HLASM Language Reference

Introduction
Chapter 1. Introduction
A computer can understand and interpret only machine language. Machine
language is in binary form and, thus, very difficult to write. The assembler
language is a symbolic programming language that you can use to code
instructions instead of coding in machine language.
Because the assembler language lets you use meaningful symbols made up of
alphabetic and numeric characters, instead of just the binary digits 0 and 1 used in
machine language, you can make your coding easier to read, understand, and
change. The assembler must translate the symbolic assembler language into
machine language before the computer can run your program. The specific
procedures followed to do this may vary according to the system you are using.
However, the method is basically the same for all systems:
┌───────────────────┐
│ Your assembler │
│ language source ├─────┐
│ statements │ │
└───────────────────┘ │
▼
┌───────────┴───────────┐
│ HIGH LEVEL ASSEMBLER │
└─────────┬───┬─────────┘
│ │
│ │
┌──────────┐ │ │ ┌──────────────────┐
│ Messages │ │ │ │ Machine language │
│ and ├◄───────────┘ └──────────►┤ version of your │
│ listings │ │ program │
│ . │ └─────────┬────────┘
│ . │ │
└────┬─────┘
│
▲
│
│
│
│ ┌─────────────────┐ │
│ │ LINKER ├◄─────────────┘
│
└──────┬───┬──────┘
│ │ │
│ │ │ ┌───────────────────┐
└──────────────────┘ └──────────►┤ Executable module │
└───────────────────┘
Figure 2. Assembling and Link-Editing Your Assembler Language Program
Your program, written in the assembler language, becomes the source module that
is input to the assembler. The assembler processes your source module and
produces an object module in machine language (called object code). The object
module can be used as input to be processed by the linker or the binder. The
linker or binder produces a load module (MVS and CMS), or a phase (VSE), that
can be loaded later into the main storage of the computer. When your program is
loaded, it can then be run. Your source module and the object code produced are
printed, along with other information, on a program listing.
© Copyright IBM Corp. 1982, 2004 3