BIP Draft: 24 nVersion bits for general purpose use

bip-0320.mediawiki

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   Type: Specification
   Assigned: 2018-03-01
   License: BSD-3-Clause OR CC0-1.0
+  Proposed-Replacement: ?
 </pre>
 
 ==Abstract==

bip-XXXX.mediawiki

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+<pre>
+  BIP: ?
+  Title: 24 nVersion bits for general purpose use
+  Authors: Matt Corallo <bips@bluematt.me>
+  Status: Draft
+  Type: Specification
+  Assigned: ?
+  License: BSD-3-Clause OR CC0-1.0
+  Discussion: 2026-02-26: https://gnusha.org/pi/bitcoindev/6fa0cb45-37d6-4b41-9ff8-03730fd96d6e@mattcorallo.com/
+  Replaces: 320
+</pre>
+
+==Abstract==
+
+24 bits are reserved in the nVersion field as extra nonce space for miners, providing for additional
+hashrate with header-only mining without relying on rolling nTime more often than once per second.
+
+==Motivation==
+
+BIP 320 defined 16 bits of nVersion as nonce space for additional nonce space. It turns out that
+this isn't enough, as some devices have started using 7 bits from nTime for extra nonce space (see
+https://github.com/stratum-mining/sv2-spec/discussions/187). Given there's limited utility in 16
+bits of nVersion space for signaling, instead here we offer 24 bits of nVersion space as extra
+nonce space.
+
+==Specification==
+
+24 bits from the block header nVersion field, starting from 5 and ending at 28 inclusive
+(0x1fffffe0), are reserved for nonce use and removed from BIP8 and BIP9 specifications. A mask of
+0xe000001f should be applied to nVersion bits so bits 5-28 inclusive will be ignored for soft-fork
+signalling and unknown soft-fork warnings.
+
+==Rationale==
+
+Headers-only mining avoids mining devices (either ASICs or the firmware) from having to concern
+themselves with the vast space of consensus logic (handling transactions, merkle trees, etc). It is
+widely deployed in ASICs, but requires a substantial number of jobs fed across an entire device,
+keeping the ASIC controller busy. Providing additional nonce space for the ASICs to roll without
+needing fresh work from the controller may simplify ASIC design somewhat, and as been apparently
+adopted in some miners by using extra space in nTime as extra nonce space. Doing so in nVersion
+instead is preferable to using nTime.
+
+==Backwards Compatibility==
+
+Non-upgraded nodes will interpret the reserved bits of this proposal as signals for soft forks, and
+may additionally activate the warning system for unknown soft forks.
+
+At the time of writing no soft forks which are being actively signaled for are using any of the 24
+bits reserved in this BIP. Future soft forks SHOULD NOT utilize those bits for activation signaling.
+
+==Acknowledgements==
+
+Timo Hanke and Sergio Lerner for originally proposing 15-bit extra nNonce2. Btc Drak for writing BIP
+320.
+
+==Copyright==
+
+This document is dual licensed as BSD 3-clause, and Creative Commons CC0 1.0 Universal.