Measure the size in

You can specify the size in megabytes (MB) or cylinders. The primary amount is the initial amount allocated to the data set; the secondary amount is what can be added if it needs more space. The data set is always allocated in cylinders; the megabytes are converted to cylinders.

For example, a data set created with 5 primary cylinders and 1 secondary cylinder causes 5 cylinders to be allocated to the data set; if it needs more space, it can obtain 1 additional cylinder.

The wizard uses a primary amount of 50 and a secondary amount of 1 as the default.