Inside the Machine

Write Policies: Write-Through vs. Write-Back

So far, this entire chapter has dealt with only one type of memory traffic: loads, or requests for data from memory. I’ve talked only about loads because they make up the vast majority of memory traffic. The remainder of memory traffic is made up of stores, which in simple uniprocessor systems are much easier to deal with. In this section, I’ll explain how to handle stores in single-processor systems with just an L1. When you throw in more caches and multiple processors, things get more complicated than I want to go into here.

Once a retrieved piece of data is modified by the CPU, it must be stored or written back out to main memory so that the rest of the system has access to the most up-to-date version ...