Two sets of commercial PL/I programs are studied. One set represents programming practice before the introduction of structured programming techniques and the other set after their introduction. The use of these new methods is found to make a measurable difference on the quality of the programs. A few minor changes in the use of PL/I are noted. Substantial modifications to the control structure of the programs are measured. Also, some improvements in the qualitative aspects of the two sets are discussed. Although, they are much improved, further alterations can make the programs still better. The time and training required to introduce structured programming techniques will begin paying dividends within six months.

Abstract A sample of 120 production PL/I programs from several commercial computing installations has been studied. Data about the programs in the sample have been extracted by a PL/I scanning program. The statistical results of the study are presented in this document The paper concentrates on statistical data and not on general conclusions. The data are only interpreted to the extent that it is not ill‐defined and misleading. The data profile the use of basic PL/I elements and the structure of programs written in PL/I. The reader of this report will get a better understanding of how PL/I has been used in the commercial environment up to 1974.

The source code for 120 production PL/I programs from several General Motors' commercial computing installations has been collected. The programs have been scanned both manually and automatically. Some data from the scanning process are presented and interpreted.

Abstract A method of handling asynchronous interrupts, which are defined to be events, in a highlevel, block‐structured language is described. The language facilities are based on PL/1 conditions. The functions of an interrupt handler and its relationship with the execution time support for the language are defined and discussed. The development of the facilities being presented is also described. Solutions to design problems and implemenation details are stated. The use and benefits of the mechanism are discussed.