Why dynamic RAMs use a multiplexed address bus Most DRAMs present row and column addresses on shared pins (multiplexed). The primary reason for this design choice is:

Introduction / Context:DRAM density scales with the number of memory cells, but package pin count adds cost and size. Multiplexing addresses (using RAS/CAS strobes) reduces the number of external pins while still selecting a unique cell.

Given Data / Assumptions:

• DRAM cells are organized in a 2D array with row and column selection.
• External pins are limited; sharing pins for row and column addresses halves the address pins needed.
• RAS (row address strobe) and CAS (column address strobe) latch the multiplexed halves.

Concept / Approach:Provide the row address on the address pins, latch with RAS; then provide the column address on the same pins, latch with CAS. This minimizes package pins and cost, enabling higher densities per package.

Step-by-Step Solution:Split N-bit address into row and column halves.Present row → assert RAS to latch.Present column → assert CAS to latch.Access cell at [row, column] while using fewer pins.

Verification / Alternative check:DRAM datasheets and timing diagrams show multiplexed address cycles with RAS/CAS, a standard since early DRAM generations.

Why Other Options Are Wrong:It is not the only possible way; it is a cost/pin optimization.Multiplexing does not inherently increase raw speed; it adds timing overhead.It does not remove the need for refresh; DRAM still requires periodic refresh.

Common Pitfalls:Assuming multiplexing is a speed feature; it is primarily about pin economy and density.

Final Answer:to keep the number of pins on the chip to a minimum