Mainframe is a big computing machine which handles much number of users throughout the world. Any number of users can connect to one mainframe machine from different areas of the world. Applications are written in Cobol, Assembler, JCL, CICS, FORTRAN, C, Java runs on this machine. Databases like IBM DB2, IMS DB...are used on this machine. A mainframe system is introduced into market by the company IBM.
COBOL: COBOL is nothing but Common Business Oriented Language .It is a high-level Programming language. All the instructions belonging to Mainframe are written in COBOL language.
JCL: JCL means Job Control Language. It is the command language of Multiple Virtual Storage Operating System. JCL identifies the program which is going to be executed, the inputs and location of the input/output and informs them to the Operating System by Job control Statements. All Programs are executed in batch and online modes only. JCL is used for submitting a program for execution in batch mode. A job is a set of work which can be done by many job steps. Every step is specified in JCL through a set of Job Control Statements.
DB2: It is a database from IBM. It is a Relational Database Management System,designed to store, access and retrieve the data. It is designed for middle size to large size business organizations. It is designed for Workgroup or mid-size business organizations. It allows only single application developer. It is useful to design and build the applications for deployment.
VSAM: VSAM refers Virtual Storage Access Method. It is a high efficient access method used to organize the data in form of files or records in Mainframes system. It is used by COBOL and CICS in Mainframes to store, retrieve and access the data. It makes it easier for applications to execute an input-output operations. It is a file system used in MVS, OS/390 and ZOS operating systems. It provides standard sequential files, key-sequential,indexed files. In this Files can be read sequentially as well as randomly.
CICS: It refers to Customer Information Control System is introduced by IBM.
It is used to support online programming on Mainframes. CICS acts like a sub-os, it manages memory space, control the execution of applications. CICS is itself is a batch job running on Mainframe to offer application programs to respond to online requests any time.