CICS Service Diagram
Terminal
Control
(VTAM,SNA,TCP/IP)
Basic
Mapping
Support
Terminal User
Application
Programming
Interface
Application
Program
Maps
File Control
SQL
DL/I
VSAM
DB2
IMS
OS/390
CICS
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•The most popular operating system to run CICS is OS/390.
•The Red boxes show the services under control of CICS.  These include the program API, Basic Mapping Services (BMS), and Terminal Control
•The White boxes show the services under control of the operating system, in this case OS/390.  These services include communication protocols, such as  TCP/IP, the databases and file systems that store data, such as DB2, and the actual application program that will accomplish the task.
•The Blue box represents the outside user of the system.  This is the end user of the CICS application.[Menendez]