ATI

Writing about the latest and greatest hardware is fun—I’m not going to lie. Getting hands-on with technology in the lab is practically a hobby, and I’m fairly confident that most enthusiasts would share that excitement surrounded by a lab full of tech.

But I’ll be the first to admit that $500 dual-GPU video cards and $1,000 Extreme Edition processors are Beluga caviar in a Big Mac world. There are some lucky gamers who really buy the pricey stuff. A majority, however, live vicariously through the reviews, and actually spends their money on components derived from high-end kit.

Fortunately, even the mid-range of the graphics market is full of excitement right now. Bargains pepper the $100-$200 range, from the Radeon HD 4830 to the Radeon HD 4850/GeForce GTS 250 and Radeon HD 4870/GeForce GTX 260.

The challenge faced by vendors like ATI and Nvidia, though, is that those inexpensive cards all center on the same GPUs—processors that actually begin life as potential top-shelf components powering boards like the GeForce GTX 285 and Radeon HD 4870. Dropping the engine from a $350 GTX 285 into a $180 GTX 260, for instance, has to be painful. Similarly, the slide from $180 Radeon HD 4870 to $130 Radeon HD 4830 isn’t exactly economical.

That’s why you see derivative mainstream GPUs. Think G94 to Nvidia’s G92 or RV620 to ATI’s RV670. They employ architectural elements from the full-strength GPU, but consume less die space. So long as ATI or Nvidia is able to sell enough of them to offset a separate chip design, they come out ahead.

A Mainstream Contender?

Enter ATI’s new Radeon HD 4770—the first GPU manufactured on a 40 nm process. As with the other models in the company’s HD 4000-series family, the HD 4770 is derived from the same popular RV770 design popularized by the Radeon HD 4870 and 4850 cards almost a year ago.

But this one sports a slightly different core arrangement. At the same time, it displaces ATI’s Radeon HD 4830, which centered on the same pricey RV770 GPU at 55 nm. Thus, we’ll be expecting at least comparable performance as we compare new to old.

If the Radeon HD 4770 is, in fact, able to stand up to the HD 4830, then the best news for value-oriented gamers will be this card’s price tag: $109. I don’t think I’ve ever used the word “impressive” in conjunction with something you’d normally find in the bargain bin. However, playable frame rates at 1920×1200 might just deserve such an adjective if this new mainstream board turns out to be a contender. It’d be a real coup for ATI too, given the massive market for $100 video cards, according to the same Mercury Research data we cited in the Radeon HD 4890 story.

Let’s dig a little deeper into the Radeon HD 4770’s innards for a glimpse at why this card has potential to be a winner.

Superficially, the Radeon HD 4770’s specs look fairly similar to ATI’s Radeon HD 4830. But they’re completely unique GPUs. For example, the 4830 centers on the familiar 956 million transistor RV770 with two of its 10 SIMD units disabled, yielding 640 total stream processors and the ability to filter 32 textured pixels per clock (down from 800 and 40, respectively).

ATI’s Radeon HD 4830 retained all four of the RV770’s render back-ends (each of which could process four pixels and 16 Z/stencil operations per clock—that’s why you see these cards spec’ed out with 16 ROPS). The memory controllers carried over as well, enabling the same 256-bit memory bus employed on Radeon HD 4850 and 4870 boards. The main difference, of course, was that the 4850 and 4830 were only armed with GDDR3, while the 4870 sported GDDR5.

In comparison, the Radeon HD 4770’s architecture employs an 826 million transistor GPU armed with the same number of SIMD units available (eight). It also boasts 640 stream processors (128×5) and 32 texture units. So, from a front-end view, RV740 looks a lot like the RV770 after it was chopped up to become Radeon HD 4830.

The full complement of ROPs carries over too, processing 16 pixels and 16 Z/stencil ops per clock. Where you’ll notice the most significant difference is the memory configuration—two of the four 64-bit controllers are cut, leaving a 128-bit pathway. Because those memory controllers are connected to the render back-ends via a hub, they don’t need to be mapped on a 1:1 basis.

Now, you’d assume the halved memory bus (down from 256-bits) would hammer performance. But ATI is outfitting the Radeon HD 4770 with 512 MB of GDDR5 memory, able to move twice as much data per clock versus GDDR3. So, the 4770’s throughput actually turns out to still be respectable for a mainstream part.

The shift to 40 nm has seemingly allowed ATI to push clocks on its Radeon HD 4770 significantly higher than what it was willing to offer on the 4830. Stock, the GPU runs at 750 MHz (versus the 4830’s 575 MHz).

Though the 800 MHz memory clock would appear slower than the 4830’s 900 MHz operating frequency, it’s important to remember that GDDR5 provides doubled I/O throughput. Of course, the card’s 128-bit counteracts those benefits. Whereas Radeon HD 4830 served up roughly 57.6 GB/s, the 4770 pushes 51.2 GB/s.

Another benefit of the 40 nm transition is reduced board power. ATI claims the 4770 is rated for a maximum 80W, putting it just over what a PCI Express slot is able to supply on its own. That’s well under the 110W cited for the Radeon HD 4850, though—a board that we’ll see is within the 4770’s performance crosshairs.

	Radeon HD 4850	Radeon HD 4830	Radeon HD 4770	Radeon HD 4670	GeForce GTS 250
Manufacturing Process	55 nm TSMC	55 nm TSMC	40 nm TSMC	55 nm TSMC	55 nm TSMC
SPs	800	640	640	320	128
Core Clock	625 MHz	575 MHz	750 MHz	750 MHz	738 MHz
Shader Clock	625 MHz	575 MHz	750 MHz	750 MHz	1,836 MHz
Memory Clock	1,000 MHz GDDR3	900 MHz GDDR3	800 MHz GDDR5	1,100 MHz GDDR4	1,100 MHz GDDR3
Frame Buffer	512 MB	512 MB	512 MB	512 MB	1 GB
Memory Bus Width	256-bit	256-bit	128-bit	128-bit	256-bit
ROPs	16	16	16	8	16
Price	~$129	~$90	$109	$80	~$129

In our Radeon HD 4890 review, we abstained from publishing overclocking results to avoid mis-representing what a retail sample of the card could really do.

This time around, however, we were simply too curious about the 40 nm shift and what it could mean for enthusiasts who don’t mind cranking the knobs on their brand new graphics cards. Bear in mind that this is still an early sample of the HD 4770—your mileage may vary.

With stock clocks of 750/800 MHz as our reference point, we settled on a stable 830/850 MHz combination of frequencies in 3D mode, maxing out ATI’s Overdrive utility. And while the core automatically scales back to 250 MHz on the Windows desktop, memory maintains a constant 850 MHz when it’s overclocked.

Performance increases attributable to overclocking are minor, but certainly measurable. In Far Cry 2, the best returns fall just short of 10%.The same goes for Stalker, another one of the most GPU-limited tests in our suite.

Cooling

ATI readily admits that the Radeon HD 4770’s reference cooling solution was borrowed from its old 3800-series boards. Apparently, the less-aggressive dual-slot cooler enables cost savings versus single-slot solutions—but who’s to say? This thing still employs a large copper heatsink, heatpipes, and a covered shroud, so we’re honestly not sure where the supposed savings really comes from.

But by the time you’re ready to buy a new graphics card, you might not even need to worry about it. Wave one of Radeon HD 4770s will be the bog standard reference cards, as expected; dual-slot coolers, two dual-link DVI outputs, and so on. The wave after will be the ones tweaked by board partners (and will likely include models with single-slot coolers, juiced clocks, and special bundles).

Of course, that’s when you’ll need to keep an eye out for price. Spend too much trying to doll up something that was good enough in its stock form and you’ll find yourself priced right out of the product’s original value proposition. A Radeon HD 4770 priced at $109 is what we have on the bench today, so assume reference across the board in your own comparisons.

One thing we do need to mention: the first Radeon HD 4770 that arrived had an early BIOS with a slightly “off” cooling ramp. It’d heat up, spin to full duty cycle for two seconds, then drop back down to idle. This was fixed by a second card sent out by ATI, along with a note stating all of the boards appearing at retail starting April 28^th would include the fixed BIOS. We were also able to fix the issue by manually keying in the fan speed.