System variable symbols are a special class of variable symbols, starting with the characters &SYS. Their values are set by the assembler according to specific rules. You cannot declare them in local-scope SET symbols or global-scope SET symbols, nor use them as symbolic parameters in macro prototype statements. You can use these symbols as points of substitution in model statements and conditional assembly instructions.

All system variable symbols are subject to the same rules of concatenation and substitution as other variable symbols.

A description of each system variable symbols begins with &SYSADATA_DSN System Variable Symbol.

Do not prefix your SET symbols with the character sequence &SYS. The assembler uses this sequence as a prefix to all system variable symbol names, and using them for other SET symbol names might cause future conflicts.