If you want to take advantage of automatic boundary alignment (if the ALIGN option is specified) and implicit length calculation, do not supply a length modifier in your operand specifications. Instead, specify a type subfield that corresponds to the type of area you need for your instructions.

Using a length modifier can give you the advantage of explicitly specifying the length attribute value assigned to the label naming the area reserved. However, your areas are not aligned automatically according to their type. If you omit the nominal value in the operand, use a length modifier for the binary (B), character (C), graphic (G), hexadecimal (X), and decimal (P and Z) type areas. If you do not, their labels are given a length attribute value of 1 (2 for G and CU type).

When you need to reserve large areas, you can use a duplication factor. However, in this case, you can only refer to the first area by its label. You can also use the character (C) and hexadecimal (X) field types to specify large areas using the length modifier. Duplication has no effect on implicit length.

Although the nominal value is optional for a DS instruction, you can put it to good use by letting the assembler compute the length for areas of the B, C, G, X, and decimal (P or Z) type areas. You achieve this by specifying the general format of the nominal value that is placed in the area at execution time.

If a nominal value and no length modifier are specified for a Unicode character string, the length of the storage reserved is derived by multiplying by two the number of characters specified in the nominal value (after pairing).