How RAM works?

Answer 1

RAM (Random Access Memory) is made of cells where each cell has a capacitor and a transistor. The capacitor can be thought of as being a cup while the transistor is a tap that can either fill the cup or empty the cup. The cup is filled with an electric charge to denote the value 1, and emptied to denote the value 0. Thus each cell denotes 1 bit (binary digit) of information. The cup, however, is incredibly leaky, and the charge will quickly drain away within a few milliseconds. To maintain the state of each bit, the RAM must be constantly refreshed. During each refresh cycle, if a bit has sufficient charge (more than 50%) then it is refilled, otherwise it is allowed to drain away completely. Refreshing RAM is done in cycles measured in nanoseconds, such as 80 nanoseconds. That is, it takes 80 billionths of a second to completely refresh the RAM.

Cells are arranged in an array of rows and columns. To write any one cell, a row access selector (RAS) selects the appropriate row while a charge is passed through the associated column access selector (CAS). To read a bit, a sense-amplifier detects the level of charge at the intersection of the RAS and CAS. The CAS detects the bit lines while the RAS detects word lines (32 bits in a 32-bit word). Thus to read successive bits in a word line, only the CAS needs to change.