As we’ve gained a better understanding of Thunderbolt 3 (TB3) eGPU enclosures, the unknown rests on the performance of the Thunderbolt 3 host computer. Thin and light ultrabooks are often a top choice to pair with an external GPU. This article serves as a buyer’s guide for choosing the best ultrabook to get the most out of a TB3 eGPU. The particular setup I’m using is an early 2018 Razer Blade Stealth with the Razer Core V2. This pairing is one of the highest performing TB3 ultrabook + eGPU setups as of Q1 2018. The Razer Blade Stealth shares many fundamental components with a handful of other Thunderbolt 3 ultrabooks that we will explore below.
Intel Thunderbolt Technology website has a list of certified Thunderbolt products. You can visit this link to find Thunderbolt 3 laptops currently available on the market. The multitude of choices can be overwhelming. Yet the specifications we’re most interested in for external graphics use are not readily available. So what are the criteria you should consider when choosing the best ultrabook for external graphics pairing? Through hundreds of implementations and build guides, we’ve distinguished three key features:
For this buyer’s guide, we’re focusing on the newest crop of ultrabooks with Thunderbolt 3 connectivity. They now sport the Intel 8th generation quad-core ULV processors, doubling the core count of the previous generation. The top turbo speed is dependent on both the CPU workload and the ultrabook’s cooling system. If nearing the limits of TDP and CPU junction temperature (95˚-105˚ C), the CPU will throttle down performance. Thin, light systems are more than skin deep.
With nearly identical architecture to the previous generation, the 8th generation ULV CPU offers performance improvements by running double the number of cores, often at a more efficient reduced speed to maintain limits and thereby giving greater overall workload. These ultrabooks are the first revision with quad-core processors and should be future-proof for the next few years. At this time, the i7-8550U configuration was the highest performing, readily available ULV CPU.
|Spec||Intel Core i7-8550U @ 1.80GHz||Intel Core i7-7600U @ 2.80GHz|
|Base Speed||1.8 GHz||2.8 GHz|
|Turbo Speed||Up to 4.0 GHz||Up to 3.9 GHz|
|# of Physical Cores||4 (2 logical cores per physical)||2 (2 logical cores per physical)|
|First Seen on Chart||Q2 2017||Q1 2017|
|Single Thread Rating||2079||2128|
|CPU Mark (Feb-2018)||8111||5583|
Thunderbolt connection allows at most 4 PCI Express lanes between the host and the device. In a ULV CPU ultrabook, this means allocating 4 out of a maximum 12 PCIe lanes. There are several peripheral components inside a laptop that make use of these high-speed interconnect lanes. For a typical ultrabook the NVMe flash storage drive gets a x4 PCIe connection. The Wireless card and other components may use a few x1 PCIe connections. If there’s a discrete graphics card, it will consume another x4 PCIe connection. Resource allocation conflicts arise when PC manufacturers decide how best to use these 12 lanes. Due to Thunderbolt 3 connectivity being a relatively new standard, Thunderbolt 3 ports are often not top priority.
One performance hindrance is a x2 PCIe 3.0 via Thunderbolt 3 connection. This is applicable for most single TB3-port ultrabooks, the Razer Blade Stealth being the exception. The Dell XPS 13 is perhaps one of the most popular ultrabooks in the past few years. Many aim to use it with an eGPU, but it’s been plagued with only 2 lanes for its sole Thunderbolt 3 port. The good news is things are gradually changing with the emergence of Thunderbolt 3 external graphics solutions. At CES 2018 I had a discussion regarding this with Gary L., a Dell system engineer. He confirmed the latest 2018 XPS 13 9370 now provides 4 PCIe lanes for its dual Thunderbolt 3 ports.
The HWiNFO64 screen capture on the left shows PCIe configuration in the early 2018 Razer Blade Stealth. The PCI Express Root Port #5 [A1/C1] attaches to a x4 connection that connects to the Thunderbolt 3 [Alpine Ridge] controller. This controller then hosts a single Thunderbolt 3 port. We also see PCI Express Root Port #3 [A1/C1] attaches to the Killer Wireless-n/a/ac 1535 Network Adapter. Last but not least, PCI Express Root Port #9 [A1/C1] attaches to a Samsung NVMe 960 controller. The HWiNFO64 screen capture (on the right) of a Dell XPS 9360 shows its inferior x2 PCIe connection to the Thunderbolt 3 controller.
An infrequently discussed feature is the On Package DMI interconnect Interface (OPI). ULV processors such as the i7-8550U use OPI because, unlike HQ or HK processors, it lacks the Direct Media Interface (DMI 3.0) to facilitate communication between the PCH and CPU. The system designers can choose to either extract the most performance or optimize energy consumption on these ULV processors. OPI 2GT/s is ideal for extended mobile use at low-power tasks, while OPI 4GT/s is excellent for high-performance applications. These two OPI modes operate at a max theoretical throughput of 20Gbps and 40Gbps respectively. When you consider Intel’s claim of 40Gbps bandwidth for Thunderbolt 3 connectivity, it makes total sense OPI 4GT/s is the more appropriate choice for eGPU use.
Unfortunately the OPI settings are not something users can change at their convenience. The settings are baked into the system firmware/BIOS. At the moment PC manufacturers do not disclose the OPI mode in their marketing information. The only way to find out is to run performance tests yourself. If the ultrabook has an NVMe storage controller, read speed should exceed 1,800 MB/s in benchmark software such as ATTO to confirm the laptop is set to OPI 4GT/s.
As seen in the AIDA64 benchmarks above, OPI 4GT/s systems can extract the most out of Thunderbolt 3 eGPU. Keep in mind that Intel caps the throughput in these eGPU enclosures at roughly 22Gbps to preserve bandwidth for DisplayPort transmission over Thunderbolt 3. As external graphics adoption and demand grows, we hope Intel and partners dedicate more resources to optimize Thunderbolt 3 performance in general and external graphics use in specific.
Below are the best ultrabooks with the trinity of performance specs to host an external GPU. If you have an Intel 8th gen quad-core ultrabook not in this list and can confirm x4 PCIe + OPI 4GT/s, please share your findings by posting a build guide in our forum. We’ll keep this list up-to-date with user reports.
Dell XPS 13 9370
$1,399i7 Starting MSRPCheck current price
HP Spectre X360 13t
$1,099i7 Starting MSRPCheck current price
Lenovo Yoga 920
$1,299i7 Starting MSRPCheck current price
Razer Blade Stealth Featured in article
$1,449i7 Starting MSRPCheck current price
Want more performance?
The rumor mill suggests that Intel will release 8th-generation 6-core (hex) Q 45W CPUs. These will be in laptops with larger chassis to accommodate more substantial cooling systems, coupled with bulkier power supplies to drive them. A bigger package that packs a bigger punch. It’s definitely worth the wait if you can trade portability for performance.
Older notebook options?
eGPU.io user builds listed as 32Gbps-TB3 are confirmed to offer full Thunderbolt 3 bandwidth performance. At the link below, you can select LCD, CPU and then review the System Brand and Model widget for options to consider. Proceed to review user builds with your targeted system.
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