The AMD Radeon R9 380X will reportedly arrive to market in late October configured with 4GB of GDDR5 memory and a 256bit bus. We've already seen photos of the XFX Double Dissipation R9 380X leak online just a few days ago. However the previous leak did not include any information about the specifications of the card.







According to Fudzilla the new card will be released worldwide later next month and will feature 4GB of GDDR5 memory, Fudzilla does not claim to know any information beyond that. If these claims are accurate however, we can safely assume - from the 4GB capacity of the frame buffer - that the GPU will not feature a 384bit memory interface as was previously and widely believed.

Rumor Has It AMD Will Launch The R9 380X Next Month With 4GB Of Memory, But What Does That Tell Us?

Let's quickly go back to a card that exists outside of rumor circles today, the AMD Radeon R9 380. This $200 midrange graphics card features the same GPU configuration as the Tonga Pro based R9 285. Namely 1792 GCN cores, 112 Texture Mapping Units, 32 Render Output Units and finally a 256bit memory interface.

Tonga Pro is a cut down variant of the Tonga GPU, something AMD confirmed last year. Interestingly however Tonga XT , the full fledged variant, features 2048 GCN cores, 124 Texture Mapping Units, 32 Render Output Units and finally and most importantly a 384bit memory interface. AMD's Raja Koduri confirmed these specifications at a company event last year. A die shot of the Tonga GPU was also revealed three months ago for the first time and it again confirmed the existence of a 384bit memory interface. So it was widely speculated that AMD would launch a graphics card, namely an R9 285X, featuring Tonga XT with the previously outlined specs.







However the 285X never came to be so when AMD launched the R9 380 speculation regarding a Tonga XT variant was re-ignited. Especially since AMD left a wide enough price gap between the R9 380 and the R9 390 and did not announce any product under the 380X nomenclature when the 380 was released. This led many to believe that there's a possibility that we may finally see a product based on the full fledged Tonga XT GPU , with the entirety of its 384bit memory interface enabled, be part of the Radeon 300 series.

According to the latest rumor from Fudzilla however, we may never actually see a 384bit Tonga based graphics card. Interestingly, we found out that the PCB of the XFX graphics card pictured above is the same one used for the R9 380, a card that comes in 2GB and 4GB variants. A 384bit memory interface requires adding additional memory traces and this means a different PCB would be required. This finding supports Fudzilla's claim and indicates that the R9 380X will share the same memory bus spec as its little brother the R9 380.

Although all of this begs the question, what was the intention behind designing Tonga with a 384bit memory interface if the bus was never intended to be used in its entirety? According to our own internal die analysis, a 32bit memory interface slice is 3mm² large. This makes a 128bit memory interface segment 12mm² large. Which means that had the Tonga GPU been designed with a 256bit bus from the very beginning it would have been 347mm² large instead of 359mm². This would've made Tonga 3% smaller and 3% cheaper to make. Now that may not sound like a lot but a 3% cost reduction on a 30% profit margin isn't nothing and companies are certainly not out to squander profits. It all just does not sit very well and the frustrating part is that we may never find out why this decision was made.

AMD Tonga Based Radeon 300 Series Cards Specifications “Predicted”: