From HPC to AI: How Compute Express Link (CXL) is Transforming Computing Performance

From HPC to AI: How Compute Express Link (CXL) is Transforming Computing Performance

Compute Express Link (CXL) is an open standard for high-speed, low-latency interconnects between processors and devices, such as accelerators and memory. It is designed to enhance the performance of data centres by improving the communication between CPUs and other components like GPUs, FPGAs, and memory devices. CXL aims to provide a unified interface for data communication, reducing complexity and improving efficiency.

Key Features and Specifications of CXL

  • High Bandwidth and Low Latency: CXL provides a high-bandwidth, low-latency connection, which is essential for high-performance computing (HPC) and data-intensive applications.
  • Memory Coherency: It ensures memory coherency between the CPU and connected devices, allowing shared memory space and reducing the overhead of data movement and synchronization.
  • Three Protocols in One:
    • Based on PCI Express (PCIe) 5.0, it handles I/O traffic.
    • CXL.cache: Allows memory sharing and coherence between the CPU and device caches.
    • CXL.memory: Enables direct memory access and pooling, enhancing memory utilization and efficiency.
  • Backward Compatibility: CXL is backward compatible with PCIe, allowing existing infrastructure to support CXL devices without significant changes.
  • Flexibility: CXL supports various usage models, including memory expansion, accelerator integration, and resource pooling.
  • Device types: CXL is designed to support three primary device types.
    • Type 1 ( and CXL.cache): Specialized accelerators (like smart NICs) without local memory, relying on coherent access to the host CPU’s memory.
    • Type 2 (, CXL.cache, and CXL.mem): General-purpose accelerators (GPU, ASIC, or FPGA) equipped with high-performance GDDR or HBM local memory. These devices can access the host CPU’s memory coherently and provide either coherent or non-coherent access to their local memory from the host CPU.
    • Type 3 ( and CXL.mem): Memory expansion boards and persistent memory devices that offer the host CPU low-latency access to local DRAM or byte-addressable non-volatile storage.
VersionRelease DateKey Features
CXL Spec 1.0March 11, 2019Allows host CPU to access shared memory on accelerator devices with a cache coherent protocol.
CXL Spec 1.1June, 2019Follow-up version to 1.0 with likely minor improvements and bug fixes.
CXL Spec 2.0November 10, 2020Adds support for CXL switching, enabling connections of multiple CXL 1.x and 2.0 devices to a CXL 2.0 host processor. Introduces distributed shared memory and disaggregated storage configurations. Implements device integrity and data encryption. Utilizes PCIe 5.0 PHY without bandwidth increase from CXL 1.x.
CXL Spec 3.0August 2, 2022Based on PCIe 6.0 physical interface with PAM-4 coding, doubling bandwidth. Introduces fabric capabilities with multi-level switching and support for multiple device types per port. Enhances coherency with peer-to-peer DMA and memory sharing.

Uses of CXL

  • Accelerator Integration: CXL is used to connect CPUs with accelerators such as GPUs, FPGAs, and AI processors. This is crucial for applications in machine learning, artificial intelligence, and data analytics, where offloading tasks to specialized hardware accelerators can significantly boost performance.
  • Memory Expansion and Pooling: CXL allows for memory expansion beyond what is physically available on the CPU. It enables the use of high-capacity memory devices, improving performance for memory-intensive applications. Memory pooling allows multiple processors to share a common memory pool, increasing efficiency and flexibility in resource allocation.
  • High-Performance Computing (HPC): In HPC environments, CXL’s low-latency, high-bandwidth interconnect improves data transfer rates and efficiency, essential for scientific simulations, large-scale data analysis, and other compute-intensive tasks.
  • Data Centres: CXL can enhance data centre performance by enabling more efficient use of resources, reducing latency, and improving overall system throughput. This is particularly beneficial in hyperscale data centres where performance and efficiency are critical.
  • Cloud Computing: In cloud environments, CXL supports dynamic resource allocation, allowing cloud providers to offer scalable and efficient services. It enables better utilization of hardware resources, reducing costs and improving performance for end-users.

Choosing Between CXL and PCIe: Which Interconnect is Right for Your Application?

Compute Express Link (CXL) and PCI (Peripheral Component Interconnect) / PCIe (PCI Express) are both standards used for interconnecting computer components, but they serve different purposes and have distinct features:

Compute Express Link (CXL):

  • Focused on Accelerators and Memory: CXL is designed specifically to address the needs of connecting accelerators and memory (both DRAM and persistent memory) to CPUs.
  • Memory Coherency: CXL supports memory coherency between the CPU and connected devices, allowing shared memory address spaces and efficient data movement.
  • Unified Protocol: CXL combines elements of PCIe for I/O with additional protocols for memory and cache coherency, offering a unified approach to connectivity and memory management.
  • Enhanced Bandwidth and Efficiency: CXL aims to provide higher bandwidth and lower latency compared to traditional PCIe, making it suitable for high-performance computing, AI, and data-intensive applications.
  • Industry Support: CXL is supported by a consortium of major technology companies, including Intel, AMD, NVIDIA, and others, indicating strong industry backing.


  • Legacy and Broad Adoption: PCI has been a longstanding standard for connecting peripheral devices to a computer’s motherboard. PCIe is the modern iteration of PCI, offering higher bandwidth and faster data transfer rates.
  • Peripheral Connectivity: PCIe is primarily used for connecting peripherals such as graphics cards, network cards, storage devices (like SSDs), and other expansion cards to the CPU and motherboard.
  • Point-to-Point: PCIe operates as a point-to-point connection between a device and the CPU/memory controller, with each device having its own dedicated bandwidth.
  • Multiple Versions: PCIe has evolved over several generations (PCIe 1.0 to PCIe 5.0 as of the latest standards), each increasing bandwidth and data rates significantly.
  • Backward Compatibility: PCIe standards are backward compatible, meaning newer devices can generally work with older PCIe slots, albeit at reduced speeds.

Key Differences:

  • Purpose: PCIe is for general-purpose peripheral connectivity, while CXL is optimized for connecting accelerators and memory to CPUs.
  • Protocols: PCIe is primarily focused on I/O traffic, whereas CXL integrates memory and cache coherence protocols alongside I/O.
  • Bandwidth and Efficiency: CXL aims for higher bandwidth and lower latency, critical for modern data-intensive applications compared to PCIe.
  • Target Applications: PCIe is used broadly across all computing domains, while CXL is particularly advantageous in HPC, AI, and data center environments where accelerating data movement and computation are paramount.

In essence, while both PCI/PCIe and CXL serve as interconnect standards, CXL specifically targets the needs of modern computing architectures that require high-speed, low-latency connections between CPUs and specialized accelerators and memory devices.

From HPC to AI: How Compute Express Link (CXL) is Transforming Computing Performance

Industry Adoption

CXL is supported by a consortium of major industry players, including Intel, AMD, NVIDIA, Microsoft, and many others. Its adoption is growing as data centres and enterprise computing systems seek to leverage its advantages for improved performance, scalability, and efficiency.



As you’ve discovered, Compute Express Link (CXL) stands at the forefront of technological advancement, revolutionizing industries and applications across the board. From enhancing high-performance computing and AI to optimizing data centres and accelerating breakthroughs in research, CXL offers unparalleled speed, efficiency, and scalability.

Contact BVM for Your Industrial and Embedded Computing Needs

Ready to integrate CXL into your infrastructure or looking for specialized hardware solutions? Contact us (BVM) today for all your Industrial and Embedded Computing needs. With over 35 years of experience, we specialize in providing tailored solutions to meet your specific requirements.

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