High Level Assembler (HLASM) is IBM's assembler programming language and the assembler itself for the IBM z/OS, z/VM, OS/390, MVS, VM, and VSE operating systems. Released in June 1992, HLASM was the first new assembler language from IBM in twenty years. Version 4 was released in September 2000.
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In common with other assembler (sometimes known as assembly) programs, HLASM translates basic computer instructions (such as Load, for example, which instructs the processor to move data from memory to a register) to machine code, the binary information that is all that computers understand.
HLASM replaced IBM's earlier assembler programs, Assembler H Version 2, Assembler XF, DOS/VSE, and VSE/AF. IBM claims that HLASM features a number of improvements over other assembler programs. HLASM includes support for existing applications through such measures as extensions to earlier IBM assemblers. Automation of common tasks and cross-reference features was included to make programming and administrative tasks easier and less time-consuming, while improved diagnostics were developed to find common, but hard-to-find coding errors more quickly. The HLASM Toolkit, an optional feature, includes additional development, diagnosis, and recovery tools.