Q. Read-and-write memory?

Writing is the same as storing data intomemory and reading is the same as retrieving the data later. RAM is said to be volatile because its contents are retained only as long as power is present. A RAM device is a collection of 2ⁿ addressable storage locations, each of which contains k bits. Its block diagram is shown in Figure, in which each cell may be a flip-flop or a capacitor, and n address lines are decoded to select k cells. A static RAM, in which each cell is a flip-flop, is the read-and-write memory that retains its data so long as the power is applied, without any further action needed from the computer. Static RAMis used in microprocessor-based systems requiring small memory. Common static-RAMsizes are 2K × 8, 8K × 8, and 32K × 8, where K stands for 2¹⁰ = 1024. A dynamic RAM, in which each cell is a capacitor (which leaks charges and therefore requires continuous refreshing from the computer to maintain its value), is the read-and-write memory that is used in large memory systems due to its lower cost and greater density. Common dynamic-RAMpackages are available in 16K-bit, 64K-bit, 256K-bit, and 1M-bit (whereMstands for mega = 2²⁰ ) sizes.