Post B6pYx96CeMUBNSw38q by kenshirriff@oldbytes.space
 (DIR) More posts by kenshirriff@oldbytes.space
 (DIR) Post #B6pYx96CeMUBNSw38q by kenshirriff@oldbytes.space
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       In the 1980s, if you wanted your IBM PC to be faster for spreadsheets or CAD, you could buy the Intel 8087 floating-point chip. Internally, the chip runs special code called microcode. We opened the chip, extracted the microcode, and are figuring out how it works. 1/n
       
 (DIR) Post #B6pYxAF6OlCMvM6feS by kenshirriff@oldbytes.space
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       A microscope reveals the complex circuitry of the 8087 chip. The microcode ROM in the center holds the micro-instructions. It executes these micro-instructions to add, subtract, compute square roots, arctangents, and so forth. 2/n
       
 (DIR) Post #B6pYxAjaZPaKRuN1Ae by kenshirriff@oldbytes.space
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       A close-up of the microcode ROM shows the individual bits. Unlike most ROMs, the 8087 uses four transistor sizes, letting it store two bits per transistor. This complex, semi-analog approach was necessary to fit all the data into the chip; the 8087 pushed the limits of 1980 technology. 3/n
       
 (DIR) Post #B6pYxBJ2RbwQDqxKQS by kenshirriff@oldbytes.space
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       We are reverse-engineering the meaning of the 8087's microcode. For more details, see my latest article:https://www.righto.com/2026/05/microcode-inside-intel-8087-floating.html
       
 (DIR) Post #B6pYxBq0T2JRs6NeoS by kenshirriff@oldbytes.space
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       I did this work with the Opcode Collective, especially Smartest Blob and Gloriouscow.The full ROM image: https://8087.martypc.net/#dzi=tiles%2Ftiles.dziA description of the 8087 microcode: https://github.com/a-mcego/granite/blob/main/tools/8087mc/bin/8087.md
       
 (DIR) Post #B6ppNBvIN4xwvqH5km by azonenberg@ioc.exchange
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       @kenshirriff wait is this like MLC mask rom??
       
 (DIR) Post #B6qbsYrhv0aArXcXNg by tnt@chaos.social
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       @azonenberg @kenshirriff That was my exact reaction !  First time I ever hear of such thing.