Introduction to Instruction Set Architectures
One of the key performance bottlenecks in computer systems is memory access time. In order to reduce memory access time, a memory hierarchy is used. Memory hierarchy is a concept where the memory is organized in multiple layers, each layer having a different access time and capacity. The memory hierarchy includes registers, cache memory, main memory, and secondary memory. Registers are the fastest and smallest memory type, followed by cache memory. Main memory is slower than cache memory, but has a larger capacity. Secondary memory is the slowest and has the largest capacity.
Caching is an optimization technique used in computer systems to speed up memory access. The idea behind caching is to store frequently accessed data in a smaller and faster memory. This is done by dividing the memory into blocks and storing them in the cache. When a program requests data, the processor first checks if the data is present in the cache. If the data is present in the cache, it is fetched from the cache memory, which is faster than main memory. If the data is not present in the cache, it is fetched from the main memory and stored in the cache for future use.
There are different cache replacement policies that are used to decide which data to evict from the cache when the cache is full. These policies include LRU (Least Recently Used), FIFO (First In First Out), and random replacement. LRU is the most commonly used policy, where the cache replaces the data that has not been accessed for the longest time.
Caching is used in various computer systems, including CPUs, hard disk drives, and web browsers. In CPUs, the cache is located closer to the processor, and is known as the CPU cache. In hard disk drives, the cache is used to buffer data between the disk and the system memory. In web browsers, the cache is used to store frequently accessed web pages, which reduces the loading time of the web page on subsequent visits.
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