Antminer S21 Technical Deep Dive

Bitmain’s newest model, the Antminer S21 200TH, has been the number one ASIC on the market since its release in January 2024. But what is it? Braiins provides an in-depth look on it – from hardware, to firmware, and the most important thing – performance.

Executive summary

‍The Antminer S21 is a product that consumers waited nearly four years for. It has roughly twice the hashrate of the previous generation, the Antminer S19.

Below, we take a look at the hardware that drives this impressive computing power. Unpacking the miner, we see that multiple improvements on the prior generation have been made, while other components have remained the same.

Hardware - outside

Miners now can save time and money on cords, as the S21 finally comes with its own power cables. The rest of the miner, however, looks and weighs very similar to the S19:

• The machine has the standard Bitmain design – extruded body carrying three hashboards inside.
• Similarly, the Power Supply Unit has the same mechanical interface as before.
• The upper cap with the control board also remains the same.
• The “UI” of the outside hardware offers an Ethernet port, IP report button, reset button, 2-color LED semaphore, and a micro USB interface.

SUMMARY: Bitmain took the “If it ain’t broke, don’t fix it” methodology when designing the outside of this new generation, as everything has been seen on previous models. The inside is where we see some changes.

Hardware - inside

The inside of the S21 is where we see some changes from last generation to this one. What’s the same, and what’s different?

• Communication connectors linking the PSU and hashboard are the same.
• The control board is very similar, with the ATX 4 pin connector used
  • This supports the stronger fans on the S21 - this is a key differentiator of the S21, we all know heat can be an issue so better fans improve design.
• There are 324 total ASIC chips on the S21
  • There are fewer chips per domain, and the actual placement of the chips is different
    • Why does it matter? This provides a positive effect on heat dissipation and cooling – a common theme on the inside of this new model.
  • Each chip has its own temperature sensor, which is a massive upgrade from previous models
    • Previously, it was common to see just 2 or 4 sensors on each hashboard.
    • This change, again, is likely to improve on overheating issues and hardware failures of other S19 models.

SUMMARY: The hot new miner has some cool new features on the inside – temperature regulation is key for miners. That is now easier. With nearly 100% more computing power and nearly 15% more stock energy use than previous models, Bitmain ensured that the S21 will thrive in higher adiabatic temperatures.

Cooling

As discussed above, there was a strong emphasis on cooling in this new model. Here are some additional measures taken by Bitmain to produce optimal performance as things heat up:

• The S21 has twice as powerful fans compared to most S19 models
  • Naturally, this requires a bit more wattage.
  • This affects efficiency numbers, meaning the 17.5 J/THs is more accessible during immersion cooling, where fans are removed. We’ll go deeper into this later.
• The ASIC chips are covered with a thermal paste, and the heatsink is mounted with spring screws, ensuring even pressure on each ASIC chip
  • Both actions improve cooling and heat dissipation.
  • If Bitmain used heatsinks with heat pipes, we would likely see even more improvement here

SUMMARY: The machine’s hardware is not the only way to regulate temperature, as the S21’s stock firmware has some improvements as well.

Firmware

Stock firmware

Overall, the stock firmware on the S21 is pretty similar to the S19’s. There were no major changes, but a few things were improved upon.

• If the S21 begins to overheat, the stock firmware automatically tries to send it into low power mode
  • Remind you of anything? 😏- we introduced this feature in our firmware over two years ago in 2022, and our DPS is still more flexible in its settings and capabilities.
• The GUI and firmware is now better equipped for error handling, allowing for easier tracking of miner performance. The dashboard has a "warning" section for displaying errors
• The new firmware also lets users relatively manage downclocking based on the percentage they’d like to lower their power consumption.
• Still, the GUI is underwhelming considering the other technology that is improving in the bitcoin space.

Braiins OS Custom S21 firmware

Braiins recently added the Antminer S21 to its arsenal of support in Braiins OS. This custom firmware gets more out of the hardware, while adding features like DPS or cold climate performance boosts.

SUMMARY: Bitmain isn’t known for its firmware though, as some others pair with their products best.

Performance review

All of this analysis is nothing without the machine’s performance:

• Through testing, Braiins was unable to reach the sticker efficiency (17.5 J/THs) on the S21 running air-cooled with stock firmware and default power
  • The best we saw was 18 J/THs on stock firmware and default power, which still beats most other options on the market.
  • As stated above, immersion-cooling would likely get miners to that 17.5 J/THs number, with no fans necessary.
• The S21 on Braiins OS performed at 17.6 J/THs on default power
  • Overclocking on Braiins OS is where we saw more promising efficiency results.
  • Braiins OS also offers Dynamic Performance Scaling, which improves:
    • Thermal cycling protection
    • Lifespan prolongation
    • Higher uptime
    • Rich configuration options
    • Optimal compatibility for curtailment and demand response needs
    • And more

SUMMARY: The best way to mine is with the optimal combination of electricity cost, power consumption, hardware, and firmware. The Antminer S21 is a great bet – especially paired with Braiins OS.

Overall judgment

The Antminer S21 looks like a better, stronger, and more efficient brother to the previous generation. It will be a terrific successor to the S19 generation and even better with our custom firmware.