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.
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.