Definition
Fetch Policy
A fetch policy determines when a page is brought into main memory (RAM) from secondary storage.
Strategies
Demand Paging
A page is loaded only when referenced. Only required pages occupy memory, but initial page faults may be high.
Prepaging
Pages beyond the requested one are loaded in advance based on the principle of locality. Reduces page faults if the assumption holds, but wastes I/O and memory if pre-fetched pages are unused.
Comparison
Modern Practice
Most operating systems use demand paging as the primary strategy, often combined with small-scale prepaging (e.g., reading a few adjacent pages) during disk reads to improve efficiency.