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Understanding CORSAIR CUDIMMs: A Technical Deep Dive

The new CORSAIR CUDIMMs (Clocked Unbuffered Dual In-line Memory Modules) are engineered for high-performance computing. Built upon the latest DDR5 architecture, these memory modules are designed to handle the demanding workloads of gaming, content creation, and professional applications. All while still being backwards compatible (at 6,000MT/s or below) with previously available DDR5 platforms.

Speeds beyond UDIMM

Based on the same DDR5 architecture, CUDIMMs enhance what is offered by the DDR5 UDIMM architecture.

Higher Bandwidth

Until now, the fastest DDR5 UDIMMs paired with a good CPU and high-end dual-DIMM motherboard could reach 8,000MT/s. CUDIMMs raise that bar and on Intel® Z890 motherboards, the memory speed can go over 9,000MT/s. This leap in data transfer speed is key for users running applications sensitive to memory bandwidth or engaging in memory overclocking.

CORSAIR CUDIMMs achieve these high speeds through a combination of carefully selected DRAM ICs, a new 10-layer PCB, and the new Clock Driver IC (CKD).

The Role of CKD (Clock Driver Chip)

One of the most significant innovations with CUDIMMs is the integration of a Clock Driver IC (CKD), which enhances the clock signal distribution across the module. This is crucial for maintaining system stability and performance, particularly in high-frequency memory operations.

Signal Integrity

The CKD serves as a buffer for the clock signals sent from the CPU to the memory module. It reconditions both the timing and voltage amplitude of these signals, enhancing signal integrity by reducing clock jitter and ensuring synchronized timing across each memory chip. This is especially critical for high-speed memory, where even minor timing issues can cause errors or system instability.

Fig. 1: Clock topology in UDIMM

Fig. 2: Clock topology in CUDIMM

Fig. 3: A basic representation of how CKD works.

Fig. 4: Simulation of UDIMM at 8.4GT/s (CA bus and Clocks at DRAM locations) – Lowest clock amplitude is ~200mV differential.

Fig. 5: Simulation of CUDIMM at 10.0GT/s (CA bus and Clocks at DRAM locations) – Lowest clock amplitude is ~500mV differential with CKD.

Fig. 6: Simulation of CUDIMM at 11.6GT/s (CA bus and Clocks at DRAM locations) – Lowest clock amplitude is ~250mV differential with CKD.

Note: CA bus eye diagrams at different DRAM locations - Simulation results at 11.6MT/s (after additional tuning).

In CUDIMMs, clock signals are no longer the bottleneck in achieving higher frequencies. However, as the signals on the CA (Command and Address) bus are not buffered, our simulation indicate that the CA bus could eventually become a bottleneck for CUDIMMs. To address this, additional tuning is necessary to match the demands of extremely high DRAM speeds. At CORSAIR, innovation remains at the forefront as we strive to deliver the highest-frequency memory modules with unmatched reliability.

Clock Signal Synchronization

As DDR5 memory operates at increasingly higher frequencies, ensuring that all memory chips receive synchronized and stable clock signals, it becomes more challenging. The CKD buffers and re-distributes the clock signal, ensuring each chip on the module gets the same precise timing information. This leads to better signal integrity and minimizes clock jitter, which is crucial for high-speed data transfers and overclocking.

Support for Overclocking

With the support of the CKD, CORSAIR CUDIMMs are optimized for overclocking. These modules can handle higher voltages and speeds while maintaining signal quality, making them attractive for enthusiasts to push their systems to the limit.

Fig. 7: Screen shot of CORSAIR CUDIMM running at 9,600MT/s on the newly launched Intel® Z890 platform.

CKDs can operate in different modes such as Single PLL mode and Bypass mode.

Bypass mode - the CKD doesn’t regenerate and amplify the signal; basically, it works as a traditional UDIMM. This is used for compatibility on older DDR5 platforms. However, speeds may be limited to 6,000MT/s.
Single or Dual PLL mode - the user gets all the advantages of the CKD that are explained above. Currently this is only supported by the latest Intel® Z890 platform.

As of now, CUDIMMs are fully compatible with Intel platforms. AMD doesn’t support the Single or Dual PLL modes yet. Although if you plug a CUDIMM into an AMD platform, they tolerate the use of it by operating in Bypass mode only.