The other option is to only write to cache, and write to the backing store later. This is known as write-back (or write-behind) cache. The cache marks the entries that have not yet been written to the backing store; the mark that is used is often referred to as dirty flag. Before the entries are deleted from the cache, they are written to the backing store. This is known as lazy write. A miss in a write-back cache (which requires a block to be replaced by another) will often need two memory accesses: one to get the needed datum, and another to write replaced data from the cache to the store.