ATI Radeon HD 3870 Graphics Card
PCB Design and Technical Characteristics
The ATI Radeon HD 3870 resembles the Radeon X1950 XTX as it uses a similar cooler and has the same dimensions. The PCB of the Radeon HD 3870 has a length of 23 centimeters (9 inches). This is almost 1 centimeter shorter than the Radeon HD 2900 (23.8cm).
The wiring of the Radeon HD 3870 is much simpler than that of the Radeon HD 2900, which is not surprising considering the 256-bit memory bus and the less potent power circuit that was not designed for a power draw higher than 150W. With the dismantled elements of the cooling system, the PCB looks almost empty, at least from the front side.
Unlike the 7-phase power circuit of the Radeon HD 2900, the Radeon HD 3870 uses a two-phase circuit. By our estimates, the Radeon HD 3870 has a peak consumption of 80-85W or less, so this power circuit should be able to power the GPU although it may be an obstacle to overclocking the latter. Each phase contains four Infineon BSC 042N03LS MOSFETs rated for a current of 95A and featuring SuperSO8 packaging with advanced thermal characteristics. Like on the Radeon HD 2600 XT GDDR4, the main controller is an uPI Semiconductor uP6201AQ. The uP6101BSA chip is responsible for the memory chips. The power circuit of the Radeon HD 3870 uses one external power connector, a standard 6-pin PCI Express 1.0 plug with a load capacity of 75W. Considering the 55nm tech process, this connector can hardly be under a load higher than 35-40W.
The ATI Radeon HD 3870 carries GDDR4 memory from Samsung. These K4U52324QE-BC08 chips have a capacity of 512Mb (16Mbx32), a voltage of 1.8V, and a rated frequency of 1200 (2400) MHz. This means a good stability reserve since the default memory frequency of the Radeon HD 3870 is 1125 (2250) MHz. Theoretically, this memory should be overclockable to its rated frequency at least and perhaps even higher. The total amount of memory on board the Radeon HD 3870 is 512 megabytes.
At the default memory frequency, the bandwidth of the Radeon HD 3870’s memory subsystem is 72GB/s. This is higher than that of the Nvidia GeForce 8800 GT 512MB but lower than the memory bandwidth of the ATI Radeon HD 2900 XT 512MB (105.6GB/s). But as you know from our tests, memory bandwidth is not a bottleneck for AMD’s solutions. The Radeon HD 3870 should not feel the lack of memory bandwidth in games.
The RV670 chip strikes you with the sheer size of its core. Incorporating 666 million transistors, it is only 192 sq. mm large (13.7x14mm). This is a good illustration of what the new 55nm tech process can do. Besides an ATI logo and a manufacturing date, the core doesn’t carry valuable information. Our sample of the chip dates the 39th week of 2007 (September 23-29). Although the domains of Radeon HD chips work at 26 different frequencies, only the main frequency of the chip is declared. It is 775MHz for the Radeon HD 3870. Die packaging lacks a protective frame, making you be cautious when installing or uninstalling the cooler to avoid damaging the core.
There is no difference from the ATI Radeon HD 2900 XT in terms of configuration: the GPU contains 320 ALUs grouped into 64 superscalar execution blocks with 5 ALUs in each. Four ALUs in such a block can perform simple instructions of the MAD type (Multiply + Add) but the fifth one is more complex and can execute transcendental instructions like SIN, COS, LOG, EXP, etc. Besides that, each execution processor contains a branch unit for flow control instructions (comparisons, loops, subroutine calls, etc). The single difference from the R600 is the support for the extended DirectX 10.1 capabilities (Shader Model 4.1). As we’ve seen in tests, the efficiency of this architecture in real-life applications depends directly on the optimization of the shader code translator in the driver for the particular application with its specific game engine. Otherwise, the performance of the Radeon HD is low since most of the ALUs remain idle.
The RV670 graphics core also incorporates 4 texture processors equivalent to 16 TMUs, 4 rasterization processors (render back-ends) equivalent to 16 ROPs, and a Compositing Engine for hardware CrossFire. Like the all previous Radeon cards with the Compositing Engine integrated into the core, the ATI Radeon HD 3870 has two CrossFire connectors and can be used in a multi-GPU subsystem consisting of four such cards. So, the purpose of the second CrossFire connector is now perfectly clear.
The RV670 contains not only an integrated audio core for outputting digital audio over the HDMI interface but also a full-featured UVD processor that was missing in the R600 chip. Now the ATI Radeon HD 3800 series offers the same options of hardware decoding and processing of HD video in H.264 and VC-1 formats as the ATI Radeon HD 2600 that has been the best solution in this area. The card is claimed to support HDMI 1.3, but the audio core seems to have the same capabilities as in the Radeon HD 2900: 5.1 audio output, 16bit/48kHz for non-compressed streams in PCM format, and no support for Dolby TrueHD/DTS-HD. You still need a special DVI-I → HDMI adapter, included with the card, to output audio over HDMI. This approach is handier than if the HDMI port were installed right on the card because it provokes no problems for owners of dual-monitor configurations.
As opposed to the ATI Radeon HD 2900 with its 9-pin connector, the ATI Radeon HD 3870 has a 7-pin mini-DIN connector for analog video output. The new series doesn’t carry a VIVO chip on board and even provides no place for installing such a chip. That’s quite logical because it is indeed an anachronism to support analog video input in S-Video/Composite format in 2008. Like on all modern graphics cards, the DVI-I ports support dual-link mode for resolutions up to 2560x1600.