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The card(s)
The Radeon HD 7790 is slated to be available for purchase on April 2 at a suggested e-tail price of $149. At "participating retailers," the card will be sold with a free copy of BioShock Infinite. Since the Radeon HD 7750 and 7770 were left out of the Never Settle Reloaded bundle, that's good to know.

AMD sent us a list of some of the Radeon HD 7790 variants its partners have in store. Here it is:

Officially, the Radeon HD 7790 is meant to run at an even 1GHz with 6Gbps memory. As you can tell from the list above, however, retail cards with above-reference clock speeds will be commonplace—possibly more so than standard designs. When briefing us about the 7790, AMD suggested that it gave partners an exceptional amount of leeway in designing their cards. The chipmaker also said we'll see versions of the 7790 with 2GB of GDDR5 memory, up from the default 1GB. None of those 2GB models are in the list above, though, and we weren't given a timetable for their arrival.

AMD eschewed sending us a reference board for our review. Instead, the company sent us Asus' Radeon HD 7790 DirectCU II, which is one of the nicer offerings coming in April. Asus expects to sell it for around $155, but exact pricing hasn't yet been set.

That big, heatpipe-laden dual-slot cooler almost dwarfs the stubby circuit board, which measures only 6.8" in length. Cooler included, the card is about 8.5" long. The DisplayPort, HDMI, and dual DVI outputs can drive up to six displays (provided you use a DisplayPort hub), and the card takes power from a single six-pin PCI Express connector. (Note that the PCIe connector is rotated, so that the clip faces the back of the circuit board. If it were in the usual position, the heatsink fins would be in the way.)

Unfortunately, we didn't get the DirectCU II until Tuesday, which gave us too little time to benchmark it. By then, we'd already started testing Sapphire's Radeon HD 7790, which FedEx delivered the day before.

The Sapphire card has the same 1075MHz core speed and 6.4Gbps memory speed as the Asus. It features a similar dual-fan cooler, albeit without conspicuous heat pipes, and it has the same 8.5" overall length and display output arrangement. The circuit board spans the whole length of the cooler, however, and the PCI Express power connector sits at the top of the card with the clip facing the front—a pretty common arrangement.

A farewell to the Radeon HD 7850 1GB
AMD's Radeon HD 7850 1GB came out in October. Since its launch, the card has wooed value-conscious gamers by delivering much of the performance of its 2GB namesake at a lower price—often as little as $160. We've recommend it in several of our system guides.

Now, sadly, the 7850 1GB is about to disappear from retail listings forever. The Radeon HD 7790 will be its de facto successor.

According to AMD, the 7850 1GB is going away because memory makers have stopped producing the 128MB GDDR5 chips it requires. The card has four 64-bit dual-channel memory controllers that must each be fed by two memory chips; it therefore needs eight 128MB chips to achieve a 1GB capacity. The 7790 doesn't have that problem. With only two 64-bit memory controllers, it can deliver the same 1GB capacity using larger, 256MB GDDR5 chips, which are still being made.

This disappearing act gives the 7790 some pretty big shoes to fill. GPUs with 128-bit memory interfaces don't often match the performance of their 256-bit siblings, especially when they're based on the same architecture. If the 7790 fails to deliver, folks could be forced to splurge for a Radeon HD 7850 2GB, which would set them back at least $180.

The competition
The Radeon HD 7790 won't just be trying to live up to the 7850 1GB's legacy. It will also face competition from higher-clocked versions of Nvidia's GeForce GTX 650 Ti, which are available in the same price range, as well as some of the old GeForce GTX 560 cards that remain on the market. We'll look at real-world benchmarks very soon, but before we do, let's take a quick look at theoretical numbers. The table below includes peak rates for both reference cards and the souped-up variants we've got in our labs.

Base
clock
(MHz)
Boost
clock
(MHz)
Peak
ROP rate
(Gpix/s)
Texture
filtering
int8/fp16
(Gtex/s)
Polygon
throughput
(Mtris/s)
Peak
shader
tflops
Memory
transfer
rate (GT/s)
Memory
bandwidth
(GB/s)
Radeon HD 7770 1000 N/A 16 40/20 1000 1.3 4.5 72
Radeon HD 7790 1000 N/A 16 56/28 2000 1.8 6.0 96
Sapphire Radeon HD 7790 1075 N/A 17 60/30 2150 1.9 6.4 102
Radeon HD 7850 1GB 860 N/A 28 55/28 1720 1.8 4.8 154
GeForce GTX 650 Ti 928 N/A 15 59/59 1856 1.4 5.4 86
Zotac GeForce GTX 650 Ti 2GB AMP! 1033 N/A 17 66/66 2066 1.6 6.2 99
GeForce GTX 560 810 N/A 26 45/45 1620 1.1 4.0 128
MSI GeForce GTX 560 Twin Frozr II 870 N/A 28 49/49 1760 1.2 4.2 134

Compared to the Radeon HD 7850 1GB, the 7790 in theory has similar texture filtering and shader performance, and it should offer even higher tessellation throughput. However, the 7790 has only three fifths the ROP rate, which means less resolve power for multisampled anti-aliasing, and two thirds the memory bandwidth. Those limitations may or may not affect real-world gaming performance, depending on the nature of the graphics workload.

The 7790 is more comparable to the GTX 650 Ti. On paper, these two cards have roughly equivalent ROP rates, polygon throughput, and memory bandwidth. The 7790 enjoys an advantage in shader throughput, while the 650 Ti promises better texture filtering performance, especially for fp16 texture formats. This contest is probably too close to call at this stage.

As for the old GTX 560, that card has the same advantages as the Radeon HD 7850 1GB—higher memory bandwidth and ROP rates—but it trails the 7790 in key rates like texture filtering, shader arithmetic, and polygon rasterization. The 7790 may come out ahead more often than not in newer games, especially those that use shader-based antialiasing techniques instead of MSAA.