Reference pattern services allow HLL programs to define a reference pattern for a specified area of virtual storage that the program is about to reference. Additionally, the program specifies how much data it wants the operating system to bring into central storage at one time. Data and instructions in virtual storage must reside in central storage before they can be processed. The system honors the request according to the availability of central storage. By bringing in more data at one time, the system might improve the performance of your program.

The term reference pattern refers to the order in which a program’s instructions process a range of data, such as an array or part of an array.

Programs that benefit most from reference pattern services are those that reference amounts of data that are greater than one megabyte. The program should reference the data in a sequential manner and in a consistent direction, either forward or backward. In forward direction, the program references data elements in order of ascending addresses. In backward direction, the program references data elements in order of decreasing addresses. In addition, if the program "skips over" certain areas, and these areas are of uniform size and are repeated at regular intervals throughout the area, reference pattern services might provide additional performance improvement.

A program might have a number of different ways of referencing a particular area. In this case, the program can issue multiple pairs of CSRIRP and CSRRRP services for the area. Only one pattern can be in effect at a time.

Although reference pattern services can be used for data structures other than arrays, for simplicity, examples in Introduction to reference pattern services and Using reference pattern services use the services with arrays.