Välimuistilohko

Välimuistilohko, known in English as a cache line, is the smallest unit of data that can be transferred between the main memory and the processor cache in a computer system. When the processor needs to access data, it doesn't fetch individual bytes or words. Instead, it fetches an entire cache line, which typically consists of 32, 64, or 128 bytes. This is done because of the principle of spatial locality, which states that if a particular memory location is accessed, it's likely that nearby memory locations will also be accessed soon.

The use of cache lines significantly improves performance by reducing the number of memory accesses. By bringing a block of data into the cache at once, subsequent accesses to data within that same block can be served directly from the much faster cache, avoiding the slower access to main memory. When the processor modifies data within a cache line, this change needs to be eventually written back to main memory. The management of these updates and ensuring consistency across multiple caches and main memory is handled by cache coherency protocols.

The size of a cache line is a design parameter that balances the benefits of spatial locality against the overhead of transferring larger blocks of data. A larger cache line can exploit spatial locality more effectively but may also waste cache space if only a small portion of the line is actually used. Conversely, a smaller cache line might lead to more cache misses and increased memory traffic.