Prefetched

Prefetched refers to data or resources that have been retrieved before they are actually needed, typically by a system component or program that anticipates future requests. The aim is to reduce latency and improve throughput by overlapping input/output with computation.

In CPU design, hardware prefetchers monitor memory access patterns and fetch data into caches before the core requests it, concealing memory latency. Prefetched blocks may populate one of several cache levels (for example L1 or L2) and improve steady-state throughput for predictable access patterns.

In software and networks, prefetching is used to speed up user experiences and data processing. Web browsers may prefetch DNS records or fetch linked resources in advance, guided by hints such as prefetch or rel-prefetch directives. Content delivery networks and browsers may perform speculative fetches to shorten subsequent load times.

In storage systems and databases, read-ahead and prefetching pull data blocks into memory in anticipation of future reads. This can reduce disk I/O and accelerate queries, but incorrect predictions can waste bandwidth, memory, or cache space.

In operating systems, prefetching can improve startup times and file access performance by pre-loading frequently used data or code paths. Some operating systems maintain prefetch caches or similar mechanisms to optimize common workflows.

Limitations include the need for accurate prediction, the potential for wasted resources under irregular workloads, and possible privacy or security considerations when prefetching behavior reveals user activity. Overall, prefetched data is a proactive optimization used across hardware and software to reduce perceived latency.