CacheLinien

CacheLinien, or cache lines, are the basic unit of data transfer between a computer's memory hierarchy and its caches. A cache line represents a contiguous block of memory that is loaded and stored as a single unit. In modern processors, a cache line is typically 32, 64, or 128 bytes in size, depending on the architecture.

Each line stored in a cache carries metadata, such as a tag that identifies the memory region, a valid bit, and, in write-back caches, a dirty bit indicating modifications not yet written to main memory. Caches are organized into levels (L1, L2, L3) and into sets within each level; the hardware maps an address to a particular line by calculating an index from the address.

Data locality and performance depend on line size and access patterns. When a processor accesses memory, it loads a line from main memory into the cache. Subsequent accesses to nearby addresses may reuse the same line, reducing latency. Conversely, stride-1 access through large arrays tends to be efficient, while large or irregular strides can cause cache misses or conflict misses in set-associative or direct-mapped caches.

Programming and optimization considerations include aligning data structures to cache-line boundaries, padding to avoid false sharing in multi-threaded code, and organizing loops to access memory sequentially. Some architectures offer prefetching hints to pre-load future lines. The choice of line size and data layout can have a substantial impact on performance.

While the concept is hardware-dependent, the principle of cache lines as the granularity of data transfer is universal across modern CPUs. Understanding CacheLinien helps explain performance differences between seemingly similar algorithms.