13.1. Kernel Buffering of File I/O: The Buffer Cache

When working with disk files, the read() and write() system calls don’t directly initiate disk access. Instead, they simply copy data between a user-space buffer and a buffer in the kernel buffer cache. For example, the following call transfers 3 bytes of data from a buffer in user-space memory to a buffer in kernel space:

write(fd, "abc", 3);