Dynamic RAM is denser than static RAM, but needs to be refreshed every few milliseconds to avoid losing data. How many milliseconds, exactly? If the answer has changed over time, then I'm interested in what it was on the RAM chips used in the seventies and eighties.
What prompted the question was that I was under the impression some computers used the video circuitry to do the refresh, which would suggest it sufficed to do it once per 60 Hz frame, which would be about 16 ms, but according to http://www.jagregory.com/abrash-black-book/
Each DRAM chip in the PC must be completely refreshed about once every four milliseconds in order to ensure the integrity of the data it stores.
Was 4 ms the typical figure for standard DRAM chips?