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126 IBM VM/370 eMS User's Guide

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Section 8. Developing OS Programs under eMS eMS simulates many of the functions of the Operating System (OS), allowing you to compile, execute and debug as programs interactively.
For the most part, you do not need to be concerned with the eMS OS simulation routines; they are built into the CMS system. Before you can
compile and execute as programs in CMS, however, you must be acquainted
with the following: • OS macros that eMS can simulate • Using as data sets in CMS • How to use the FILEDEF command • creating CMS files from OS data sets • using CMS and OS macro libraries • Assembling programs in CMS • Executing programs These topics are discussed below. Additional information for as VSAM users is in "Section 10. Using Access Method Services and VSAM Under CMS and CMS/DOS." For a practice terminal session using the commands and techniques
presented in section 8, see "Appendix D: Sample Terminal Sessions.r. The eMS system uses many OS terms, but there are a number of OS functions that CMS performs somewhat differently. To help you become
familiar with the some of the CMS equivalents (where they do exist) for OS terms and functions, see Figure 11. It lists some commonly-used OS terms and discusses how CMS handles the functions they imply. Section 8. Developing as Programs Under CMS 127