 1.1 Video Interface.
The HD3870 X2 is plug-compatible with the PCI-E 2.0 video bus, but the RV670 GPU’s
are not running at PCI-E 2.0 bus speed, due to the ExpressLane™ PEX 8547 PCI-Express
Switch device that connects the two RV670 GPU’s together, which performs the on-board
Crossfire functionality, but only operates at base PCI-E 1.1 speed, therefore, slowing
down the video adapter’s total bandwidth.
One new feature of this dual-GPU adapter is it’s ability to display 2 monitors while
in Crossfire mode. Earlier Crossfire and SLI video configurations could not run more than
a one monitor while in Crossfire or SLI modes. With the AMD Radeon HD3870 X2, you can
display the Windows Desktop on one monitor while playing a game in Full-Screen mode on the
second monitor. You can also run a game within a window and span across both monitors.
Loaded Temperature Ratings:
| HD3870: |
88 Deg. C (190.4 Deg. F) |
HD3870 X2: |
81 Deg. C (177.8 Deg. F) |
12 VDC Power Consumption Ratings:
| HD3870 (Idle): |
110 Watts (09.167 Amps) |
HD3870 X2 (Idle): |
151 Watts (12.667 Amps) |
| HD3870 (Loaded): |
222 Watts (18.500 Amps) |
HD3870 X2 (Loaded): |
357 Watts (29.750 Amps) |
There may be more coming, but not very soon. PCI-E 3.0 final
specification is due in 2009, but production products won’t be available until 2010.
Currently all of the PCI-E bus standards use a serial communication protocol that adds 25%
of the bandwidth for communication overhead (8-bits data + 2-bits framing = 10-bits
total), and if we look at the PCI-E 2.0 raw communication standard of 5.0 Giga-baud, we
find that we actually get 4.0 gbps data, or 80% of what we want. The PCI-E 3.0 bus will
remove the communication overhead and deliver 2 times what we now get from PCI-E 2.0, or
8.0 gbps bandwidth per lane.
EDIT: Updated 3/22/2008
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