I/O performance engineering: Block caches (buffer caches) in an operating system are primarily used for what purpose?

Introduction / Context:
Disks are orders of magnitude slower than CPU and DRAM. Operating systems use buffer caches (block caches) to reduce I/O latency and increase throughput by keeping recently accessed disk blocks in memory and coalescing writes efficiently.

Given Data / Assumptions:

• We refer to OS-level caches of disk blocks, not CPU caches.
• Goal is to understand their primary role.
• Disk latencies include seek and rotational delays.

Concept / Approach:

The buffer cache stores frequently used blocks, enabling read hits from RAM and delayed, batched writes (write-back or write-through depending on policy). It also allows read-ahead and elevator scheduling to reduce seek overhead, dramatically improving perceived disk performance.

Step-by-Step Solution:

Verification / Alternative check:

Performance monitoring shows higher cache hit rates correlate with lower average I/O times and fewer physical disk operations.

Why Other Options Are Wrong:

• Handle interrupts: role of interrupt handlers, not buffer caches.
• Increase main memory capacity: caching uses memory; it does not add capacity.
• Speed up main memory reads: DRAM accesses do not need a buffer cache; CPU caches handle that layer.

Common Pitfalls:

Confusing buffer cache with page cache versus CPU L1/L2 caches; ignoring write-ordering and durability trade-offs in write-back policies.

Final Answer:

to improve disk performance