But all else is not equal, so recommendations aren’t quite that cut and dry. Nvidia preaches the gospels of PhysX and CUDA, with an occasional verse about GeForce 3D Vision. ATI sings the hymns of DirectX 10.1 and Stream. Depending on which company you put your faith in, one of those two messages is going to sound a little sweeter.

 

Right now, the two are in full-scale conversion mode, trying to get everyone they can to pitch in their tithing for a little gaming salvation. Just as PhysX and CUDA are starting to take hold with high-profile titles enabling support, so too are software developers paying more attention to DirectX 10.1.

 

As a superset of DirectX 10, DirectX 10.1 includes a handful of quality-enhancing features that, in some cases, will run on DirectX 10 hardware, but at a performance hit. For instance, the Gather4 function fetches four samples (2×2) where a DirectX 10 part would only be able to fetch one. The result should be more realistic shadow maps and better performance. The Stalker: Clear Sky demo lets us test that theory with a toggled check-box to enable or disable DirectX 10.1.

 

 

Our first test pits all of the Radeon HD 4800-series cards in this story against each other, without MSAA for alpha-tested objects enabled. At 1920×1200, performance is fairly similar across the board, with all test cases except the Radeon HD 4870 X2 demonstrating small gains by moving to DirectX 10.1.

 

 

We then turned on 4x MSAA for alpha-tested objects and re-ran the numbers, this time at 1680×1050, in an attempt to maintain somewhat reasonable frame rates. This time, a majority of the test cases show DirectX 10.1 incurring a small performance hit. Is the performance tradeoff worthwhile? For that, we’ll need to make an image quality comparison from within the game itself.

 

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Up top you’ll find the screen capture provided by ATI, right up against a wall, demonstrating that the DirectX 10.1 shadows are softer and arguably more realistic. I ran all over the opening area of the game trying to find a clear example of the difference made by DirectX 10.1 shadows and just couldn’t come up with an indisputable best-case scenario. Even by reloading saved points, it was impossible to generate the exact same scene twice. Nevertheless, given the option of enabling DirectX 10.1 and not seeing a significant performance hit, you might as well turn the feature on.

 

 

 

 

 

With the Game Developer’s Conference recently past, ATI had a handful of DX 10.1 titles to discuss during its briefing, besides Stalker. Tom Clancy’s HAWX looks like a fun title with DX 10.1 screen space ambient occlusion and accelerated Gaussian shadows. There were two other lesser-known titles, plus the UNiGiNE game engine, on which several upcoming titles are purportedly based.

 

As of right now, DirectX 10.1 isn’t making a huge impact, but because it will become a subset of DirectX 11, you can expect the extra features being enabled right now to work moving forward in Windows 7. The same couldn’t be said for the disruptive shift from DirectX 9/XP to DirectX 10/Vista.

DirectX 10.1

DirectX 10

Spurce:http://www.tomshardware.com/reviews/radeon-hd-4890,2262-3.html

Where it differs most is clock speed—on its core and memory bus. Stock Radeon HD 4870s employed a 750 MHz engine and quad data rate memory running at 900 MHz. This new offering cruises at 850 MHz with 975 MHz GDDR5 memory.

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In order to get those elevated frequencies, ATI had to do some work to the GPU’s core. In short, the RV770 consistently had issues clocking beyond a certain point—a fact that was evident in many of our System Builder Marathon overclocking attempts, which generally fell short at the same frequency range.

The company’s engineers went in looking for slow electrical paths and re-wired them in such a way that they wouldn’t inhibit faster frequencies. Physically, the GPU is fractions of a millimeter larger due to additional capacitors that clean up power to the chip. But it remains the same ol’ design popularized mid-2008. As you can see from the table above, clock-for-clock RV770 and RV790 perform nearly-identically clock-for-clock.

	Radeon HD 4870 X2	Radeon HD 4890	Radeon HD 4870	GeForce GTX 285	GeForce GTX 260 Core 216
Manufacturing Process	55 nm TSMC	55 nm TSMC	55 nm TSMC	55 nm TSMC	55 nm TSMC
SPs	1,600 (2 x 800)	800	800	240	216
Core Clock	750 MHz	850 MHz	750 MHz	648 MHz	576 MHz
Shader Clock	750 MHz	850 MHz	750 MHz	1,476 MHz	1,242 MHz
Memory Clock	900 MHz GDDR5	975 MHz GDDR5	900 MHz GDDR5	1,242 MHz GDDR3	999 MHz GDDR3
Frame Buffer	2 x 1 GB	1 GB	1 GB / 512 MB	1 GB	896 MB
Memory Bus Width	2 x 256-bit	256-bit	256-bit	512-bit	448-bit
ROPs	2 x 16	16	16	32	28
Price	$400	$249	~$180	$340	~$180

Not surprisingly, the 4890 card itself is easily mistaken for a Radeon HD 4870. They’re the same length; they both employ dual-slot coolers and the same dual-DVI plus video output configuration. Subtle differences set the two cards apart, giving away the fact that these two boards are indeed based on different GPUs.  And despite the slight increase in load power consumption as a result of the 4890’s higher clock speed, ATI still gets away arming the card with two six-pin auxiliary power connectors.

 

As of right now, ATI doesn’t have plans for a Radeon HD 4890 X2 variant, as it likely wouldn’t offer much more than a Radeon HD 4870 X2. And the chip’s extra full-load power consumption would create additional heat that’d need to be cooled.

Overclocking

The principal benefit from moving from HD 4870 to HD 4890 would, in our minds, be overclocking headroom. Stock-to-stock, you’re looking at a 100 MHz frequency increase. However, right out of the gate, ATI’s board partners will be shipping juiced models running a 50 MHz-faster core clock. According to AMD, the new GPU layout should be capable of going even faster than that.

The driver’s Overdrive sub-routine now offers a maximum frequency of 1 GHz, suggesting ATI is fairly comfortable with its enthusiast customers running at that speed. Rather than push our card that high and run the risk of misrepresenting performance with a hand-picked sample, however, we ran our HIS Radeon HD 4890 Turbo sample at its stock 900/975 MHz speeds and compared it to the reference clocks ATI is officially launching.

Upping the core clocks to 900 MHz is good for gains between five and 10% at 2560×1600. One of these factory-overclocked boards undoubtedly enhances the value of ATI’s Radeon HD 4890 versus the 4870 1 GB. However, there will undoubtedly be an additional price premium over the reference cards, too, softening the worth of that extra performance to some degree.

Source: http://www.tomshardware.com/reviews/radeon-hd-4890,2262-2.html