After extensive research about what is possible with 2.5D interposer and 2.5D stacking, we concluded seems that a 4GB card would be the easiest thing to do. High Bandwidth Memory (HBM) uses a super fast 1024-bit wider interface and 1Gb/s per pin data-rate. This results with 128GB/s bandwidth per memory chip.
However, our sources who like to remain unnamed (for decades) are now telling Fudzilla that AMD planned to launch Fiji with 4GB of memory. The cards had been sampled and they are up and running for quite some time. The 4GB card needs four 8Gb chips (1GB) with a 1000MHz core clock, so you can end up with a total bandwidth of 512GB/s.
In order to put 8GB on the card you need eight 8Gbit chips (1GB per chip) with 1024GB/s bandwidth. This does sound like a beast and this is what an ultra-high-end card from AMD should look like. The downside is that the yield of 8GB cards is probably lower than with 4GB of cards and that they are more expensive to produce. The benefits are clear, as you get more bandwidth for super high settings at 4K and UHD (3840x2160), or 5K and beyond.
The decision to go for an 8GB Fiji rather than the planned 4GB version was in part attributed by Nvidia’s Titan X 12GB card announcement. This is just the first part of the story. One of the main reason is that the card is expected to perform so well in 4K gaming, that the 4GB frame buffer could impose a serious limitation.
Our sources are confident that the card is coming this summer, or early summer to be precise, but we don’t have a better date than that. It could be as early as Computex that starts in early June, but we would expect that it happens slightly later than that. Our friends from Sweclockers.com were reporting that the cards should come in Q2 2015 with 4GB HBM memory but I guess that this plan might be slghtly altered.
This could be quite interesting for gamers who can afford high-end hardware, as there will be a lot of competition from AMD to fight the Maxwell generation of Geforce and Titan X cards.