Cache Writing Methods

Often, we don't only read the value of a variable but also change it. A dirty cache block is a cache block that has been modified (e.g., by having one of its variables changed) in the cache but not yet updated in the main memory.

There are two general approaches as to when we should update RAM with those changes. They are called cache write policies or methods:

• Write-Through: Every change in cache is immediately done to main memory, too, ensuring consistency between cache and memory. This method increases memory traffic but simplifies data management.
• Write-Back: Modified data is written to main memory only when the cache block is evicted (= replaced by another RAM block,) which reduces memory traffic. A dirty bit is used to track whether a block needs to be written back, or if it's up to date in RAM.

Different computer architectures will benefit from different policies: the builders of an architecture need to run experiments to see which works faster on their particular computer.