title: JCL exclusive access to data set error
body: <p>According to MVS JCL Reference guide before the job start it requests the exclusive control of a data set:</p>
  
  <pre><code>DISP and ENQ: Before starting the first step of a job, the initiator requests
  control of all of the data sets in that job by issuing an ENQ for each of them,
  using the value specified for DISP to determine the kind of ENQ issued. The
  initiator issues the ENQ for each data set at the highest level required for that
  data set by any step of the job. For example, if all steps of the job request
  shared control of a specific data set (DISP=SHR) then the ENQ for that data set
  is requested as SHR. If, on the other hand, any step of the job requests
  exclusive control of a specific data set (DISP=NEW, DISP=MOD, or DISP=OLD), then
  the ENQ for that data set is requested EXCL.
  </code></pre>
  
  <p>But I got two different behaviors:</p>
  
  <p>a) I open through ISPF DATASET_A and submit a JCL that uses the same data set with DISP=(NEW,CATALOG,DELETE). I get a TSO message because the data set is requested by the job and the JCL won't start until I release the data set through ISPF.</p>
  
  <p>b) I submit 2 JCL's that use the same data set with DISP=(NEW,CATALOG,DELETE) but both start at the same time.</p>
  
  <p>Why don't the jobs request exclusive access to the data set when running in parallel?</p>