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         * 3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway          */         clear_cpu_cap(c, 0*32+31); as has Centaur and Cyrix.  Amazingly, besides formatting, this appears to be unchanged since "Massive cleanup of CPU detection and bug handling; Transmeta CPU detection, H. Peter Anvin , November 2000". https://github.com/schwabe/davej-history/commit/67ad24e6d39c3bc4618e7eb0563ccde3d76d0a51#diff-ab4c065cef7ebcd6d255c47ed4c3c0a77da8ad3df004dab9a183cc88814730ff is the only working mirror I can find online. When AMD added 3DNow, it was only in extended CPUID.  https://datasheets.chipdb.org/AMD/All%20CPU/20734j.pdf notes that other vendors implemented 3DNow, and Centaur does have extra logic to re-activate 3DNow. I realise I'm asking a lot, but do you remember why this clear of PBE was added? It looks out of place even at the time of adding.  The x86_capability backing memory was zeroed shortly before, and only only written into by a correct looking cpuid(1) invocation. Was there really a CPU which misreported it in basic CPUID, or is there some other reason for it? Thanks, ~Andrew