We're already well acquainted with AMD's Radeon HD 7870 and 7850 graphics cards. We studied them, and the Pitcairn graphics processors that dwell within them, about three weeks ago. In that initial encounter, we learned that these cards have all the makings of successors to the popular Radeon HD 6800 series: similar-sized GPUs and memory interfaces, with lower power requirements. The newcomers are quite a bit faster, too. Thanks to a new 28-nm chip fabrication process and a revised graphics architecture, dubbed GCN, they even outpace the old Radeon HD 6900 series cards, which are based on larger chips.
Unfortunately for bargain hunters, AMD has priced the Radeon HD 7850 and 7870 at $249 and $349, respectively, well above the $180-240 price range the 6800 series occupied when it arrived in October 2010. Whispers around the industry suggest the higher prices can be attributed the limited supply of 28-nm wafers coming from TSMC, the Taiwanese foundry that manufactures chips for AMD, Nvidia, and other firms like Qualcomm. Nvidia charges a pretty penny for its freshly released GeForce GTX 680, too, which has a smaller GPU and the same memory interface width as the GeForce GTX 560 Ti yet sells for twice as much.
In a nutshell, the 7800-series Radeons deliver only slightly better performance per dollar than the prior-gen Radeon HD 6900 cards, though they have the potential to be much cheaper. Not much of a consolation prize, I know.
The new Radeons therefore have to play up their other advantages in order to seduce prospective buyers. One of those advantages is a rather substantial amount of overclocking headroom. Our reference Radeon HD 7870, which came to us directly from AMD, had no trouble climbing from its stock 1000MHz clock speed all the way up to a blistering 1275MHz. We were able to overclock its memory from 1200MHz to 1375MHz, as well. Those settings yielded substantial performance gains without huge increases in power consumption.
Unsurprisingly, board makers have jumped on the opportunity to serve up customized, higher-clocked versions of the Radeon HD 7870 and Radeon HD 7850. (Such cards are sometimes referred to as "overclocked in the box," but that's a bit of a misnomer, since no overclocking actually takes place. The cards ship with the higher clocks and are fully supported by the manufacturer.) Today, we're looking at a couple of hot-clocked cards, both hailing from XFX.
Behold, the XFX Double D HD 7870 Black Edition and Double D HD 7850 Black Edition:
Which one is the 7850, and which one is the 7870, you ask? Well, have a look at a couple more pictures, and see if you can guess:
Yes, the only identifiable difference is the writing on the top of the cards. The two products otherwise look identical, with the same board-and-cooler length (9.76"), the same number of six-pin PCI Express power connectors (two), and the same cluster of display outputs (dual DVI, dual mini DisplayPort, and a single HDMI port). Both cards also feature the same cooler, whose four copper heat pipes make direct contact with the GPU and spread out into an array of aluminum fins. The whole shindig is kept chilly by a pair of "dust-proof" fans. In this case, "dust-proof" means dust shouldn't get inside the motor, not that you won't have miniature dust bunnies collecting on the fan blades after a few months. XFX claims its cooler design enables lower temperatures and noise levels than the competition.
XFX uses a similar shroud on its Double D HD 7970 Black Edition, which performed exceptionally in our testing, but the underlying coolers are actually quite different. The 7970 features a vapor-chamber heatsink with a copper base and, from what we can tell, more aluminum fins. XFX's Double D branding seems to refer to the presence of dual fans and not to a specific cooler design.
XFX touts the card's other perks, such as solid-state capacitors, ferrite iron core chokes, and a circuit board containing two ounces of copper. And it offers lifetime warranty coverage, provided you register the cards on its website within 30 days of purchase; otherwise, the warranty drops to two years.
Those are the similarities. Now for the differences: the Double D HD 7870 Black Edition runs at 1050MHz, and its memory ticks away at 1250MHz for an effective transfer rate of 5000 MT/s. That's a step above the GPU and memory speeds of the reference AMD card, which are 1000MHz and 1200MHz, respectively. The difference between the Double D HD 7850 Black Edition and the reference Radeon HD 7850 are greater: the Black Edition runs at 975MHz with a 1250MHz memory speed, while the AMD card is clocked at 860/1200MHz.
The 7870 and 7850 Black Edition otherwise have the same internal resources as their reference counterparts: 1280 ALUs and 80 texture units on the 7870, and 1024 ALUs backed by 64 texture units on the 7850. Both are complemented by 2GB of video RAM.
As you'd expect, those clock speed increases don't come free of charge. XFX prices the 7850 Black Edition at $279, about 30 bucks above stock-clocked cards. The 7870 Black Edition will set you back a cool $389, which is equivalent to a $40 markup over vanilla models. XFX is asking a fair bit for speed increases that, based on what we've seen, may be easily attainable with cheaper offerings and a little manual tweaking. However, the XFX cards have fancy coolers and might have further overclocking headroom in store. Let's have a look, shall we?