Problem programs which execute in CMS can create files on unlabeled
tape in any record and block size; the record format can be fixed,
variable, or undefined. Figure 1 describes the CMS file system.
Program Development
The Conversational Monitor System includes commands to create and compile source programs, to modify and correct source programs, to build
test files, to execute test programs and to debug from the terminal.
The commands of CMS are especially useful for as and DOS/VS program
development, but also may be used in combination with other operating systems to provide a virtual machine program development tool. CMS utilizes the as and DOS/VS compilers via interface modules; the compilers themselves normally are not changede In order to provide
suitable interfaces, CMS includes a certain degree of as and DOS/VS simulation. The sequential, direct, and partitioned access methods are
logically simulated; the data are physically kept in the chained SOO-byte blocks that are standard to CMS, and are processed internally
to simulate as data set characteristics. CMS supports VSAM catalogs,
data spaces, and files on as and DOS disks using the DOS/VS Access Method Services. as Supervisor Call functions such as GETMAIN/FREEMAIN and TIME are simulated. The simulation restrictions concerning what
types of as object programs can be executed under CMS are primarily
related to the as/pcP, MFT, and MVT Indexed sequential Access Method (ISAM) and the telecommunications access methods, while functions
related to multitasking in as and DOS/VS are ignored by CMS. For more
information, see "as Macro simulation under CMS" and "DOS/VS Support under CMS." CMS Introduction 2-5

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