PL/I uses two types of data transmission: stream and record.

• In stream-oriented data transmission, the organization of the data in the data set is ignored within the program, and the data is treated as though it were a continuous stream of individual data values in character form. Data is converted from character form to internal form on input, and from internal form to character form on output.
• In record-oriented data transmission, the data set is a collection of discrete records. The record on the external medium is generally an exact copy of the record as it exists in internal storage. No data conversion takes place during record-oriented data transmission. On input, the data is transmitted exactly as it is recorded in the data set, and on output, it is transmitted exactly as it is recorded internally.

Stream-oriented data transmission is more versatile than record-oriented data transmission in its data-formatting abilities, but is less efficient in terms of run time.

Record-oriented data transmission is more versatile than stream-oriented data transmission, in both the manner in which data can be processed and the types of data sets that it can process. Since data is recorded in a data set exactly as it appears in main storage, any data type is acceptable. No conversions occur, but you must have a greater awareness of the data structure.