内容来源：https://www.engadget.com/2257761/egpu-come-with-limitations/

内容总结：

外接显卡可用但限制明显，直接购买入门游戏主机或许更划算。在内存价格高企的背景下，外接显卡成为笔记本用户提升游戏性能的替代方案。外接显卡通常由桌面级显卡加拓展坞组成，通过雷雳或USB4连接笔记本或掌机，能接管渲染任务，让轻薄设备运行大型游戏，但存在诸多限制。雷雳接口下外接显卡性能通常低于桌面内置，拓展坞本身售价数百美元，苹果Silicon Mac完全无法用于游戏。不过外接显卡生态正迎来复苏，雷蛇于2025年7月推出雷雳5拓展坞，Framework也在为Laptop 16开发外接显卡套件。

性能损耗方面，雷雳4接口总带宽40Gbps，其中PCIe数据仅占32Gbps，约为桌面PCIe 4.0 x16插槽的八分之一。纹理和着色器载入显存后无需重复传输，但游戏加载新资源或回传画面时带宽压力明显。Notebookcheck在2021年测试RTX 2080 Ti外接方案，性能损失在7%至32%之间；4K外接显示器时损失降至个位数，但渲染回笔记本屏幕时因画面需回传而更慢。PC Gamer测试显示，RTX 4070 Ti在雷雳下比OCuLink慢约25%，1%低帧更差且卡顿更多；从4070 Ti升级到4090时，雷雳和OCuLink下的增益远小于桌面平台。显卡越快，雷雳带宽瓶颈越明显，中端显卡更适合外接方案。雷雳5提供80Gbps带宽，雷蛇Core X V2售价350美元，通过PCIe 4.0 x4连接显卡，标称64Gbps，相当于x16显卡只获得4条通道。

成本与兼容性方面，Core X V2仅含拓展坞，不含电源、USB接口和网口，需自备ATX电源，雷蛇另售雷雳5拓展坞起价390美元。加上显卡本身，总花费已接近一台入门游戏主机，且后者无带宽瓶颈。雷雳5笔记本目前仅限于高端游戏本和移动工作站，连接雷雳4笔记本时带宽仍限制在40Gbps。OCuLink通过线缆直传PCIe绕过雷雳，Framework采用此方案，其Laptop 16开发套件提供八通道PCIe，速率最高128Gbps，但OCuLink不供电、不支持即插即用，便利性打折扣。苹果自2020年转向自研芯片后已放弃外接显卡支持，macOS至今未恢复图形加速功能。今年苹果批准了tinygrad项目的TinyGPU驱动扩展，可在雷雳或USB4下驱动较新AMD和Nvidia显卡，但仅限AI负载，无显示输出，无法用于游戏。

中文翻译：

eGPU确实能用，但也有一些明显的局限。
不如直接买一台入门级游戏PC。
如果你一直想给笔记本提升游戏性能，又不想在内存价格暴涨的当下花钱换新机，外置显卡（eGPU）可能是你最好的选择。eGPU就是外置图形处理器，通常是把一块台式机显卡装进扩展坞里，通过雷电或USB4接口连接到兼容的笔记本或游戏掌机上。它在接管渲染方面表现相当不错，意味着即便是更轻薄、性能更弱的机器，接上eGPU也能运行要求更高的游戏，但需要注意的问题也不少。
一块显卡以外置方式运行，通过雷电接口的速度通常会比装在台式机里慢。容纳显卡的扩展坞本身也要花上好几百美元，而且有些设备，比如搭载Apple Silicon的Mac，根本不能用eGPU来玩游戏。话虽如此，eGPU硬件如今的状况比过去几年都要好。雷蛇在2025年7月推出了Thunderbolt 5扩展坞，重启了其eGPU产品线，Framework也在为其Laptop 16打造eGPU套件。
eGPU会损失多少性能？
一个Thunderbolt 4接口的带宽为40Gbps，英特尔的规范将其中32Gbps分配给PCIe数据传输，这只是桌面PCIe 4.0 x16插槽带宽的八分之一。eGPU扩展坞中显卡的大部分工作数据根本不会经过雷电线缆。纹理和着色器只需加载到显存中一次，之后便一直留在那里，也就是说，只有当游戏加载新资源或将渲染完成的画面传回显示器时，线缆才会忙碌起来。
笔记本评测网站Notebookcheck在2021年测试了一款RTX 2080 Ti扩展坞，发现与台式机相比性能损失在7%到32%之间。在外接显示器上以4K分辨率运行时，损失确实缩小到了个位数百分比，但渲染到笔记本屏幕上会更慢，因为完成的画面要沿着同一根线缆传回来。相比之下，PC Gamer测试了RTX 4070 Ti和4090在雷电、OCuLink和桌面PCIe下的表现。在许多1440p测试中，其RTX 4070 Ti通过雷电运行比通过OCuLink慢了约25%，1%最低帧更低，卡顿也更多。
PC Gamer还指出，从4070 Ti升级到4090时，通过雷电和OCuLink获得的性能提升比台式机更小。所以，显卡越快，雷电线缆对其性能的限制就越大，这使得中端GPU成为eGPU扩展坞更明智的选择。Thunderbolt 5提供80Gbps的连接带宽，而雷蛇售价350美元的Core X V2通过PCIe 4.0 x4连接GPU，标称带宽64Gbps。这意味着x16显卡只能获得四条通道，而非合适桌面插槽中的十六条。
成本与兼容性
Core X V2只包含扩展坞本体，不含电源、USB接口或以太网口。你需要自己加装ATX电源，而雷蛇现在将缺失的I/O接口作为Thunderbolt 5扩展坞单独出售，Mercury版本起价390美元。再加上显卡本身的费用，与其买齐这些组件，还真不如直接入手一台入门级游戏主机。至少这样你就避开了外接连接的带宽限制。除了高端游戏本和移动工作站之外，搭载Thunderbolt 5的笔记本也屈指可数，所以把扩展坞连接到兼容的Thunderbolt 4笔记本时，连接带宽无论如何都被限制在40Gbps。
OCuLink倒是绕过了雷电的限制，直接通过线缆传输裸PCIe信号。这正是Framework采用的方案。其OCuLink开发套件在Laptop 16上提供八通道PCIe连接，速率高达128Gbps。但这样一来你就牺牲了一些便利性，因为OCuLink不为宿主设备供电，也没有雷电扩展坞那种单线连接的即插即用体验。
苹果在2020年转向自研芯片时放弃了对eGPU的支持。此后没有任何macOS版本恢复对图形加速的支持。不过，苹果今年早些时候批准了TinyGPU，这是tinygrad项目的一个驱动扩展，可以通过雷电或USB4运行较新的AMD和Nvidia显卡。但它仅用于AI工作负载，而且没有显示输出，意味着在游戏场景下派不上任何用场。

英文来源：

eGPUs do work, but they come with some notable limitations
Just buy a basic gaming PC instead.
If you've been looking to get more gaming power out of your laptop but don't want to pay for a replacement amid RAMpocalypse pricing, an eGPU could be your best bet. An eGPU is an external graphics processor, usually a desktop graphics card in an enclosure connected to a compatible laptop or gaming handheld through Thunderbolt or USB4. They can be pretty good at taking over rendering, meaning even thinner and weaker machines can run more demanding games with one plugged in, but there are many caveats.
A GPU run as an eGPU will typically operate slower over Thunderbolt than it would inside a desktop. The enclosure to house it costs hundreds of dollars too, and some devices, like Apple Silicon-based Macs, can't use an eGPU for gaming at all. That said, eGPU hardware is in better shape today than it has been in years. Razer revived its eGPU line with a Thunderbolt 5 dock in July 2025, and Framework is building an eGPU kit for its Laptop 16.
How much performance is lost with an eGPU?
A Thunderbolt 4 port carries 40Gbps, and Intel's spec allots PCIe data 32 Gbps of it, an eighth of the bandwidth a desktop PCIe 4.0 x16 slot provides. Most of what the card in an eGPU enclosure does will never cross the Thunderbolt cable. Textures and shaders get loaded into VRAM once and remain there, meaning the cable only gets busy when a game pulls in new assets or sends finished frames back to the display.
Portables review site Notebookcheck tested an RTX 2080 Ti enclosure back in 2021 and found deficits ranging from seven to 32 percent when compared to a desktop. Losses did shrink to single digits at 4K on an external monitor, but rendering to a laptop is slower because finished frames travel back down the same cable. In contrast, PC Gamer tested an RTX 4070 Ti and 4090 over Thunderbolt, OCuLink and desktop PCIe. Its RTX 4070 Ti ran around 25 percent slower over Thunderbolt than OCuLink in many 1440p tests, with lower 1 percent lows and more stuttering.
PC Gamer also claimed that upgrading from the 4070 Ti to the 4090 delivered smaller gains over Thunderbolt and OCuLink compared to desktop. So, the faster the card, the more of its performance the Thunderbolt cable restricts, making a mid-range GPU the more sensible choice for an eGPU enclosure. Thunderbolt 5 provides 80 Gbps of connection bandwidth, while Razer's $350 Core X V2 connects the GPU through PCIe 4.0 x4, nominally 64 Gbps. That gives an x16 graphics card four lanes instead of the 16 available in a suitable desktop slot.
Cost and compatibility
The Core X V2 comes with only the enclosure; no power supply, USB ports or Ethernet. You'll need to add your own ATX PSU, and Razer now sells the missing I/O separately as a Thunderbolt 5 dock starting at $390 for the Mercury version. Throw in the graphics card itself and there's really little point in buying all these components when you could just invest in a budget gaming rig instead. At least in doing so, you'll be avoiding the external connection's bandwidth limit. Thunderbolt 5 laptops are also few and far between outside premium gaming machines and mobile workstations, so connecting the enclosure to a compatible Thunderbolt 4 laptop limits the connection to 40 Gbps regardless.
OCuLink does manage to get around Thunderbolt by running bare PCIe over a cable. That's the route Framework is taking. Its OCuLink Dev Kit exposes an eight-lane PCIe connection on the Laptop 16, rated at up to 128 Gbps. You end up sacrificing some convenience here given that OCuLink doesn't power the host, and there's none of the plug-and-play that makes a Thunderbolt box a one-cable dock.
Apple dropped eGPU support with its move away from Intel silicon back in 2020. No macOS release since has brought it back for graphics acceleration. However, Apple did approve TinyGPU earlier this year, a driver extension from the tinygrad project that runs newer AMD and Nvidia cards over Thunderbolt or USB4. It's for AI workloads only, and its lack of display output means it won't get you anywhere for gaming use cases.