Though information about the technology has been making rounds over the last several weeks, GDDR5X technology finally gets official with an announcement from JEDEC this morning. The JEDEC Solid State Foundation is, as Wikipedia tells us, an "independent semiconductor engineering trade organization and standardization body" that is responsible for creating memory standards. Getting the official nod from the org means we are likely to see implementations of GDDR5X in the near future.
The press release is short and sweet. Take a look.
ARLINGTON, Va., USA – JANUARY 21, 2016 –JEDEC Solid State Technology Association, the global leader in the development of standards for the microelectronics industry, today announced the publication of JESD232 Graphics Double Data Rate (GDDR5X) SGRAM. Available for free download from the JEDEC website, the new memory standard is designed to satisfy the increasing need for more memory bandwidth in graphics, gaming, compute, and networking applications.
Derived from the widely adopted GDDR5 SGRAM JEDEC standard, GDDR5X specifies key elements related to the design and operability of memory chips for applications requiring very high memory bandwidth. With the intent to address the needs of high-performance applications demanding ever higher data rates, GDDR5X is targeting data rates of 10 to 14 Gb/s, a 2X increase over GDDR5. In order to allow a smooth transition from GDDR5, GDDR5X utilizes the same, proven pseudo open drain (POD) signaling as GDDR5.
“GDDR5X represents a significant leap forward for high end GPU design,” said Mian Quddus, JEDEC Board of Directors Chairman. “Its performance improvements over the prior standard will help enable the next generation of graphics and other high-performance applications.”
JEDEC claims that by using the same signaling type as GDDR5 but it is able to double the per-pin data rate to 10-14 Gb/s. In fact, based on leaked slides about GDDR5X from October, JEDEC actually calls GDDR5X an extension to GDDR5, not a new standard. How does GDDR5X reach these new speeds? By doubling the prefech from 32 bytes to 64 bytes. This will require a redesign of the memory controller for any processor that wants to integrate it.
Image source: VR-Zone.com
As for usable bandwidth, though information isn't quoted directly, it would likely see a much lower increase than we are seeing in the per-pin statements from the press release. Because the memory bus width would remain unchanged, and GDDR5X just grabs twice the chunk sizes in prefetch, we should expect an incremental change. No mention of power efficiency is mentioned either and that was one of the driving factors in the development of HBM.
Performance efficiency graph from AMD's HBM presentation
I am excited about any improvement in memory technology that will increase GPU performance, but I can tell you that from my conversations with both AMD and NVIDIA, no one appears to be jumping at the chance to integrate GDDR5X into upcoming graphics cards. That doesn't mean it won't happen with some version of Polaris or Pascal, but it seems that there may be concerns other than bandwidth that keep it from taking hold.