DRAM system design: What is the principal advantage of address multiplexing in dynamic RAM (DRAM) devices?

Introduction / Context:
DRAMs often present large address spaces. To keep packages affordable and PCB routing manageable, designers use multiplexed addressing, where the row and column addresses share the same set of external pins and are strobed separately (RAS and CAS).

Given Data / Assumptions:

• Row/column addressing with RAS (row address strobe) and CAS (column address strobe).
• Large arrays would otherwise require many address pins.
• We seek the main benefit of multiplexing.

Concept / Approach:
By splitting an N-bit address into two N/2-bit phases, the total number of physical address pins is roughly halved. This directly reduces package pin count, enabling smaller, cheaper packages and more economical system interconnect. While multiplexing does not eliminate refresh (an inherent DRAM requirement) and does not, by itself, reduce access time, it does allow higher density memories in practical pinouts.

Step-by-Step Solution:

Verification / Alternative check:
Compare historical non-multiplexed memories to modern DRAM: pin count scales poorly without multiplexing; JEDEC standards emphasize RAS/CAS over dedicated lines.

Why Other Options Are Wrong:

• Reduced access time: Multiplexing adds control phases; it does not inherently speed up access.
• Reduced refresh requirement: Refresh is required regardless of addressing scheme.
• No chip-select needed: DRAMs still need CS or bank/CS equivalents for proper system operation.

Common Pitfalls:
Assuming any pin-saving technique improves raw speed; often it is a packaging and cost optimization, not a timing optimization.

Final Answer:
reduced pin count and decrease in package size