2116 and other old memory chips

OK... Static RAM is made from flip-flops. Which means that when you write data to it, you set some flip flops one way (for '1's) and some the other way (for '0's). And the flip-flops remain in that state until either you turn the power off or you write some other data to it. Dynamic RAM is made from capacitors. Generally, a '1' is represented by a charge on a capacitor, a '0' is a discharged capacitor. Writing data to DRAM involves charging some capacitors and discharging others. The problem is that all electronics has leakages. So the capacitors discharge themselves (in a few milliseconds). So you have to read each location periodically and write the data back again to 'refresh' the charge on the capacitors. Most (all?) DRAMs have internal circuitry to help with this (e.g. accessing a particular location will refresh a number of locations -- perhaps all those with the same pattern in the high-order half of the address). But you still have to do something -- on 'classic' DRAMs, you have to cycle the address inputs and apply RAS/ pulses (or at least that's the normal way). If you don't, you lose data. That's the difference. The contents of static RAM are maintained as long as power is applied. Dynamic RAM needs to be refreshed or it will forget. -tony