ABCs of z/OS System Programming Volume 3 - IBM Redbooks

2.1 Data sets on storage devices
DASD volume
DATASET.SEQ
DATASET.PDS
DATASET.VSAM
VOLSER=DASD01
Figure 2-1 Data sets on volumes
Tape volume
DATASET.SEQ1
DATASET.SEQ2
DATASET.SEQ3
VOLSER=SL0001
MVS data sets
An MVS data set is a collection of logically related data records stored on one volume or a set
of volumes. A data set can be, for example, a source program, a library of macros, or a file of
data records used by a processing program. You can print a data set or display it on a
terminal. The logical record is the basic unit of information used by a processing program.
Note: As an exception, the z/OS UNIX services component supports Hierarchical File
System (HFS) data sets, where the collection is of bytes and there is not the concept of
logically related data records.
Storage devices
Data can be stored on a magnetic direct access storage device (DASD), magnetic tape
volume, or optical media. As mentioned previously, the term DASD applies to disks or
simulated equivalents of disks. All types of data sets can be stored on DASD, but only
sequential data sets can be stored on magnetic tape. The types of data sets are described in
2.3, “DFSMSdfp data set types” on page 20.
DASD volumes
Each block of data on a DASD volume has a distinct location and a unique address, making it
possible to find any record without extensive searching. You can store and retrieve records
either directly or sequentially. Use DASD volumes for storing data and executable programs,
Chapter 2. Data set basics 17