Renesas Debuts Client and Registering Clock Drivers for Server Designs

July 06, 2023 by Aaron Carman

The newest Renesas DDR5 chips are claimed to boost transfer speeds for both the server and the client.

Adding to its DDR5 momentum, Renesas has announced two new DDR5 DIMM chips for faster server and client performance in emerging applications. This announcement comes amid concerns of approaching the upper limit of DDR4 memory and falling subject to the von Neumann bottleneck, making these contributions valuable in continuing the momentum toward faster processing.


The Renesas RCD and CKD chips

The Renesas RCD and CKD chips each address memory performance and transfer speeds at different locations in the HPC ecosystem. Image used courtesy of Renesas

Renesas’ announcement covers two new pieces of memory support: the Gen 3 registering clock driver (RCD) and a new client clock driver (CKD). Each chip plays a crucial (although very different) role in high-performance computing systems. This article summarizes the metrics of the chips and provides insight into how they can impact both server- and client-side computing.


Server-side Clock Driver

The RCD is targeted primarily for enterprise-grade server applications where memory bandwidth can be a critical bottleneck. The RG5R364 chips buffer the command/address (CA) bus, chip selects, and the clock between the DRAM controller and the memory. An additional BCOM bus for load-reduced DIMM (LRDIMM) is also included to control the data buffers.


The Renesas RCD

The Renesas RCD improves reliability by buffering and driving the memory clock, preventing parasitic effects from impacting operations. Image used courtesy of Renesas

While it may not directly boost DIMM performance in typical conditions, the RCD allows server-grade memory to maintain its maximum 6400 MT/s performance across all temperature and load conditions, improving reliability and computation speed in nonideal scenarios. Furthermore, the integration with other DIMM peripherals, such as SPD hubs, temperature sensors, and power management ICs, gives server memory designers a bevy of new options.

The release of the Gen 3 RCD marks another available RCD chip supporting transfer speeds up to 6400 MT/s, with Rambus releasing its Gen 3 RCD shortly after adding SPD and temperature ICs to its portfolio as well. A key difference between the two chips is the support for LRDIMM in the Renesas design. However, it is still too early to fully compare the performance of the two. 


DDR5 Client Memory

While the RCD addresses server-side memory speeds, Renesas is also aiming to boost client-side DDR5 DIMMs with its first-generation CKD. Similar to the RCD, the CKD is designed to provide a buffer between the input and output clocks, providing more robustness for high-speed and next-gen applications.


The Renesas CKD

The Renesas CKD adds a new block to client-side DIMMs, providing improved performance across a wider operating range along with supporting hardware. Image used courtesy of Renesas

The CKD supports input clock rates up to 3600 MHz, with an associated maximum transfer speed of 7200 MT/s. Designers can leverage three operating modes where either one, both, or neither of the two input clocks can drive the corresponding output pairs with a PLL. I2C and I3C buses also provide access to internal control registers for device configuration.

Both the RCD and CKD are in sampling in FCBGA and FCCSP packages and are expected to be available in volume in the first half of 2024. In addition, Renesas has combined the new chips with other supporting hardware as part of its Winning Combinations portfolio, speeding up time-to-market for designs using Renesas parts.


DDR5 for All

While these advancements from Renesas may only be directly beneficial to engineers designing DIMMs, they may ultimately impact all who touch the HPC market, either as designers or users. The improved transfer speeds, coupled with higher processing power, will ultimately result in better computing performance for memory-intense applications.

Indicated by both the Renesas and Rambus innovations, it seems that DDR5 is becoming a more prominent feature for both high-performance client- and server-side applications, resulting in higher performance and efficiency that could save terawatts of power. Whether or not the Renesas RCD and CKD appear in the latest or highest-performing DIMMs, the move toward increased DDR5 performance and prevalence is a net benefit to all.