Under z/OS: use the SYSTRACE DD statement to define the Internal Trace Facility output data set:

//SYSTRACE DD DSN=dsname,DISP=(NEW,CATLG),SPACE=(CYL,(primary,secondary)),
//          DCB=(LRECL=81,BLKSIZE=n*81,RECFM=F)

Under CMS: issue the SYSTRACE FILEDEF command before the High Level Assembler command, to specify the output trace data set. For example, you could specify:

FILEDEF SYSTRACE DISK fn SYSTRACE m1 (RECFM F LRECL 81

If you do not do this, High Level Assembler will issue this FILEDEF command for you.

Under z/VSE: use the following JCL to specify the output trace data set:

// ASSGN SYSTRAC,DISK,VOL=volser,SHR
// DLBL SYSTRAC,'dsname',0,SD
// EXTENT SYSTRAC,volser,1,0,start,tracks