Assembler
The low-level programming language of the mainframe, where each statement matches a single machine instruction.
Also written HLASM, High Level Assembler, assembly language, BAL
Assembler is the programming language closest to the machine. Each instruction in an assembler program matches one instruction the processor runs, such as loading a value into a register or adding two numbers. IBM's assembler for z/OS is called High Level Assembler, or HLASM.
It is used where full control or speed matters. Parts of z/OS and its subsystems are written in assembler, and so are many exits: small pieces of site code that z/OS, JES or CICS call at set points to change how they behave. Some older applications use it for routines that need to be very fast.
Assembler also uses macros, ready-made pieces of code for common tasks, such as opening a file or writing a message to the console. Much of the work of writing assembler is knowing which macros to use.
Most new application work is in COBOL, Java or other languages, and many developers never write assembler. Being able to read a little helps, though, because dumps and compile listings show machine instructions, and older systems often contain a few assembler routines that someone has to look after.
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- COBOLThe programming language most business logic on the mainframe is written in. Verbose by design, and still running the world's payments.
- CompileTurning COBOL source code into machine instructions, checking the syntax and producing a listing of any errors.
- Load moduleThe runnable form of a program, stored in a library, which JCL executes by name.
- DumpA copy of a program's memory taken at the moment it failed, used to find out why.
- System programmerThe person who installs, configures, tunes and upgrades the operating system and its subsystems.