Previously, Samsung announced its future technology roadmap at the “Samsung Foundry Forum 2022”. Among them, Samsung confirmed that GDDR7 is under development, calling it a booster for future GPUs, with a rate of 36 Gbps, doubling the existing 18 Gbps GDDR6. Recently, Samsung introduced the specifications of GDDR7 in detail and confirmed that it will use the PAM3 signalling.
The existing GDDR6 uses the NRZ/PAM2 signalling, and the rate starts from 14 Gbps, and the fastest has reached 24 Gbps. When it was first put into production, the GDDR6 rate could not meet Nvidia’s demand for the Ampere architecture GPU, so Nvidia chose to cooperate with Micron to jointly develop GDDR6X using the PAM4 signalling, providing a rate between 18 Gbps and 23 Gbps, which is several quarters ahead of the JEDEC standard GDDR6.
Compared with NRZ/PAM2 providing 1-bit data transmission per cycle, and PAM4 providing 2-bit data transmission per cycle, PAM3 data transmission per cycle is 3 bits, which has been further improved. According to Samsung, GDDR7 is 25% more efficient and 25% more energy efficient. In addition to being used in GDDR7, PAM3 is also used in the upcoming Thunderbolt 4 and USB4 v2.0 specifications, enabling data transfer rates up to 80 Gbps.
Just like GDDR6 compared to GDDR5, the speed of GDDR7 is doubled compared to GDDR6. At the 256-bit bus and 36 Gbps rate, the bandwidth of GDDR7 will reach 1152 GB/s, and the bandwidth of 128-bit and 384-bit buses will be 576 GB/s and 1728 GB/s respectively at the same rate. This means that if future GPUs support GDDR7, they can easily break through the 1 TB/s mark.