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Exploring PCIe Expansion Technology:
What External PCIe Expansion Solutions are available in today’s marketplace?
In today's fast-paced technical landscape, expanding the capabilities of your workstations and servers is no longer a luxury—it's a necessity. For demanding AI and High-Performance Computing (HPC), applications, and professional content creation workflows, an external PCIe expansion solution can be the key to unlocking maximum performance without having to replace your entire platform. Determining the best match for your target application and platform, however, depends entirely on your bandwidth, scalability, and form factor requirements.
This article seeks to weigh the pros and cons of the preeminent expansion technologies, and explores the leading expansion solutions available for each interface.
Thunderbolt and USB4: The Default Choice for Desktops & Consumer Grade Applications
For laptops, small-form-factor desktops, or compact workstations that need to add one or two PCIe devices, Thunderbolt and USB3/4 based solutions remain the most common and convenient options. Both interfaces leverage USB-C connector to tunnel PCIe signals, and are ideal for consumer-grade applications, including backup storage and on-the-fly device expansion for a laptop or notebook.
Thunderbolt 3 & 4, with a bidirectional bandwidth of up to 40 Gbps (equivalent to a PCIe 3.0 x4 link), is a solid option if you are looking to add a single eGPU for a quick video editing project, a high-speed NVMe drive, or a professional video capture card.
Shown above: HighPoint RocketStor 6661B Thunderbolt to PCIe Expansion Chassis
The newest iteration of the technology, Thunderbolt 5, pushes this further, offering the equivalent of a single Gen4 x4 connection with up to 80 Gbps bidirectional (and even 120 Gbps for display-focused workloads). This makes it a more viable solution for multi-display setups and more demanding applications. However, Thunderbolt 5’s is still relatively new to the marketplace, and is not yet widely available. In addition, Thunderbolt 5 capable devices are much harder to source over their TB3/4 counterparts.
USB 3/4 offers similar performance to Thunderbolt 3 & 4, with up to 40 Gbps. However, if you are considering USB connectivity for PCIe expansion, it's important to confirm that the target host system's USB port supports PCIe tunneling. Its broader compatibility across both Intel and AMD platforms makes it a flexible alternative for many, as just about any modern computing platform sports at least 1 USB 3 or 4 port, regardless of their intended application.
USB based solutions appeal to many users due to their portability, simple plug-and-play operability, and ability to power the hosted device – all of which can streamline a crowded workspace. They are a compelling choice for professionals that need to broaden connectivity options for a portable system, or are seeking a simple on-the-fly expansion solution for a space-constrained desktop or mini-PC environment.
However, if performance is your key consideration, Thunderbolt and USB solutions are not ideal. While plenty fast enough for day-to-day transactions, and some professional applications in a pinch, they place severe restrictions on modern storage media (NVMe in particular) and high-end PCIe devices, such as a Gen4/5 GPU. PCIe bandwidth generally tops out at x4 lanes, is limited to Gen3, and has to be distributed to all connected devices. To put this into perspective, a single off-the-shelf consumer M.2 SSD can easily saturate x4 lanes of bandwidth during a routine data transaction!
PCIe Switch Solutions: Dedicated Enterprise-Grade Performance for Uncompromising Professionals
For mission-critical applications in AI, HPC, and large-scale NVMe storage, where speed is paramount, consumer-grade connectivity solutions simply won't suffice. This is where a dedicated PCIe switch adapter and cabling solution can shine brightest. PCIe Switching architecture bypasses the inherent limitations of Thunderbolt and USB technology by providing a direct, uncompromised connection between the host platform’s CPU and your target expansion device.
A dedicated PCIe Switch Solution is generally comprise of a PCIe Switch Host Adapter, such as HighPoint’s PCIe Gen5 x16 Rocket 1628D, installed in the server/workstation chassis and linked to an external enclosure via a specialized, enterprise-grade cabling solution.
This architecture delivers a full x16 lanes of PCIe bus bandwidth, such as a dedicated Gen5 x16 link, which is capable of transmitting data at a staggering 60 GB/s with minimal latency! This level of sustained transfer speed is essential for data intensive applications including AI, ML, Scientific modeling and Engineering, and 3D design and animation workflows, all of which increasingly rely on high end GPUs and today’s fastest NVMe storage to maintain optimal performance.
High-end turnkey solutions, like those offered by HighPoint Technologies, employ state of the art PCIe Switch ICs, such as Broadcom 48-lane PEX 89048, and innovative CopprLink-CDFP cabling connectivity to deliver uninterrupted bandwidth and minimize latency between the hosted device and computing platform.
This type of solution, such as HighPoint’s innovative Rocket 7638D, allow for a massive 128 GB/s of bi-directional bandwidth, ensuring that multiple high-end GPUs or large arrays of NVMe SSDs can operate at their maximum potential, simultaneously! These robust solutions are designed for ease of use, with native support across major operating systems, providing enterprise-class performance and reliability without the traditional complexity. In addition, HighPoint’s flexible firmware architecture enables such solutions to be custom tailored for specific applications, enabling the Adapter to provide PCIe Bifurcation on the fly (PCIe lane allocation). This approach is the clear choice for the uncompromising professional and high-demand applications where absolute speed and scalability are the top priorities.
How to Choose the Right External PCIe Expansion Solution for AI, HPC and Content Creation
As performance demands increase across industries like AI, HPC, content creation, and edge computing, the need to scale compute and storage resources externally has become essential. Choosing the right external PCIe expansion solution depends on your application’s bandwidth requirements, system architecture, and performance expectations. Below, we break down the three major categories available today, along with their ideal use cases and limitations.
1. Thunderbolt-Based Expansion Chassis
Thunderbolt is a common connectivity solution for users that rely on laptops, compact desktops, or mobile edge computing systems. Thunderbolt leverages a USB-C connector to tunnel PCIe signals over a high-speed interface.
Key Specs:
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Thunderbolt 3/4: Up to 40Gbps (~PCIe 3.0 x4)
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Thunderbolt 5: Up to 80Gbps, and 120Gbps (for display-focused bursts)
Pros:
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Portability: Compact and lightweight enclosures make Thunderbolt ideal for mobile content creators or edge deployments.
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Power Delivery: Many Thunderbolt enclosures directly power the host device, reducing cable clutter
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Daisy-Chaining: Multiple devices or even enclosures can be connected through a single port (though bandwidth must be shared)
Cons:
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Bandwidth is capped at PCIe Gen3 x4 equivalent. Thunderbolt 5’s Gen4 x4 capability is a notable improvement, but can still only provide enough bandwidth for a single Gen4 NVMe SSD.
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Not ideal for data-heavy AI or HPC workloads due to protocol’s overhead and the potential of increased latency depending on device configuration.
2. USB4-Based Expansion Chassis
USB4 combines elements of USB and Thunderbolt technology. It offers broad compatibility with both AMD and ARM-based systems across Windows and Linux-based OS, making it a flexible option for mixed environments, as a single device can potentially be shared between multiple platforms.
Key Specs:
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Up to 40Gbps bandwidth with optional PCIe tunneling.
Pros:
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Cross-Platform Compatibility: Works across Windows, macOS, and Linux, regardless of CPU brand.
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Thunderbolt 3-Compatible: Many USB4 ports support legacy Thunderbolt devices.
Limitations:
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PCIe tunneling is not universally available, and performance may vary depending on the host platform’s USB controller.
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Significantly Lower bandwidth ceiling than dedicated PCIe solutions.
3. Dedicated PCIe Switch Adapter & Cabling Solutions
For applications that demand maximum sustained bandwidth, such as large-scale AI model training, 8K video editing, or real-time data processing in a HPC environment, only a direct PCIe Switch expansion solution is up to the task.
HighPoint’s Switch-based solutions—such as the RocketStor 8631CW Gen5 x16 eGPU Enclosure and RocketStor 654xAW Gen4 x16 NVMe Storage Enclosure, and revolutionary Rocket 7638D External PCIe Switch Adapter feature:
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Integrated 48-lane PEX series Broadcom PCIe Switches
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CopprLink™ and CDFP Connectivity, delivering a true Gen5 x16 connection (128GB/s bi-directional bandwidth)
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Up to 60GB/s sustained throughput
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Native driver support for Windows, Linux, and macOS
Ideal For:
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AI & Machine Learning: Training and inferencing large datasets
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HPC: Scientific simulations, genomic sequencing, and financial modeling
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Media Production: 8K+ video editing, VFX rendering, Game Development & Animation
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Edge Computing and Industrial Applications: High-throughput I/O with low-latency processing in a compact form factor
Benefits:
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Unmatched Performance: No tunneling, no overhead—just raw, maximized PCIe bandwidth without the latency
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Turnkey Simplicity: The bundled low-profile adapter, enterprise-grade cabling and external enclosure, and native hardware support make for true plug-and-play deployment.
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Scalability & Flexibility: Expand GPUs, NVMe storage, or accelerators effortlessly, on the fly as the need arises. Customizable firmware packages enable solution providers to craft unique products and appliances for a wide range of high-demand applications.
Conclusion: Matching the Right Expansion Solution to the Right Job
Solution Type | Ideal For | Max Bandwidth | Pros | Limitations |
Thunderbolt 3/4/5 | Mobile creators, small-scale edge use | 40–80Gbps | Portable, power delivery, daisy-chain | Limited to PCIe Gen3 x4, protocol overhead |
USB4 | Mixed-platform use, general workloads | 40Gbps | Broad compatibility | PCIe tunneling optional, lower ceiling |
PCIe Switch + Cabling (Gen5) | AI, HPC, 8K content creation, enterprise edge | Up to 128GB/s | Direct connection, no overhead | Requires x16 slot, higher initial cost |
When performance, reliability, and scalability are mission-critical, a dedicated PCIe Expansion solution is the clear choice. While Thunderbolt and USB4 are perfectly serviceable for lighter or portable workflows, PCIe Switch solutions stand in a league of their own. The Advantage of a Dedicated PCIe Switch Adapter & Cabling Enclosure are Clear; HighPoint Gen5 PCIe Switch GPU and Storage expansion solutions deliver the uncompromised speed, flexibility and enterprise reliability needed to tackle today’s most demanding AI, ML and Professional Media applications.