Summary of source and object program structures

The differences between the load module model and the program object model, and their interactions with assembler language instructions, are summarized in the following table:

Table 1. Object program structure comparison
Property	"Load Module" Model	"Program Object" Model
Form of object program	One-dimensional module	Two-dimensional module
Smallest indivisible independently relocatable component	Control section	Element and part
Residence Mode	Only one	One per class
Addressing Mode	Only one	One per entry point
Compatibility	Can be converted to program object	Can be converted to load module with limitations
Assembler Option	NOGOFF or GOFF	GOFF only
Assembler statements	CSECT, RSECT, START	CSECT, RSECT, START, CATTR, XATTR
Assignable loadable-program attributes	RMODE	RMODE, alignment, load type
External symbol types	SD/CM, LD, ER/WX, PR	SD, ED, LD, ER/WX, PR, PD
External symbol maximum length	8 characters	256 characters
External symbol scope	Module (WX), Library (ER)	Section, Module, Library, Import/Export
External symbol attributes	AMode, RMode	AMode, RMode, scope, PSect name, linkage type, reference type, extended attributes
Object module record types	ESD, TXT, RLD, END, SYM	HDR, ESD, TXT, RLD, END, LEN
Address constant types	A, V, Q, CXD	A, V, Q, J, R, CXD
Binding attributes	Catenate (SD),Merge-like (CM,PR)	Catenate (non-Merge classes), Merge classes (Parts, Pseudo-Registers)
Text types	Byte stream	Byte stream, records (structured and unstructured)
Maximum contiguous text length	16 MB	1 GB