AMD Radeon HD 3800 Series. Tests of the "low-end" HD3850
Date: 04.12.2007
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By: Dmitry Sofronov, Vladimir Romanchenko.
Almost half a year has passed. To be more precise, there has passed half a year and one day, and AMD has officially announced a new generation of 3D graphics called ATI Radeon HD 3800 family. Today, the time for shuffling rumors on RV670XT chips has come to an end, and now it's high time we got acquainted with the first-hand official information. Even more than that, today we are presenting not only the details of the new Radeon HD 3800 architecture and its comparison versus the previous Radeon HD 2000 version, but now we also have the opportunity to estimate the performance of a real specimen based on the new chips in real applications.
To date, the new Radeon HD 3800 family is presented by the new two processors - Radeon HD 3870 and Radeon HD 3850. Don't be confused by the unusual digital indices of the chips. The thing is, from this GPU generation onward AMD has announced a migration towards a new principle of marking: the first digit in the index stands for the generation, the second one – for the processor family, with the remaining two left for marking the performance of the chip - the higher the performance, the greater is the two-digit number.
Therefore, the first digit in the marking of Radeon HD 3870, for instance, stands for the third generation of the Unified Shader architecture (the second generation are ATI Radeon HD 2900 chipset, while the first generation was implemented in the Xenos chip for the XBOX 360); the second digit stands for the family (we can assume that if there is "8", why shouldn't "5", "6", or "3" appear, with memory buses of various widths and/or "cut-down" versions of the core), and the last two digits imply manipulations within the family.
 We can say that this way AMD is solving two issues at one fling. First, it get rid of all these numerous add-on indices like XT, Pro which lately confuse even specialists. Secondly, it brings the awareness of graphic chips to the analogy with the marking of CPUs which was introduced by AMD a bit earlier and has already proven its efficiency. It looks like marketing people at AMD have done a really good job.
And what about the development engineers? To be brief, the key innovations in the new generations of Radeon HD 3800 chips, which make them stand out from the previous generation R600 are a migration to the finer, more precise 55-nm process technology with a simultaneous reduction in the overall number of transistors; emergence of support for DirectX 10.1, the PCI Express 2.0 bus, and ATI CrossFireX configurations. Along with these, the new generation of chips offers a Unified Video Decoder substantially reworked as part of ATI Avivo HD, as well as the power-saving technology ATI PowerPlay first implemented for desktop PCs.
That is really in brief. To make the key innovations of the Radeon HD 3800 series and its distinctions from the predecessors look more vivid, we bring them in as a comparative table.
AMD ATI Radeon GPUs: main specifications |
| GPU |
Radeon HD 3870 |
Radeon HD 3850 |
Radeon HD 2900 XT |
| Q-ty of transistors |
666 mln |
700 mln |
| Process technology |
55 nm |
80 nm |
| Streaming processors |
320 |
| Texture units |
16 |
| Rendering buffers |
16 |
| Core clock speed |
775 MHz and higher |
670 MHz |
740 MHz |
| Memory clock speed |
2.25 GHz |
1.66 GHz |
1.65 GHz |
| Performance (Multiply-Add) |
497+ GigaFLOPS |
428 GigaFLOPS |
475 GigaFLOPS |
| Support for the system bus |
PCI Express 2.0
PCI Express x16 |
PCI Express x16 |
| Supported DirectX version |
10.1 |
10 |
| Hardware tesselation unit |
Yes |
| UVD |
Yes |
None |
| ATI PowerPlay |
Yes |
None |
We now can move directly to a detailed examination of the novelties of the Radeon HD 3800 family, and we first should note that the key architectural specifications of the RV670 graphic processors have remained without any special changes. The base of the graphic core is the same unified shader architecture. It is based on the so-called dispatch processor that distributes task threads into 64 superscalar streaming processors, each in turn R600 is equipped with a new dispatch processor that distributes streams among 64 superscalar streaming processors, each having 5 independent discrete stream processing units and branching units, which altogether makes up 320 shader unified processors in 5-component SPUs (Streaming Processing Units) which provide processing up to 5 Multiply-Add instructions per cycle, plus one of the processors is able processing more advanced instructions (SIN/COS/LOG). The dynamic balance of loading the shader processors with vertex, geometrical, and pixel operations is provided automatically by the hardware scheduler.
There is a complete analogy with R600 that is also seen in the same texture units which are in charge of fetching texture and vertex data – they are also four, each having four fetching units and four addressing units thus making 16 altogether; there is the same number of ROP – also 16. There is also analogy in the organization of two-tier L1 and L2 caches. For details of the fundamentals of architecture, read our article Radeon HD2900XT – hopes that haven't come true, and fundamental innovations, and we go on talking about the innovations of this summer.
Finishing with the narration of the ATI Radeon HD 3800 core, we have to admit that its "cycle-wise" performance is declared at a level equivalent to that of ATI Radeon HD 2900. I note it separately that the design of the new core offers a 256-bit memory interface with an internal 512-bit circular bus. Indeed, the previous core had a twice wider 512-bit memory interface with the internal 1024-bit circular bus, however, such a reduction of internal and external performance of the memory controller has been made up for in RV670 with other amendments. The 8-channel 64-bit mode of memory organization for this chip is unavailable, but the lack of 4-channel 64-bit mode is more than compensated by the efficient 8-channel 32-bit mode, combined with higher clock speeds of the memory in higher-end card of the new family of chips, plus improvements in the arbitration logic of the memory controller.
At that, we would like to recall the substantial reduction in the number of transistors: they are 666 mln in the new RV670 core versus 700 mln in R600. That is, about 34 mln less than that with the functionality preserved and even a number of novelties implemented. At the stage of tests, we even put forward an idea that engineers at AMD decided to get rid of a hardware tesselation unit within the chip. Basically, giving up the use of hardware tesselation which makes sense only if game producers support that and provided there is a mandatory support for Microsoft DirectX in the list of requirements would be justified at this stage. However, the new core has a programmable tesselation module, and the matter of sharp reduction in the number of transistors with a vivid gain in functionality is still open.
At least, engineers at AMD asset that these are the consequences of successful redesign of the architecture. Indeed, for half a year that has passed since the announcement of R600, engineers at AMD have spent the time efficiently at elimination of architectural bottlenecks, and not only that. Among the key changes in the architecture, we already mentioned a migration to the 55-nm process technology. If there were no other changes, the redesign from the previous 80-nm process technology would appear to be a good move towards the reduction of power consumption in new GPU.
At AMD, they also accentuate the fact that the PowerPlay power consumption technology has been implemented in the core of RV670, but we can regard it as new only for the "desktop" graphic chips, since it made its debut earlier in a number of solutions for mobile PCs, like ATI Mobility Radeon HD 2300, HD 2400, and HD 2600. Recall that the ATI PowerPlay technology provides a reduction of clock speed as the load goes down and even "powers off" the temporarily idle elements of the chip. Therefore, substantial reduction in the TDP of Radeon HD 3800 family chips as compared to the predecessors should give credit to the migration to the new 55-nm process technology, TSMC with its successful struggle against the leak currents, as well as the redesign of chips, and addition of all the power-saving capabilities to the architecture.
Emphasizing the novelties implemented in the ATI Radeon HD 3800 family, we should mention support for DirectX 10.1, thus with support for the Shader Model 4.1. This first and substantial enough update to DirectX 10 is anticipated with the advent of Windows Vista SP1 in about the first quarter of 2008. The list of additional capabilities of DirectX 10.1 is long enough - there will be advanced features for programming, lighting, anti-aliasing, etc. Video cards based on Radeon HD 3800 are ready for these novelties - it is now turn of the game and application producers.
Another important innovation which is still in the plans for most of us is about migration to the PCI Express 2.0 bus. We should assume that demand for video cards offering the advanced functionality will be generated with the advent of new motherboards that offer support for the PCI Express 2.0 bus, in complete analogy with the migration from AGP 8x (which is still going on). In terms of that, Radeon HD 3800 chips are ready for such a migration.
Today, implementation of the more advanced ATI Avivo HD technology with the Universal Video Decoder in Radeon HD 3800 family chips is more topical. The UVD/UVD+ option integrated in Radeon HD 3800 chips provides a full-featured hardware decoding of the HD signals of H.264 and VC-1 formats (the VC-1 was decoded still in the previous UVD version), which is most topical for unloading the CPU while playing back modern HD DVD/Blu-ray video.
Along with other traditional output capabilities, video cards on new chips offer support for the HDMI and HDCP, with a full-fledged support for HDMI high-resolution displays - the protected content can be played on screens up to 2560x1600.
Finally, the ATI CrossFireX technology allows support for up to four (two, three) video cards of the Radeon HD 3800 family on a single motherboard, support for up to 8 monitors; with coordinated control of performance, Extended Desktop mode, and other interesting features. As an example of operating 8 monitors, we bring in demo video clip recorded from Microsoft Flight Simulator.
To be fair, we should note that it makes sense talking about ATI CrossFireX in more detail only once all the platform components which support this operation have appeared. Nevertheless, we should already now point to such interesting novelties like unlocking the GPU with ATI Catalyst; modes of protection and rolling back to safe modes; manual setting of clock speeds for the core and the memory, as well as the auto-configuration feature that enables "safe" overclocking within stable limits. By the way, configuring the ATI CrossFireX with ATI Catalyst 7.10 provides handling both DirectX 9 and DirectX 10 applications in the "Compatible AFR" mode.
This is about all the theoretical information which we would like to share prior to moving to the practical tests of a real video card in real applications. Apart from the re-branding of ATI logos which has been announced today, we should mention the new name Radeon HD 3870 X2 that dashed cursorily in the new specifications. That lets us hope for new graphic cards with a dual chip to appear in the forthcoming year.
As a final touch to this introduction, we are presenting a comparative table of specifications for video cards built on the new chips whose start of deliveries was promised to commence as of today onwards.
ATI Radeon 3800 family chips: main specifications |
| GPU |
Radeon HD 3870 |
Radeon HD 3850 |
| Memory bus |
256 bit |
| Clock speed and memory type |
1.2 GHz GDDR4 |
900 MHz GDDR3 |
| Memory capacity |
512 Mb |
256 (512) MB |
| Form Factor |
2 slots |
1 slot |
| Power socket |
6-pin PCIe |
| Peak power consumption of the card |
105 W |
95 W |
| Standard noise |
34 dBA |
31 dBA |
| Interfaces |
2x Dual-link DVI with HDCP (HDMI + audio via an adapter) + HDTV Out |
| ATI CrossFireX mode |
2, 3, or 4 video cards |
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