In the 1990s, the format was given an extension with the XSD-type record for the MVS Operating System to support longer module names in the C Programming Language.
But, it was a good choice as it was satisfactory for the needs of programming languages being used at the time, it did work and was simple to implement (especially where machines at the time may have had as little as 8K of memory, many operating multiple concurrent or consecutive jobs with as little as 64K, and actually performing useful work), simple to use and for simple programs (object orientation and concepts like virtual methods would be decades in the future from when it was originally developed), can still be adequate.
This format has the advantage that it is easy and simple to create, and a compiler for a language that can live with its restrictions, which are maximum 8-character upper-case only module names, applications no larger than 2^24 in size (16 megabytes) for code and data, means that any programming language that can write 80-byte fixed-format binary files (basically anything including COBOL and FORTRAN, not just Assembler), can be used to create a compiler for this object format.
The assembler, (or compiler, in the case of a high-level language such as C, COBOL, Fortran, Pascal, PL/I or RPG III), would create an ESD record for each subroutine, function, or program, and for Common Blocks in the case of Fortran programs.
Optionally, a language can provide symbolic reference information such as object names and data type information or debugging symbols through SYM records, and then the END statement indicates the end of an Object module file and the optional start address for the subroutine, function or program that this file should be started at, if the starting address for the routine is not the first byte of the first routine (some routines may have non-executable data preceding their actual code or the first routine assembled or compiled is not the "main" program or "primary" module.)
The COBOL compiler typically discards the dash character if it appears in a program's PROGRAM-ID or a CALL statement to an external module.
In the 1990s, a new record type, the XSD record was added to extend the use of this object module format to encompass longer module names than 8 characters and to permit mixed-case names, as required by the C programming language.
To make this simple, presume for example a C program named basura calls the exit() function.