Today I want to share a rather niche and fairly ridiculous DIY mini PC build. The purpose of this design is to push the volume of a SFF PC with a discrete GPU below 1 liter, and to keep pushing it even further. Can you imagine that it is close to the size of a smartphone?
The main character is an obscure Fujitsu STX motherboard. Although it came from a prebuilt/business machine, it is indeed an STX-format board. As someone who jokingly considers himself an “STX expert,” I decided to use it for an ultimate just-for-fun mini PC project.
The final volume of the whole system is about 0.799L, just under 0.8 liters. The assembly photos were taken as screenshots from my video, so they may not be perfectly clear.
1. Core Specifications
The CPU on this motherboard is socketed and replaceable. For this build, I used:- CPU: Intel Core i7-11700T, 11th-gen low-power desktop CPU
- Motherboard: Fujitsu ESPRIMO G5011 STX motherboard, H510 platform
- GPU: SPARKLE RTX 4070M single-slot low-profile graphics card（using laptop chip for a desktop card）
- RAM: 2x8GB DDR4-2666 SO-DIMM
- SSD: HP 500GB NVMe SSD
- Power supply: 12V DC 180W or higher
- Case: a self-designed case made from 1 mm carbon fiber.
To keep full desktop-level expandability in the smallest possible volume.
2. Motherboard Modifications: Cutting Everything That Gets in the Way
To push the volume to the limit, I made quite a few aggressive modifications to this motherboard.2.1. Relocating the SSD
The original M.2 port is for M.2-to-PCIE riser now. The original Wi-Fi module position has been repurposed as the SSD mounting position, using a M.2 wifi to M.2 NVME adapter, can provide PCIE 3.0 x1 for SSD. The speed is somewhat reduced, but there is no noticeable impact in actual use.Wi-Fi will be handled later by an external USB Wi-Fi dongle. This frees up precious internal space for more important components. After all, in a sub-0.8L system, every single millimeter matters.
2.2. Laying the CMOS Battery Flat
The original CMOS battery was mounted vertically, which took up too much height.I converted it to a socketed setup, laid it flat, and secured it with silicone rubber. This helps further reduce the overall system height.
2.3. Synchronized Power-On Cable
I also made a synchronized power-on cable, so the GPU side can power on together with the host system. This avoids the issue of the external GPU power and the main system powering on at different times.
2.4. TPM Header Modification
There is a row of external TPM header pins on the motherboard. This build does not need them, and they also interfere with the available space.So I simply bent the pins down to avoid conflicts with the case, cooler, and other parts.
2.5. Adding VRM Cooling
The VRM on this board is a two-phase 45A design. The current capacity itself is actually enough, and the default current limit is 66A.The real problem is not current delivery, but heat dissipation.
So I added heatsinks to the VRM area, and also added thermal pad on the back side to conduct heat into the carbon fiber shell for additional cooling. This should help keep the power delivery section under control after unlocking the CPU power limit.
2.6. About the SATA Adapter Slot
There is a 2.5-inch adapter slot on the motherboard that looks a bit like a PCIe slot.However, on this H510 version of the board, this slot does not have PCIe lanes routed to it. It only carries SATA. The previous Q470 version of the board could use this position to break out a second M.2 slot, but this H510 version cannot.
If needed in the future, I could still solder wires from this position and connect a SATA drive.
8. Removing the LAN Port and Some USB Ports
The wired LAN port was too tall and would seriously affect the total system height, so I removed it directly.Originally, there were two groups of USB ports on the top, two on each side, four in total. I also removed two top USB, leaving the final layout as:
- 3 rear USB-A ports
- 2 USB-C ports
- 1 top USB port on each side
For this kind of just-for-fun mini PC, I think that level of expandability is basically enough.
3. Cooler and GPU Installation
The original CPU cooler is a very small blower-style cooler, made by Cooler Master.
I slightly sanded the cooler and raised it a bit, so there is enough clearance underneath for the SSD and the VRM cooling structure.
For the GPU, I used a SPARKLE RTX 4070M single-slot low-profile card. It is a pretty insane little thing. Only 151mm long.
To further reduce thickness, I removed the GPU shroud as well. This allows the graphics card to sit directly against the chassis, saving around 1mm of thickness.
In a build this small, even 1mm is a victory.
Before install the GPU, should install ADT M.2 to PCIE riser first.
Then install GPU.
Then finish the install.
4. First Power-On: No Smoke, Successful Boot
After everything was assembled, the first power-on was honestly a bit nerve-racking.Fortunately, there was no smoke, and the display came on successfully.
This machine was originally designed for 19V input, but I used a 12V power supply, so it reported two low-voltage errors on boot. I managed to get the boardview file for this motherboard and checked the circuitry, which showed that it can run perfectly fine on 12 V. Also the system runs normally in practice, so these warnings can be ignored .
5. Performance Testing
I modified some hidden BIOS options and unlocked the power limit to around 65W. This required a tool called RU, and the BIOS file also had to be parsed first to figure out which value needed to be changed.
CPU Benchmark
Cinebench R23 score:Around 9400 points
This is basically what you would expect from an 11th-gen low-power desktop CPU. It is not amazing, but considering the size of the machine, it is acceptable.
Time Spy GPU score:
Around 9200 points
This is mainly carried by the RTX 4070M. Since the GPU is running through PCIe 3.0 x4 from the H510 platform, there is some performance loss. I estimate the overall loss to be around 10%.
6. Game Testing
Forza Horizon 6
Benchmark : 85 FPSAt 1080P, using a recommended graphics preset found on internet, with frame generation disabled.
In-game, it can basically stay above 85 FPS, and when driving around in the open world, it often exceeds 100 FPS.
For a mini PC of this size, this is already a very enjoyable experience.
Black Myth: Wukong
Benchmark : 67 FPSSettings:
- Resolution: 1080P
- Super Resolution: 60
- Graphics Quality: High
- Frame Generation: Off
CS2
At 1080P low settings:- Average FPS: around 329 FPS
- Low FPS: around 110 FPS
In actual Dust II deathmatch gameplay, it usually runs at around 200 FPS. The low FPS is a bit on the lower side, but the overall experience is still fine.
7. Stress Testing and Temperatures
The question many people will definitely ask is:Can such a tiny system actually handle the heat?
So I ran a fairly brutal combined stress test.
On the GPU side, software reported around 87W. However, since this is a modded laptop GPU, the power reading may not be accurate. I estimate the actual power draw to be around 70W.
On the CPU side, power stabilized at around 59W.
For the CPU, I used a CPU-only stress test. If I run FPU, it hits the current limit first, and the power draw actually becomes lower, so it does not fully represent a realistic high-load scenario.
Temperature results:
- CPU: around 82°C
- GPU: around 67°C
- GPU hotspot: around 72–73°C
The GPU still has a decent amount of thermal headroom.
8. Noise: The Biggest Problem Is the GPU Fan
The biggest issue with this modded RTX 4070M is that it does not support PWM fan control.Also, single-slot low-profile cards like this are often installed in all kinds of terrible, cramped cases, so the manufacturer set the fan speed very high.
The result is simple:
Even at idle, it is quite noisy.
Measured noise levels:
- At about 10cm from the machine: around 71dB
- At a normal 50cm user distance: around 52dB
However, judging from the temperatures, the GPU has plenty of thermal headroom. Later, I plan to add a fan speed reduction cable to directly limit the fan speed, which should improve the noise level significantly.
9. Conclusion
At its core, this machine is an extreme-volume just-for-fun mini PC.I measured its dimensions.
The calculated result is 0.799 L. It was 0.79 L in the design drawing, but the seams need to be added after assembly.
In less than 0.8L of volume, it manages to fit:
- An STX motherboard with a replaceable CPU
- Intel Core i7-11700T
- RTX 4070M graphics card, while still retaining future GPU upgrade potential
- Replaceable memory and SSD
The biggest issue right now is the GPU fan noise, which I plan to improve later with a speed reduction cable.
Overall, this machine may not be practical, and it is definitely not for everyone. But as an extreme 0.799L DIY mini PC, I think it is genuinely interesting.
*In fact, I also got Fujitsu’s newer LGA1700-platform mini PC G6014, which can support up to 14th-gen CPUs, so of course its performance is much stronger. Unfortunately, the newer motherboard is 1.5 cm longer than STX, so this most extreme compact build can only be done with the 11th-gen platform.
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