Definition
BM1368 is Bitmain’s 5 nm SHA-256 mining ASIC (silicon chip ID 0x1368), the workhorse die behind the air-cooled Antminer S21 family. It sits between the BM1366 generation and the newer BM1370, computing the double-SHA-256 hashes that Bitcoin’s proof-of-work depends on.
Where the BM1368 is used
The BM1368 die powers a broad slice of the current Antminer lineup. It is the chip inside the base S21, the S21+, the S21 Hydro, and the air-cooled T21, and it also appears in later Amlogic-controlled S19-class units (S19 Pro and S19i variants). In the open-source world, the same silicon turns up as a single chip in the Bitaxe Gamma, where one BM1368 replaces the hundred-plus chips of an industrial hashboard with a tiny solo-mining device.
Note the family split: the BM1368 is the base-S21 die, while the higher-binned BM1370 (a separate, higher-performance die) is reserved for the S21 Pro. The T21 sometimes gets miscredited to the BM1370, but it carries the BM1368 — the two share a silicon envelope but are distinct dies on different hashboard families.
What the silicon looks like
Each BM1368 packs roughly 1,280 hashing cores (organized as 80 large cores subdivided into 16 small cores each), confirmed against an S21 factory test fixture. On a stock S21 hashboard, 108 BM1368 chips are wired in a single serial chain, and the board is divided into 12 voltage domains so the control board can manage current across groups of chips rather than one chip at a time. A complete S21 carries three such boards.
Like the rest of its ASIC chip generation, the BM1368 receives a full 82-byte block header over its serial interface and computes the midstate internally — older chips like the BM1387 relied on the host control board to pre-compute midstates. It also performs on-chip version rolling (the hardware ASICBoost technique standardized as BIP 320), automatically iterating the version-field bits to search more of the nonce space per job. This is a defining trait of the BM1362/BM1366/BM1368/BM1370 family and a key reason these chips are so efficient at saturating their hash pipelines.
Power, efficiency, and tuning
At its factory nameplate, a BM1368-based S21 runs each board near 525 MHz at roughly 13.8 V, with the full miner drawing about 3,500 W for around 200 TH/s — an efficiency in the neighborhood of 17.5 J/TH. Underclocking is where the chip shines: dropping to about 480 MHz at 13.4 V trims the unit to roughly 3,000 W and 175 TH/s, improving efficiency to around 17.1 J/TH. Because the chip exposes a tunable PLL frequency and per-domain voltage, custom firmware can walk these operating points to chase efficiency, hashrate, or a target power envelope.
One hardware detail matters for anyone servicing an S21: the BM1368 boards use a “no-PIC” design where voltage is set by audio-class DAC controllers on the I2C bus rather than a dedicated PIC microcontroller. On these boards, blindly toggling chain-reset GPIO lines can disrupt the voltage rails — a trap worth knowing before you start poking at a dead hashboard.
Why it matters for miners
The BM1368 is, in practical terms, the chip you are buying when you buy a current-generation air-cooled Antminer S21. Understanding its core count, chain length, and tuning headroom helps you reason about real-world efficiency, plan repairs at the hashboard level, and judge whether a sub-200 TH/s reading means a tuning issue or a failing chain. The same knowledge transfers directly to the open-source Bitaxe, where a single BM1368 makes solo lottery mining approachable for home setups.
If you are weighing a BM1368-class S21 against other hardware, our miner catalog lays out the full S21 family side by side, and the open-source mining gear section covers Bitaxe options for those who want one BM1368 on their desk. To get the most out of whatever chip you run, see how tuning and firmware choices stack up in our firmware comparison — the right configuration is what turns raw silicon into sustainable hashrate.
In Simple Terms
A Bitmain chip used in Antminer S21 variants and the Bitaxe Gamma open-source miner.
BM1368 is Bitmain's 5 nm SHA-256 mining ASIC (silicon chip ID 0x1368), the workhorse die behind the air-cooled Antminer S21 family. It sits between the BM1366 generation and the newer BM1370, computing the double-SHA-256 hashes that Bitcoin's proof-of-work depends on.
Where the BM1368 is used
The BM1368 die powers a broad slice of the current Antminer lineup. It is the chip inside the base S21, the S21+, the S21 Hydro, and the air-cooled T21, and it also appears in later Amlogic-controlled S19-class units (S19 Pro and S19i variants). In the open-source world, the same silicon turns up as a single chip in the Bitaxe Gamma, where one BM1368 replaces the hundred-plus chips of an industrial hashboard with a tiny solo-mining device.
Note the family split: the BM1368 is the base-S21 die, while the higher-binned BM1370 (a separate, higher-performance die) is reserved for the S21 Pro. The T21 sometimes gets miscredited to the BM1370, but it carries the BM1368 — the two share a silicon envelope but are distinct dies on different hashboard families.
What the silicon looks like
Each BM1368 packs roughly 1,280 hashing cores (organized as 80 large cores subdivided into 16 small cores each), confirmed against an S21 factory test fixture. On a stock S21 hashboard, 108 BM1368 chips are wired in a single serial chain, and the board is divided into 12 voltage domains so the control board can manage current across groups of chips rather than one chip at a time. A complete S21 carries three such boards.
Like the rest of its ASIC chip generation, the BM1368 receives a full 82-byte block header over its serial interface and computes the midstate internally — older chips like the BM1387 relied on the host control board to pre-compute midstates. It also performs on-chip version rolling (the hardware ASICBoost technique standardized as BIP 320), automatically iterating the version-field bits to search more of the nonce space per job. This is a defining trait of the BM1362/BM1366/BM1368/BM1370 family and a key reason these chips are so efficient at saturating their hash pipelines.
Power, efficiency, and tuning
At its factory nameplate, a BM1368-based S21 runs each board near 525 MHz at roughly 13.8 V, with the full miner drawing about 3,500 W for around 200 TH/s — an efficiency in the neighborhood of 17.5 J/TH. Underclocking is where the chip shines: dropping to about 480 MHz at 13.4 V trims the unit to roughly 3,000 W and 175 TH/s, improving efficiency to around 17.1 J/TH. Because the chip exposes a tunable PLL frequency and per-domain voltage, custom firmware can walk these operating points to chase efficiency, hashrate, or a target power envelope.
One hardware detail matters for anyone servicing an S21: the BM1368 boards use a "no-PIC" design where voltage is set by audio-class DAC controllers on the I2C bus rather than a dedicated PIC microcontroller. On these boards, blindly toggling chain-reset GPIO lines can disrupt the voltage rails — a trap worth knowing before you start poking at a dead hashboard.
Why it matters for miners
The BM1368 is, in practical terms, the chip you are buying when you buy a current-generation air-cooled Antminer S21. Understanding its core count, chain length, and tuning headroom helps you reason about real-world efficiency, plan repairs at the hashboard level, and judge whether a sub-200 TH/s reading means a tuning issue or a failing chain. The same knowledge transfers directly to the open-source Bitaxe, where a single BM1368 makes solo lottery mining approachable for home setups.
If you are weighing a BM1368-class S21 against other hardware, our miner catalog lays out the full S21 family side by side, and the open-source mining gear section covers Bitaxe options for those who want one BM1368 on their desk. To get the most out of whatever chip you run, see how tuning and firmware choices stack up in our firmware comparison — the right configuration is what turns raw silicon into sustainable hashrate.