Caching modes

There are three basic caching modes: read cache, write cache and read/write cache. In the diagrams below, read accesses are represented by arrows on the left and write accesses by arrows on the right.

In the following section, a cache operated in the mode “read caching”, “write caching” or “read/write caching” is also referred to as read cache, write cache or read/write cache.

The DAB functions are executed under the user task. A separate system task is only created for asynchronous saving to disk.

Read caching

Figure 2: I/O sequence with read caching

Write caching

Figure 3: I/O sequence with write caching

Read/write caching

Figure 4: I/O sequence with read/write caching