Disk Storage vs. Main Memory Which statement is false when comparing magnetic/SSD disk storage to main memory (RAM)?

Introduction / Context:
Choosing appropriate storage requires understanding trade-offs among speed, capacity, volatility, and cost. Comparing disk storage and RAM highlights why systems use hierarchical memory.

Given Data / Assumptions:

• Disk may refer to HDD or SSD; RAM refers to volatile DRAM.
• We compare typical characteristics, not exotic hardware.

Concept / Approach:
RAM provides much lower latency and higher bandwidth than disk but is volatile and more expensive per bit. Disk (especially HDD) is far slower but cheaper and non-volatile. SSDs improve speed but still exhibit higher latency than DRAM.

Step-by-Step Solution:
Evaluate non-volatility: Disk is non-volatile; RAM loses data on power-off.Evaluate capacity: Disks commonly provide far larger capacities than RAM.Evaluate cost per bit: Disk cost/bit is lower than RAM.Evaluate performance: RAM access latency/bandwidth is superior; therefore “disk is faster” is false.

Verification / Alternative check:
Typical DRAM latency is on the order of tens of nanoseconds; SSD latency is microseconds; HDD access involves milliseconds—orders of magnitude slower than RAM.

Why Other Options Are Wrong:
Option A: Correct—disks are non-volatile.Option B: Correct—disks usually provide much larger capacity.Option C: Correct—cost per bit is lower for disks than for DRAM.Option E: Not applicable because Option D is the false statement.

Common Pitfalls:

• Assuming SSD speed matches RAM speed; SSDs are faster than HDDs but still slower than DRAM.
• Confusing throughput (MB/s) with latency; both favor RAM.
• Equating cache memory with main memory; CPU caches are even faster than DRAM.

Final Answer:
Disk is faster than main memory.