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The Intel 8087 math coprocessor (1980) had too much microcode to fit into a standard ROM. It was implemented with a special ROM that stored two bits per transis
by kens 3y ago
The Intel 8087 math coprocessor (1980) had too much microcode to fit into a standard ROM. It was implemented with a special ROM that stored two bits per transistor by using four different transistor sizes, almost doubling the density. Each value read from the ROM was thresholded to generate two output bits. This technique was also used in the iAPX 432's I/O processor chip.
- yonatan8070 3y agoIsn't this exactly what modern TLC/QLC do?
- colejohnson66 3y agoSame concept for reading - threshold regions indicate multiple bit values, but different for storage. The 8087 used physically different transistor sizes[0] to read a voltage level that "stored" two bits inside four threshold regions. MLC/TLC/QLC/PLC use a single transistor but charge the gate to a different "analog" voltage that is between 2^n threshold regions - MLC has four (two bits), TLC has eight (three bits), QLC has 16 (four bits), and PLC has 32 (five bits). [0]: https://www.righto.com/2018/09/two-bits-per-transistor-high-density.html https://www.righto.com/2018/09/two-bits-per-transistor-high-...
- formerly_proven 3y agoNB-ROM-shenanigans are very traditional. The Tektronix 7000 readout (1969) managed to encode the stroke of an entire letter with just a few transistors. Here's the letter 3, encoded in 24 transistors: https://w140.com/tekwiki/images/e/e0/7000-readout-chargen-circuit-1.jpg https://w140.com/tekwiki/images/e/e0/7000-readout-chargen-ci... This uses multi-emitter transistors to encode discrete current ratios (which are then interpolated across groups by smoothly ramping base currents between points, turning them into strokes), all connections done in the metal layer, so the silicon was the same for all ROM chips. https://w140.com/tekwiki/wiki/7000_series_readout_system https://w140.com/tekwiki/wiki/7000_series_readout_system
- jojobas 3y agoROMs were non-binary before it was cool.
- eternityforest 3y agoThey were not messing around with the analog wizardry back in the day! Before even the first microcontroller they were doing this!