AMD Radeon HD 6790 1GB Review – Barts hits $150

Barts sees a lower price

Barts hits the $150 price point

The Radeon HD 6790 1GB is a new $150 graphics cards based on the same Barts architecture found in the Radeon HD 6800-series of cards. Obviously there are fewer shader processors and lower clock speeds, though the 256-bit memory bus remains for better memory throughput. The goal is obvious: unseat the GTX 550 Ti (and the GTX 460) from NVIDIA as the best option for this price segment. Does it succeed?

Introduction

The hits just keep coming.  In a time of the year that is traditionally a bit slower (after CES but before Computex) the world of the graphics card continues to evolve and iterate at a blindly pace.  Since January we have seen the release of the GeForce GTX 560 Ti and the Radeon HD 6950 1GB cards, the Radeon HD 6990 4GB dual-GPU behemoth, the GeForce GTX 550 Ti budget card and even NVIDIA’s new GeForce GTX 590 dual-GPU card.  It has been a busy time for our GPU testing labs and the result is a GPU market that is both stronger and more confusing than ever. 

Today AMD is releasing another competitor to the ~$150 graphics card market with the Radeon HD 6790 1GB based on the Barts architecture we first tested with the HD 6800-series in October 2010.  When NVIDIA released the GTX 550 Ti in this same price field, AMD was dependent on the higher priced HD 6850 and the previous generation HD 5770 to hold its ground, both of which did so quite well.  The GTX 550 Ti was over priced at launch and is only now starting to see the correction needed to make it a viable selection.

AMD had different plans though and the Radeon HD 6790 will enter into the $150 space as the performance and pricing leader if neither of NVIDIA’s GeForce GTX 550 Ti or GTX 460 768MB can make a stand.

Radeon HD 6790 Specs and Reference Design

The new Radeon HD 6790 will sit in the current product stack from AMD just below the HD 6850 and above the currently available HD 5770 offerings.  For those that might have already done their research, yes there is indeed a Radeon HD 6770 being sold by AMD but it is only offered to OEMs for now while end users are left without it. 

According to this roadmap from AMD the HD 6790 will be the only 6700-series selection from AMD for the retail channel until at least Q3 of 2011. 

The technical details of the HD 6790 are simple to grasp once you understand that they are built on the Barts architecture rather than the Cayman designs seen in the HD 6900 cards.  Barts is in fact a modified version of the design used throughout the HD 5000-series of cards which in no way means that these products are disadvantaged.  The HD 6870 and HD 6850 have done a great job of providing improved performance over the 5000-series while lowering prices and offering new features. 

The Barts GPU consists of 1.7 billion transistors and the die used for the HD 6790 is basically the same as the one used for the HD 6850 and HD 6870 parts but with additional SIMD units disabled.  A rough diagram I made here illustrates the specification differences:

You can see that some of the features will remain the same including the 256-bit memory bus (something that was a problem for the GTX 560/550 GPUs) though we drop to 800 shader processors and 40 texture units.  The ROP count comes in at 16 meaning AA performance will drop a bit from that 6800 lineup. 

The fact that AMD chose to simply used re-binned GPUs and disable portions for the HD 6790 is interesting.  We might have imagined that they would build another GPU die rather than force board designers to deal with a 1.7 billion transistor GPU for a $150 card.  If AMD has a solid yield on these parts it might actually save them money in the long run rather than going through the process of another chip fab but just as likely is that AMD has seen quite a few raw die from TSMC that will support these specifications and no higher – now they have a part number to sell them under.

If you want a bit more refresher on the Barts GPU design and how it differs from the Radeon HD 5000-series lineup, take a quick look back at our Radeon HD 6800 launch article.   

The rest of the Radeon HD 6790 specifications are listed here including the 840 MHz clock speed and 1050 MHz memory speed of the reference design.  Both of those are listed as "up to" since add-in card partners are going to be given the option of lowering the speeds to move from dual 6-pin power connectors to a single.  Considering the GTX 550 Ti only requires a single power connector, it makes sense that some OEMs would ask for that as well.

Now, before we jump into looking at the reference card AMD sent for our performance evaluation I should note that ours looks VERY much like a Radeon HD 6850 card.  Retail offerings will likely be quite different though as AMD has said most vendors will be utilizing their own custom designs for the Barts architecture on this HD 6790 part.  You can expect retail HD 6790 cards to be smaller (and better looking) when they go on sale today.

Our early sample was pretty plain and basic – since other card manufacturers weren’t utilizing the reference design it was kept as plain as it was. 

Our reference sample, and I think most retail cards on the market, will utilize a pair of 6-pin power connections as this card just barely hits the 150 watt power consumption level.  Be sure you check on those clock speeds though as anything that uses only one power connector will probably be clocked under the reference speeds.

The external connection configuration continues to be a strong selling point for the AMD lineup of graphics cars with a pair of DVI outputs, two mini-DisplayPort connections and an HDMI port.

The Radeon HD 6790 supports single CrossFire configurations if you want to add in a second card down the line for added performance.

The Radeon HD 6790 (furthest back card) is similar in size to the Radeon HD 6850 though the power connectors have moved.  Again, all indications are that this reference card is going to be bigger and bulkier than what AMD’s partners come up with.

Remove the cover from the card reveals the standard heatsink and fan configuration from the HD 6800 series.  We aren’t diving too much into the cooling system here because, again, retail samples are going to be produced like this.