# Why the Page Cache Speeds Up Second Reads

## The Basic Idea

The **page cache** is an in-memory cache maintained by the operating system that stores recently accessed file data in RAM. When a file is read, its contents are copied from disk into memory pages; subsequent reads of the same data can be served directly from RAM.

## First Read (Slow)

1. Application calls `read()`.
2. The OS checks the page cache — miss.
3. Data must be fetched from disk:
   - Disk seek/rotation latency (HDDs: milliseconds)
   - Or flash access latency (SSDs: