64 PCWorld AUGUST 2019REVIEWS AMD RADEON RX 5700 AND 5700 XT
speeds for Navi GPUs: Base and boost are
what you’d expect, defining the upper and
lower limits. But AMD’s also listing a “game
clock,” that represents “the minimum
expected GPU clock when running gaming
applications.” It warns that those speeds
aren’t guaranteed or even set in the VBIOS,
but is instead simply “a guide used to set
expectations with gamers.” Nvidia handles its
listed Boost clocks in the same manner, so if
you want to compare GeForce cards against
the Radeon RX 5700’s speeds, look there.
Note that it says “minimum expected GPU
clock,” and that they were obtained using
AMD’s blower-style reference cards. In the
Full Nerd interview referenced near the top of
this article, Radeon boss Scott Herkelman
acknowledged that overclocked, custom-
cooled models by AMD partners could very
well push gaming speeds closer to the Boost
clock rating, as you’d expect.
The Radeon RX 5700 and RX 5700 XTalso change the underlying memory
configuration. The Radeon VII and Vega
GPUs utilized second-generation high-
bandwidth memory stacks, continuing the
HBM push that AMD spearheaded with the
Fury X (go.pcworld.com/fryx) in 2015. AMD
switched to traditional GDDR6 memory for
these new cards, matching Nvidia’s current
GeForce lineup.
For Nvidia, the switch from GDDR5 to
GDDR6 provided enormous throughput
benefit thanks to GDDR6’s much faster
speeds. It’s more of a lateral move
performance-wise for AMD, because HBM2’s
2,048-bit wide memory interface allowed for
excellent memory bandwidth speeds. The
Navi cards we’re reviewing here hit 448GB/
second of memory bandwidth thanks to their
8GB capacity and 256-bit bus.
“We are not ruling out HBM2 in our
roadmap,” Herkelman told me in our Full
Nerd interview. “We will continue to support
that in markets
that make sense.”
For these Radeon
RX 5700 cards in
particular,
GDDR6 lets AMD
“hit better price
points [and] still
get great
performance”
while being more
widely adopted