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AMD Navi Debuts RDNA Architecture

July 9, 2019

Author: David Kanter

RDNA is AMD’s first major new graphics architecture in seven years, offering redesigned compute units and a new cache hierarchy. The RDNA-based Navi GPU moves to 7nm technology at TSMC, beating Nvidia to that mark; it also upgrades most external interfaces, boosting performance per watt by 50% relative to its predecessor, Vega.

The first RDNA incarnation is the gaming-focused Radeon RX 5700-series, implementing a new programming model and a comprehensive set of upgrades over previous generations. The new RDNA compute units are designed for greater instruction-level parallelism, increasing per-clock performance (IPC) by about 25%, and they connect to a new multilevel cache that delivers greater bandwidth and efficiency. Despite the new capabilities, the architecture offers a compatibility mode to support software optimized for the earlier GCN architecture in Vega.

Navi is the industry’s first GPU with PCIe 4.0, doubling bandwidth to the host processor. Owing to Intel’s 10nm troubles, only AMD’s latest Ryzen processors offer this capability—unfortunate timing for AMD GPUs, but clearly a benefit for the company overall. AMD also upgraded the 256-bit memory interface to GDDR6, delivering up to 448GB/s. In addition, Navi is among the first GPUs manufactured in 7nm TSMC technology, helping it clock at nearly 2GHz while using a modest 251mm2.

Compared with Vega, Navi offers 14% greater performance, 2.3x better performance per area, and about 1.5x better performance per watt despite its commodity GDDR6. The choice of affordable memory is crucial, as the HBM2-based Vega cards were too expensive for most PC gamers.

Several AMD game-console customers have already announced they’ll use future RDNA variants, presumably paired with one of the company’s Zen 2 CPU cores. More surprisingly, Samsung recently licensed the RDNA architecture for deployment in tablets and phones, which we estimate will arrive in 2021 or 2022. 

Subscribers can view the full article in the Microprocessor Report.

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