Reverse-Engineering the Classic MK4116 16-Kilobit DRAM Chip
owl writes:
https://www.righto.com/2020/11/reverse-engineering-classic-mk4116-16.html
Back in the late 1970s, the most popular memory chip was Mostek's MK4116, holding a whopping (for the time) 16 kilobits. It provided storage for computers such as the Apple II, TRS-80, ZX Spectrum, Commodore PET, IBM PC, and Xerox Alto as well as video games such as Defender and Missile Command. To see how the chip is implemented I opened one up and reverse-engineered it. I expected the circuitry to be similar to other chips of the era, using standard NMOS gates, but it was much more complex than I expected, built from low-power dynamic logic. The MK4116 also used advanced manufacturing processes to fit 16,384 high-density memory cells on the chip.
[...] In dynamic RAM, each bit is stored in a capacitor with the bit's value, 0 or 1, represented by the voltage on the capacitor.3 The advantage of dynamic RAM is that each memory cell is very small, so a lot of data can be stored on one chip.4 The downside of dynamic RAM is that the charge on a capacitor leaks away after a few milliseconds. To avoid losing data, dynamic RAM must be constantly refreshed: bits are read from the capacitors, amplified, and then written back to the capacitors. For the MK4116, all the data must be refreshed every two milliseconds.
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