Which memory in the computer memory hierarchy provides the fastest access time in typical systems?

Introduction:
Computer systems use a memory hierarchy to balance speed, capacity, and cost. This question tests recognition of which tier offers the lowest latency for the CPU.

Given Data / Assumptions:

• Options: cache, primary (main memory/RAM), mass storage (SSD/HDD), offline backup (tape/external).
• Typical modern CPU with L1/L2/L3 caches.

Concept / Approach:

L1 cache resides closest to the CPU core and offers the smallest access latency, followed by L2, L3, then DRAM (primary memory). Mass storage devices are orders of magnitude slower, and offline backups are slower still and not directly addressable by the CPU.

Step-by-Step Solution:

Verification / Alternative check:

Microbenchmarks consistently show nanosecond-scale cache hits versus tens of nanoseconds for DRAM and micro/millisecond scales for storage.

Why Other Options Are Wrong:

Primary (RAM) is slower than cache. Mass storage and offline backup are much slower and not CPU-cached.

Common Pitfalls:

Equating higher capacity with higher speed; confusing cache with system-level disk caches.

Final Answer:

Cache