High Quality Content by WIKIPEDIA articles! In an IBM mainframe, the job stream is the path of execution that a job takes. The JCL and any data submitted with it form the job stream. There can be multiple EXEC and DD statements in a job stream if a job involves more than one program. IBM mainframes, are large computer systems produced by IBM from 1952 to the present. During the 1960's and 1970's, the term mainframe computer was almost synonymous with IBM products due to their marketshare. Current mainframes in IBM's line of business computers are developments of the basic design of the IBM System/360.