Each C/I text record represents one JCL statement. This record, or text string, is built in an 8192-byte buffer. The length of the used data area of this buffer is specified by a 2-byte field at the beginning of the text string. If modifications are made, it is the user's responsibility to ensure that the data in this length field is correct.

The C/I text string for a record contains a hexadecimal value to indicate the statement type, such as JOB statement, EXEC statement, or last DD statement, among others. The text string also contains a specific key value (called the verb key) to identify the type of JCL statement (such as JOB, EXEC, DD).

The information for one type of JCL statement differs from the information for another, depending on the presence of parameters and subparameters. In general, however, the text strings adhere to a common format. Each C/I text record contains prefix information and an end-of-text indicator. In addition, key entries are defined for parameters in the text string. Positional information specified may be represented in the prefix and/or in the key entries.