Within a z/OS environment, data resides across a storage hierarchy. Each level of this hierarchy is represented in hardware by a different component, and the amount of each component in a system is usually variable between some minimum and maximum levels. A typical representation of these components (from top to bottom) would be:

1. Processor cache
2. Central storage
3. Storage control cache
4. Disk
5. Tape

The components at the top of the hierarchy (processor cache, central storage) are somewhat expensive on a per-byte basis (and thus relatively small in capacity), but have very fast access times. In contrast, the components at the bottom of the hierarchy (disk, tape) are relatively inexpensive and have very large capacities, but their access rates are considerably slower. As you go from top to bottom in the hierarchy, the components typically get less expensive per byte, have higher capacities, and have slower access times.

DFSORT attempts to take advantage of all the levels of the storage hierarchy. The following sections briefly describe how DFSORT accomplishes this.