How Does RAM Work?
How memory finds, writes and forgets data
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Summary
RAM is the main memory where a computer temporarily keeps the data it is working on. It is made of billions of small boxes, each numbered with an address, and each box holds one byte (8 bits). The processor sends an address; the memory opens that address's row, and the data is read from or written to that row. Each bit is stored in a cell made of a transistor and a tiny capacitor: a full capacitor means 1, an empty one means 0. Because capacitors leak, the memory constantly refreshes its cells; when the power goes, everything is lost.
In depth
Random Access Memory gets its name from the fact that every address can be reached in the same time. The memory is made of cells arranged in rows and columns. The address goes to a decoder, which switches on the word line of just one row, connecting that row's cells to the bit lines. When reading, the charge in the cells flows onto the bit lines and sense amplifiers turn this tiny change into a 0 or a 1; when writing, the bit lines fill or empty the cells. The DRAM cell with one transistor and one capacitor, invented by Robert Dennard at IBM in 1966, is still used today. Because it leaks, it is refreshed every 64 milliseconds, and because reading drains it, it is written back after every read.
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