This is shared Antminer S21 Series reference material covering 10 models. Components, supply voltage/phase, PSU, cooling and service procedures vary by model and revision. Use the exact model nameplate and OEM manual; shared examples do not establish compatibility.
Firmware is how you upgrade, recover, and optimize a fleet. Stock keeps units on spec; custom firmware (Braiins OS+, Vnish, LuxOS) adds per-chip auto-tuning for better efficiency - at a small dev fee and a voided warranty.
Bitmain's official firmware, upgraded by uploading the correct signed image for the EXACT model in the web UI. Techs update to fix bugs, patch security, or improve efficiency.
The field recovery step for a control board that won't boot, is boot-looping, or has corrupted firmware the web UI can't fix. It's a firmware RESTORE, not a repair.
Custom firmware from Braiins (makers of Braiins/Slush Pool). Partly open-source and the reference implementation of Stratum V2. Antminer only - no Whatsminer. Adds per-chip autotuning, power/hashrate targeting, and DPS thermal scaling.
Independent closed-source Antminer firmware known for the BROADEST model coverage, fastest support for brand-new models, aggressive overclocking, and a polished dashboard. Primarily Antminer (incl. L3/L7/L9 Scrypt), and also covers Whatsminer M3x/M5x/M6x.
Commercial firmware from Luxor Technology - the only ASIC firmware with SOC 2 Type 2 certification, aimed at enterprise fleets. Antminer S19/S21 (+hydro) and now SELECT Whatsminer (M50 first, M60/M70 rolling out).