HP 3000 Manuals

HP System Dictionary XL Gen. Ref. Vol. 1

Internal Numbering 

System Dictionary associates an internal number to each component within
System Dictionary.  The responsibility for these numbers is completely
under the control of System Dictionary.  The number value System
Dictionary assigns to a particular component does not necessarily follow
any set pattern.  The SDMAIN program and the System Dictionary intrinsics
use internal numbering.

MPE/iX 5.0 Documentation