BM1387

BM1387 is Bitmain's first-generation 16 nm SHA-256 mining ASIC (silicon chip ID 0x1387), released in 2017 as the workhorse die behind the legendary Antminer S9 family. It computes the double-SHA-256 hashes that Bitcoin's proof-of-work depends on, and for several years it was the most widely deployed mining chip in the world. As a "Gen 1" die, it predates the on-chip refinements found in later Bitmain silicon, which is exactly what makes it a useful reference point for understanding how the architecture evolved.

Where the BM1387 is used

The BM1387 is the die inside the entire Antminer S9 lineage: the original S9, the S9i, the S9j, and the T9+. Two later refinements are worth knowing about. The S9 SE shipped with a chip labeled BM1391, and a revised S9j shipped with a chip labeled BM1393 — but both report the same 0x1387 chip ID and speak the identical BM1387 command and register surface. They are silicon-binning and process-shrink variants, register-compatible with the BM1387 for every wire-format purpose. In practice that means a control board or firmware written for the BM1387 will talk to all of them without modification.

What the silicon looks like

On a stock S9 hashboard, 63 BM1387 chips are wired in a single serial chain, and the board is split into 21 voltage domains — three chips per domain, each domain held at roughly 0.40 V. The domains are stacked in series so the control board manages current across groups of chips rather than one chip at a time. A complete S9 carries three such boards (189 chips total) and is driven by a Xilinx Zynq 7010 control board pairing a dual-core Cortex-A9 at 667 MHz with an Artix-7 FPGA over the standard 18-pin ribbon interface.

Each chip delivers roughly 75 GH/s, putting a full S9 in the 13–14 TH/s range at its stock operating point. One architectural detail separates the BM1387 from its descendants: it relies on the host control board to pre-compute the SHA-256 midstate and feed it over the serial link, where later ASIC chips such as the BM1368 compute the midstate internally. The BM1387 also lacks the hardware version rolling built into newer dies, so its overt-ASICBoost gains were handled differently rather than baked into the silicon's nonce search.

Power, efficiency, and tuning

At its factory nameplate the BM1387 lands around 98 J/TH — respectable for 2017, but several times less efficient than current 5 nm and 3 nm silicon. Because efficiency is the S9's weak point, undervolting and underclocking became the dominant way to keep these machines economical: dropping per-domain voltage and PLL frequency trades raw hashrate for a meaningfully better J/TH figure, which is why so much aftermarket S9 firmware focuses on autotuning the operating point. Voltage is set per domain, not per chip, so any tuning change moves three chips at once.

Why it matters for miners

The S9 was the most-cloned mining board in history, which has a direct consequence on the used market: re-balled and harvested BM1387 dies are common, and "refurbished" boards are not always what they claim to be. Before trusting one, cross-check the tell-tale 63-chip / 21-domain layout and confirm the U3 PIC controller (a PIC16F1704) is present and genuine — unlike the later no-PIC S21 boards, S9-class hashboards use a PIC to manage chain power-up. When sourcing replacement chips, keep a single board to one silicon bin: BM1387, BM1391, and BM1393 dies are interchangeable at the protocol layer, but mixing bins on one board shifts the achievable frequency and voltage envelope and makes a board harder to tune cleanly.

Understanding the BM1387's chain length, domain map, and PIC layout is what turns a dead S9 hashboard from a mystery into a methodical repair. If you are weighing older S9-class hardware against current-generation machines, our miner catalog lays the options out side by side, and the firmware comparison shows how tuning choices reshape what aging silicon like the BM1387 can still deliver.