Ampere graphics cards: GDDR6X memory should achieve up to 21 GBit / s

The memory manufacturer Micron has in two (PDF) Documents (meanwhile offline) reveal some details about the upcoming GDDR6X for graphics cards: According to the two PDFs, the video memory reaches a speed of up to 21 GBit / s per pin, which is drastically higher than the previously usual 16 GBit / s of GDDR6. This is made possible by a modified coding process.

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GDDR6 with 15.5 GBit / s is used, for example, in Nvidia’s Geforce RTX 2080 Super, so 496 GByte / s bandwidth is achieved on a 256-bit interface. At 21 GBit / s, 672 GByte / s would be realizable, which corresponds to an increase of 35 percent. According to unconfirmed reports, Nvidia will rely on GDDR6X for future amp models with GA102 / GA104 chips: The data rate for the Geforce RTX 3090 with 384-bit interface should be almost 1 TByte / s.

In order to achieve 21 GBit / s, Micron changes for GDDR6X from NRZ (PAM2) to PAM4. This pulse amplitude modulation doubles the number of states per signal, which means that twice the amount of information can be transmitted per cycle. PAM4 is also used by PCIe Gen6 and previously in the network area for 200/400 GBit Ethernet chips. According to Micron, GDDR6X also requires 15 percent less energy (pJpB, picojoules per bit) despite 21 GBit / s compared to GDDR6 with 14 GBit / s, so efficiency increases with overall higher power consumption.

So far it looks like Nvidia will release three graphics cards with GDDR6X memory based on the GA102 chip: The Titan RTX (Ampere), the Geforce RTX 3090, alternatively called Geforce RTX 3080 Ti, and the Geforce RTX 3080. Unclear is so far how the interface and the amount of memory are. 384 bits with 48/24 GByte are conceivable for the Titan, for the RTX 3090 and RTX 3080 Nvidia could opt for 320 bits with 20/10 GByte. On September 1, 2020, CEO Jensen Huang will eventually receive the models by Livestream announce, this is titled as Geforce Special Event.