Hard fault意思

"Hard fault" is a term used in the context of virtual memory management in computer systems. It refers to a type of page fault that occurs when a process attempts to access a memory page that is not currently resident in physical memory (RAM).

When a process is running, the operating system manages its memory usage by keeping some pages of the process's virtual address space in physical memory for quick access, and swapping other pages out to disk as needed to make room. If the process tries to access a page that is not currently in memory, a page fault occurs.

A hard fault occurs when the page that is not currently in memory is not in the process's page table or is marked as invalid. In this case, the operating system must load the page from disk into physical memory, which is a more time-consuming operation than handling a soft fault.

Soft faults, on the other hand, refer to page faults where the required page is present in the process's page table but is not currently in physical memory. In this case, the page can be quickly brought into memory from the disk cache or from swap space, if necessary.

Hard faults are generally considered to be more expensive in terms of performance because they involve reading data from a slower storage medium (such as a hard disk or SSD), which can lead to increased latency and reduced system performance. Therefore, minimizing hard faults is an important aspect of optimizing system performance, especially in systems with limited physical memory or high memory usage.