Als je de marketing slides van HBM bekijkt dan is het nogal een verschil. Volgens de officiele lezing is HBM 400% sneller dan GDDR5 en is HBM2 op zijn beurt weer 100% sneller. Het stroomverbruik daalt respectievelijk met 48% en 8%. Dat scheelt nogal wat. Met die getallen durf ik GDDR5 best inferieur te noemen.
Gamer nexus had er vorig jaar een stukje over, waarbij ook over 512 bit werd gepraat.
We also know that an RX 480 uses 40-50W for its 8GB, which is already a significant increase in power consumption per-GB over Vega: FE. The RX 480 also has a memory bandwidth of 256GB/s with 8GB GDDR5, versus Vega 64’s 484GB/s. The result is increased bandwidth, the same capacity, and lower power consumption, but at higher cost to build. In order for an RX 480 to hypothetically reach similar bandwidth, power consumption would increase significantly. Buildzoid calculates that a hypothetical 384-bit GDDR5 bus on Polaris architecture would push 60-75W, and an imaginary 512-bit bus would do 80-100W. For this reason alone, HBM2 saves AMD from high power budget that would otherwise be spent solely on memory. This comes down to architectural decisions made years ago by AMD, which are most readily solved for with HBM2, as HBM2 provides greater bandwidth per watt than GDDR5. HBM is effectively a necessity to make Vega at least somewhat power efficient while keeping the higher memory bandwidth. Imagine Vega 56, 64, or FE drawing an additional 70-100W – the world wouldn’t have it, and it’d be among the hottest cards since the GTX 480 or R9 290X.
The Vega architecture is clearly starved by memory bandwidth, too: Overclocking HBM2 alone shows this, as its gains are greater than just core clock increases. AMD didn’t have another choice but to go with HBM2, even though costs would be roughly one-third on the memory. GDDR5 might be possible, but not without blowing power consumption through the roof or losing on performance by limiting bandwidth.
AMD provided GN with a statement pertaining to choices revolving around HBM2, which reads as follows:
“AMD chose HBM2 memory for Vega because this advanced memory technology has clear benefits on multiple fronts. HBM2 is a second-generation product that offers nearly twice the bandwidth per pin of first-generation HBM thanks to various refinements.
“As we noted in the Vega whitepaper, HBM2 offers over 3x the bandwidth per watt compared to GDDR5. Each stack of HBM2 has a wide, dedicated 1024-bit interface, allowing the memory devices to run at relatively low clock speeds while delivering tremendous bandwidth. Also, thanks to die stacking and the use of an interposer, Vega with HBM2 achieves a 75% smaller physical footprint for the GPU die plus memories versus a comparable GDDR5 solution.
“The combination of high bandwidth, excellent power efficiency, and a compact physical footprint made HBM2 a clear choice for Vega. We have no plans to step back to GDDR5.”
AMD ended up opting for two stacks of HBM2 on the current Vega cards, which limits its bandwidth to Fury X bandwidth (2x 1024-bit Vega vs. 4x 1024-bit Fury X), ultimately, but AMD does benefit in the bandwidth-per-watt category. That’s the crux of this decision.
Wat dat betreft is de performance lead van Nvidia eigenlijk best indrukwekkend. De 1070 moest het immers ook met trage en onzuinige GDDR5 doen (de 1080 kreeg het snellere GDDR5X). Ondanks dat zijn de Nvidia kaarten flink zuiniger en, buiten DX12 om, min of meer even snel als de Vega56. Stel je voor dat Nvidia de 1070 GDDR5X had gegeven en de 1080 HBM2...
[Reactie gewijzigd door sdk1985 op 10 april 2018 15:52]