Ken Shirriff's post reverse-engineers the 8087 FXCH microcode, revealing detailed micro-instruction flow, ROM size, and die architecture.
Open-source z386 reconstructs the 80386 around original microcode in FPGA, enabling real DOS software and Doom, with a compact 16KB VIPT L1 cache and a 37-bit microcode word design, benchmarked against ao486.
Disassembles the 80386 microcode, revealing a very large microcode ROM (94,720 bits) and 215 entry points with full microcode coverage, plus a potential IO-port permission bug and open-source references.
Reverse-engineering the Intel 8087 reveals an eight-entry, 80-bit stack with push/pop rules, a carry-lookahead adder and toggle-based increment/decrement, plus a dense, multi-layer RAM-like register file and a semi-analog microcode ROM; the design produced stack overflow/underflow pitfalls that affected compiler and OS support, and was eventually superseded by SSE/AVX.
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