Address constant
assembly language data type
In IBM System/360 through present day z/Architecture, an address constant or "adcon" is an assembly language data type which contains the address of a location in computer memory. An address constant can be one, two, three or four bytes long, although an adcon of less than four bytes is conventionally used to hold an expression for a small integer such as a length, a relative address, or an index value, and does not represent an address at all. Address constants are defined using an assembler language "DC" statement.
Other computer systems have similar facilities, although different names may be used.
Types of address constants
A adcons normally store a four byte relocatable address, however it is possible to specify the length of the constant. For example, AL1(stuff) defines a one-byte adcon, useful mainly for small constants with relocatable values. Other adcon types can similarly have length specification.
V type adcons store an external reference to be resolved by the link-editor.
Y is used for two byte (halfword) addresses. 'Y' adcons can directly address up to 32K bytes of storage, and are not widely used since early System/360 assemblers did not support a 'Y' data type.
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