A method for cooling a data center having a plurality of racks and an adjustable cooling system includes the following steps. One electrode of the capacitor element is connected to one storage node of a flip-flop circuit, and the other electrode is connected to the other storage node. The first head is configured for placement on a first side of the substrate. At least the content may be provided to the signage controller, which may cause the digital signage to display some of the content. The block count for each active stripe can be the number of data blocks belonging to the same stripe that are stored in the cache memory.